Meiosis in horses refers to the specialized type of cell division that reduces the chromosome number by half, resulting in the formation of gametes—sperm in males and eggs in females. This process is fundamental for sexual reproduction, ensuring genetic diversity and stability across generations. During meiosis, homologous chromosomes undergo pairing, recombination, and segregation, leading to genetically unique gametes. Research on equine meiosis explores the mechanisms and stages of this process, the genetic factors involved, and its implications for fertility and breeding. This page compiles peer-reviewed research studies and scholarly articles that investigate the cellular and molecular aspects of meiosis in horses, as well as its impact on equine reproductive health.
Song X, Jiang H, Lv P, Cui K, Liu Q, Yin S, Liu H, Li Z.Oocyte in vitro maturation is necessary for the study and application of animal-assisted reproduction technology in animal reproduction and breeding. The comprehensive transcriptional profile of equine oocyte maturated in vitro has not been fully mined yet, which makes many key transcriptional events still unidentified. Here, Smart-seq2 was performed to analyse the gene expression pattern and the underlying regulatory mechanism of horse germinal vesicle (GV) and in vitro metaphase II (MII) oocytes. The results showed that 6402 genes (2640 up-regulated and 3762 down-regulated in MII samples com...
Leal GR, Monteiro CAS, Carvalheira LR, Souza-Fabjan JMG.Simulated Physiological Oocyte Maturation (SPOM) mimics in vitro the physiological events of oocyte maturation. The system uses cAMP modulators in two steps (pre IVM and IVM) and has presented promising results that are arousing the curiosity of IVF programs in different animal species, generating several papers, adaptations, and controversies worldwide. This study systematically analyses the data in the literature on the use of SPOM and compares the outcomes to the original paper (Albuz et al. Hum. Rep., 25: 2999-3011 2010), classifying them into success or failure. The PubMed, Scopus, and ...
Castaneda C, Ruiz AJ, Tibary A, Raudsepp T.We present a detailed molecular cytogenetic analysis of a reciprocal translocation between horse (ECA) chromosomes Y and 13 in a Friesian stallion with complete meiotic arrest and azoospermia. We use dual-color fluorescence in situ hybridization with select ECAY and ECA13 markers and show that the translocation breakpoint in ECAY is in the multicopy region and in ECA13, at the centromere. One resulting derivative chromosome, Y;13p, comprises of ECAY heterochromatin (ETSTY7 array), a small single copy and partial Y multicopy region, and ECA13p. Another derivative chromosome 13q;Y comprises of E...
Scarlet D, Handschuh S, Reichart U, Podico G, Ellerbrock RE, Demyda-Peyrás S, Canisso IF, Walter I, Aurich C.It was the aim of this study to characterize the development of the gonads and genital ducts in the equine fetus around the time of sexual differentiation. This included the identification and localization of the primordial germ cell population. Equine fetuses between 45 and 60 days of gestation were evaluated using a combination of micro-computed tomography scanning, immunohistochemistry, and multiplex immunofluorescence. Fetal gonads increased in size 23-fold from 45 to 60 days of gestation, and an even greater increase was observed in the metanephros volume. Signs of mesonephros atrophy wer...
Rizzo M, du Preez N, Ducheyne KD, Deelen C, Beitsma MM, Stout TAE, de Ruijter-Villani M.Aneuploidy of meiotic origin is a major contributor to age-related subfertility and an increased risk of miscarriage in women. Although age-related aneuploidy has been studied in rodents, the mare may be a more appropriate animal model to study reproductive aging. Similar to women, aged mares show reduced fertility and an increased incidence of early pregnancy loss; however, it is not known whether aging predisposes to aneuploidy in equine oocytes. We evaluated the effect of advanced mare age on (1) gene expression for cohesin components, (2) incidence of aneuploidy and (3) chromosome centrome...
Li B, He X, Zhao Y, Bai D, Du M, Song L, Liu Z, Yin Z, Manglai D.Horse testis development and spermatogenesis are complex physiological processes. To study these processes, three immature and three mature testes were collected from the Mongolian horse, and six libraries were established using high-throughput RNA sequencing technology (RNA-Seq) to screen for genes related to testis development and spermatogenesis. A total of 16,237 upregulated genes and 8,641 downregulated genes were detected in the testis of the Mongolian horse. These genes play important roles in different developmental stages of spermatogenesis and testicular development. Five genes with ...
Centromeres exert an inhibitory effect on meiotic recombination, but the possible contribution of satellite DNA to this "centromere effect" is under debate. In the horse, satellite DNA is present at all centromeres with the exception of the one from chromosome 11. This organization of centromeres allowed us to investigate the role of satellite DNA on recombination suppression in horse spermatocytes at the stage of pachytene. To this aim we analysed the distribution of the MLH1 protein, marker of recombination foci, relative to CENP-A, marker of centromeric function. We demonstrated that the sa...
Lodde V, Colleoni S, Tessaro I, Corbani D, Lazzari G, Luciano AM, Galli C, Franciosi F.Several studies report that a two-step culture where mammalian oocytes are first kept under meiosis-arresting conditions (prematuration) followed by IVM is beneficial to embryo development. The most promising results were obtained by stratifying the oocyte population using morphological criteria and allocating them to different culture conditions to best meet their metabolic needs. In this study, horse oocytes were characterised to identify subpopulations that may benefit from prematuration. We investigated gap-junction (GJ) coupling, large-scale chromatin configuration and meiotic competence ...
Pereira B, Dorado J, Diaz-Jimenez M, Consuegra C, Ortiz I, Gosalvez J, Hidalgo M.The acquisition of equine oocyte developmental capacity is ensured by the follicular environment, such as granulosa cells, which could reflect the meiotic development potential of immature oocytes. This study evaluated the relationship between DNA fragmentation of granulosa cells, using the chromatin dispersion test, and equine oocyte meiotic development after in vitro maturation. Granulosa cells and cumulus-oocytes complexes (n = 50) were recovered from slaughterhouse-derived ovaries. Oocytes were in vitro matured, stained and evaluated under fluorescence microscopy. Maturation rates were c...
Beeson SK, Mickelson JR, McCue ME.Total genetic map length and local recombination landscapes typically vary within and across populations. As a first step to understanding the recombination landscape in the domestic horse, we calculated population recombination rates and identified likely recombination hotspots using approximately 1.8 million SNP genotypes for 485 horses from 32 distinct breeds. The resulting breed-averaged recombination map spans 2.36 Gb and accounts for 2939.07 cM. Recombination hotspots occur once per 23.8 Mb on average and account for ∼9% of the physical map length. Regions with elevated recombination r...
Ducheyne KD, Rizzo M, Daels PF, Stout TAE, de Ruijter-Villani M.Vitrified-warmed immature equine oocytes are able to complete the first meiotic division, but their subsequent developmental competence is compromised. Therefore, the present study investigated the effects of vitrifying immature horse oocytes on the chromosome and spindle configuration after IVM. Cumulus-oocytes complexes (COCs) were collected and divided into two groups based on mare age (young ≤14 years; old ≥16 years). COCs were then either directly matured invitro or vitrified and warmed before IVM. Spindle morphology and chromosome alignment within MII stage oocytes were assessed usin...
Rizzo M, Ducheyne KD, Deelen C, Beitsma M, Cristarella S, Quartuccio M, Stout TAE, de Ruijter-Villani M.Advanced mare age is associated with declining fertility and an increased risk of early pregnancy loss. Compromised oocyte quality is probably the primary reason for reduced fertility, but the defects predisposing to embryonic death are unknown. In women, advanced age predisposes to chromosome segregation errors during meiosis, which lead to embryonic aneuploidy and a heightened risk of miscarriage. Objective: To evaluate the effect of advanced mare age on chromosome alignment and meiotic spindle morphology in in vitro-matured (IVM) oocytes. Methods: Morphometric and morphological analysis. M...
Ketchum CC, Larsen CD, McNeil A, Meyer-Ficca ML, Meyer RG.Chromatin remodeling during spermatogenesis culminates in the exchange of nucleosomes for transition proteins and protamines as an important part of spermatid development to give rise to healthy sperm. Comparative immunofluorescence analyses of equine and murine testis histological sections were used to characterize nucleoprotein exchange in the stallion. Histone H4 hyperacetylation is considered a key event of histone removal during the nucleoprotein transition to a protamine-based sperm chromatin structure. In the stallion, but not the mouse, H4 was already highly acetylated in lysine residu...
González-Fernández L, Sánchez-Calabuig MJ, Alves MG, Oliveira PF, Macedo S, Gutiérrez-Adán A, Rocha A, Macías-García B.Equine cumulus-oocyte complexes (COCs) are classified as compact (cCOC) or expanded (eCOC) and vary in their meiotic competence. This difference could be related to divergent glucose metabolism. To test this hypothesis in the present study, eCOCs, cCOCs and expanded or compact mural granulosa cells (EC and CC respectively) were matured in vitro for 30h, at which time maturation rate, glucose metabolism and the expression of genes involved in glucose transport, glycolysis, apoptosis and meiotic competence were determined. There were significant differences between eCOCs and cCOCs in maturation ...
Franciosi F, Tessaro I, Dalbies-Tran R, Douet C, Reigner F, Deleuze S, Papillier P, Miclea I, Lodde V, Luciano AM, Goudet G.The field of assisted reproduction has been developed to treat infertility in women, companion animals, and endangered species. In the horse, assisted reproduction also allows for the production of embryos from high performers without interrupting their sports career and contributes to an increase in the number of foals from mares of high genetic value. The present manuscript describes the procedures used for collecting immature and mature oocytes from horse ovaries using ovum pick-up (OPU). These oocytes were then used to investigate the incidence of aneuploidy by adapting a protocol previous...
Bertero A, Ritrovato F, Evangelista F, Stabile V, Fortina R, Ricci A, Revelli A, Vincenti L, Nervo T.The purpose of this study was to observe -matured equine oocytes with an objective computerized technique that involves the use of a polarized light microscope (PLM) in addition to the subjective morphological evaluation obtained using a classic light microscope (LM). Equine cumulus-oocyte complexes (COCs, = 922) were subjected to different maturation times (24, 36 or 45 h), however, only 36-h matured oocytes were analyzed using CLM. The 36-h matured oocytes that reached maturity were parthenogenetically activated to evaluate the quality and meiotic competence. Average maturation perce...
Canesin HS, Brom-de-Luna JG, Choi YH, Ortiz I, Diaw M, Hinrichs K.We evaluated the meiotic and developmental competence of GV-stage equine oocytes vitrified under different conditions. In a preliminary study, using dimethyl sulfoxide (D), ethylene glycol (EG) and sucrose (S) as cryoprotectants, the maturation rate was higher for cumulus-oocyte complexes (COCs) held overnight before vitrification (37%) than for those vitrified immediately (14%; P < 0.05). Thereafter, all COCs were held overnight before vitrification. In Experiment 1 we compared 1 min (1m) and 4 min (4m) exposure to vitrification and warming solutions; oocytes that subsequently matured wer...
Zeng W, Alpaugh W, Stefanovski D, Schlingmann K, Dobrinski I, Turner RM.The study of spermatogenesis in the horse is challenging because of the absence of an in vitro system that is capable of reproducing efficient spermatogenesis and because of the difficulties and costs associated with performing well-controlled studies in vivo. In an attempt to develop novel methods for the study of equine spermatogenesis, we tested whether cells from enzymatically digested pre-pubertal equine testicular tissue were capable of de novo tissue formation and spermatogenesis following xenografting under the back skin of immunocompromised mice. Testes were obtained from normal pre...
Raudsepp T, Chowdhary BP.The association between chromosomal abnormalities and reduced fertility in domestic animals is well recorded and has been studied for decades. Chromosome aberrations directly affect meiosis, gametogenesis, and the viability of zygotes and embryos. In some instances, balanced structural rearrangements can be transmitted, causing fertility problems in subsequent generations. Here, we aim to give a comprehensive overview of the current status and future prospects of clinical cytogenetics of animal reproduction by focusing on the advances in molecular cytogenetics during the genomics era. We descr...
Goudet G, Douet C, Kaabouba-Escurier A, Couty I, Moros-Nicolás C, Barrière P, Blard T, Reigner F, Deleuze S, Magistrini M.Most wild and domestic donkey breeds are currently endangered or threatened. Their preservation includes the creation of a Genome Resource Bank. Embryos cryopreservation allows the preservation of genetics from both male and female and is the fastest method to restore a breed. Because embryo production in vivo is limited in equids, our objective was to establish conditions for in vitro production of embryos in donkey using ovum pick up (OPU), IVM, IVF, and in vitro culture of zygotes. Donkey cumulus-oocyte complexes (COCs) were collected by transvaginal ultrasound-guided aspirations OPU in ...
Han H, Wang A, Liu L, Zhao G, Su J, Wang B, Li Y, Zhang J, Wu B, Sun W, Hu S, Li S, Zhao L, Li X.Most hinnies (female donkey×male horse) and mules (female horse×male donkey) are sterile with few reports of equine fertile hybrids. The main cause of this sterility is thought to be a meiotic block to spermatogenesis and oogenesis. This study compared the developmental features of the testes and a histological analyses of spermatogenesis in a male hinny with those of a normal, fertile stallion and Jack donkey. Hinny testes showed a thicker tunica albuginea, fewer blood vessels and more connective tissue in the testis parenchyma than those of the stallion and Jack donkey. Although the mean n...
González-Fernández L, Macedo S, Lopes JS, Rocha A, Macías-García B.Equine in vitro fertilization (IVF) is still inconsistent. In the present work, we studied how modified Whitten's (MW) medium and Tissue Culture Medium 199 (TCM) added with Foetal Bovine Serum (FBS; 10% v/v) or Bovine Serum Albumin (BSA; 7 mg/ml) affected equine gametes to subsequently run IVF trials. Compact (Cp) and expanded (Ex) cumuli equine oocytes were matured and placed in TCM or MW supplemented with BSA or FBS for 18-20 h (no sperm added). In Ex oocytes, TCM-199 added with FBS or BSA resulted in higher metaphase II (MII) rates (75.7% and 62.7%, respectively) than MW added with BSA (54%...
Huang J, Zhao Y, Bai D, Shiraigol W, Li B, Yang L, Wu J, Bao W, Ren X, Jin B, Zhao Q, Li A, Bao S, Bao W, Xing Z, An A, Gao Y, Wei R, Bao Y, Bao T....The donkey, like the horse, is a promising model for exploring karyotypic instability. We report the de novo whole-genome assemblies of the donkey and the Asiatic wild ass. Our results reflect the distinct characteristics of donkeys, including more effective energy metabolism and better immunity than horses. The donkey shows a steady demographic trajectory. We detected abundant satellite sequences in some inactive centromere regions but not in neocentromere regions, while ribosomal RNAs frequently emerged in neocentromere regions but not in the obsolete centromere regions. Expanded miRNA famil...
Martino NA, Dell'Aquila ME, Filioli Uranio M, Rutigliano L, Nicassio M, Lacalandra GM, Hinrichs K.Evaluation of mitochondrial function offers an alternative to evaluate embryo development for assessment of oocyte viability, but little information is available on the relationship between mitochondrial and chromatin status in equine oocytes. We evaluated these parameters in immature equine oocytes either fixed immediately (IMM) or held overnight in an Earle's/Hank's' M199-based medium in the absence of meiotic inhibitors (EH treatment), and in mature oocytes. We hypothesized that EH holding may affect mitochondrial function and that holding temperature may affect the efficiency of meiotic su...
Al-Jaru A, Goodwin W, Skidmore J, Raudsepp T, Khazanehdari K.Chromosome configurations and chiasma frequency during the metaphase I stage of spermatogenesis in the male horse are characterized in this work. The genome-wide frequency and distribution of chiasmata was detected as 49.45 ± 2.07 for 14 fertile stallions. All X and Y chromosomes shared a single chiasma at their pseudoautosomal region, while 1-4 chiasmata were observed in autosomal chromosomes. The chiasma frequency and distribution were further studied for 8 different bivalents identified by FISH in 5 fertile stallions. Genetic length was calculated from chiasmata data for the whole genome a...
Curcio Bda R, Pereira GR, Antunes LI, Boff AN, dos Santos FC, Lucas T, Nogueira CE, Corcini CD, Liu I, Deschamps JC.In vitro fertilization (IVF) procedures are limited by the inability to mature equine oocytes on in vitro methods. Objective: The aim of this study was to evaluate structural integrity of equine oocytes subjected to vitrification with a synthetic polymer (PVA). Methods: The effect of eGH and its relationship with IGF-I on in vitro maturation (IVM) were evaluated. Compact cumulus oocytes complexes (n=122) were cultured in TCM-199 with eGH, IGF-I or eGH+IGF-I for 30h at 38.5C in air with 5 % CO2. Oocytes were fixed after IVM or subjected to the vitrification protocol. Cryopreserved oocytes were ...
Jung HJ, Song H, Yoon MJ.Deleted in azoospermia-like (DAZL) is used as a germ cell marker in several species, including mice, rats, pigs, rhesus monkeys, bulls, and humans. Our objectives with this study were to investigate DAZL expression in stallion germ cells by using immunofluorescence, immunocytochemistry, and western blotting, and to determine the effects of reproductive stage and breeding season on the DAZL-positive cell population in seminiferous tubule cross sections. Testes were obtained during routine castration procedures at a large animal clinic and routine field service castration. The reproductive stage...
Al-Jaru A, Goodwin W, Skidmore J, Khazanehdari K.Advances in molecular cytogenetics have provided the opportunity to study events during prophase I of meiosis. Immunofluorescent localization of different meiotic protein components were used to characterize the early stages of the first meiotic division in horse spermatocytes. The frequency and distribution of recombination events during prophase I were investigated using the mutL homolog 1 (MLH1) protein that is known to be associated with these events. The frequency and distribution of MLH1 foci were investigated in pachytene nuclei of 6 fertile stallions, and the average relative synaptone...
Steiner CC, Ryder OA.Prdm9 (Meisetz) is the first speciation gene discovered in vertebrates conferring reproductive isolation. This locus encodes a meiosis-specific histone H3 methyltransferase that specifies meiotic recombination hotspots during gametogenesis. Allelic differences in Prdm9, characterized for a variable number of zinc finger (ZF) domains, have been associated with hybrid sterility in male house mice via spermatogenic failure at the pachytene stage. The mule, a classic example of hybrid sterility in mammals also exhibits a similar spermatogenesis breakdown, making Prdm9 an interesting candidate to e...
Fayrer-Hosken R, Stanley A, Hill N, Heusner G, Christian M, De La Fuente R, Baumann C, Jones L.The cellular effects of tall fescue grass-associated toxic ergot alkaloids on stallion sperm and colt testicular tissue were evaluated. This was a continuation of an initial experiment where the effects of toxic ergot alkaloids on the stallion spermiogram were investigated. The only spermiogram parameter in exposed stallions that was affected by the toxic ergot alkaloids was a decreased gel-free volume of the ejaculate. This study examined the effect of toxic ergot alkaloids on chilling and freezing of the stallion sperm cells. The effect of toxic ergot alkaloids on chilled extended sperm cell...
Ambruosi B, Uranio MF, Sardanelli AM, Pocar P, Martino NA, Paternoster MS, Amati F, Dell'Aquila ME.Phthalates are ubiquitous environmental contaminants because of their use in plastics and other common consumer products. Di-(2-ethylhexyl) phthalate (DEHP) is the most abundant phthalate and it impairs fertility by acting as an endocrine disruptor. The aim of the present study was to analyze the effects of in vitro acute exposure to DEHP on oocyte maturation, energy and oxidative status in the horse, a large animal model. Cumulus cell (CC) apoptosis and oxidative status were also investigated. Cumulus-oocyte complexes from the ovaries of slaughtered mares were cultured in vitro in presence of...
Rathi R, Honaramooz A, Zeng W, Turner R, Dobrinski I.Grafting of testis tissue from immature animals to immunodeficient mice results in complete spermatogenesis, albeit with varying efficiency in different species. The objectives of this study were to investigate if grafting of horse testis tissue would result in spermatogenesis, and to assess the effect of exogenous gonadotropins on xenograft development. Small fragments of testis tissue from 7 colts (2 week to 4 years of age) were grafted under the back skin of castrated male immunodeficient mice. For 2 donor animals, half of the mice were treated with gonadotropins. Xenografts were analyzed a...
Raudsepp T, Chowdhary BP.The association between chromosomal abnormalities and reduced fertility in domestic animals is well recorded and has been studied for decades. Chromosome aberrations directly affect meiosis, gametogenesis, and the viability of zygotes and embryos. In some instances, balanced structural rearrangements can be transmitted, causing fertility problems in subsequent generations. Here, we aim to give a comprehensive overview of the current status and future prospects of clinical cytogenetics of animal reproduction by focusing on the advances in molecular cytogenetics during the genomics era. We descr...
Arregui L, Rathi R, Zeng W, Honaramooz A, Gomendio M, Roldan ER, Dobrinski I.Xenografting of testis tissue from immature males from several mammalian species to immunodeficient mouse hosts results in production of fertilization-competent sperm. However, the efficiency of testis tissue xenografting from adult donors has not been critically evaluated. Testis tissue xenografting from sexually mature animals could provide an option to preserve the genetic material from valuable males when semen for cryopreservation cannot be collected. To assess the potential use of this technique for adult individuals, testes from adult animals of six species (pig, goat, cattle, donkey, h...
Raudsepp T, Chowdhary BP.The pseudoautosomal region (PAR) is a genomic segment on mammalian sex chromosomes where sequence homology mimics that seen between autosomal homologues. The region is essential for pairing and proper segregation of sex chromosomes during male meiosis. As yet, only human/chimp and mouse PARs have been characterized. The two groups of species differ dramatically in gene content and size of the PAR and therefore do not provide clues about the likely evolution and constitution of PAR among mammals. Here we characterize the equine PAR by i) isolating and arranging 71 BACs containing 129 markers (1...
Steiner CC, Ryder OA.Prdm9 (Meisetz) is the first speciation gene discovered in vertebrates conferring reproductive isolation. This locus encodes a meiosis-specific histone H3 methyltransferase that specifies meiotic recombination hotspots during gametogenesis. Allelic differences in Prdm9, characterized for a variable number of zinc finger (ZF) domains, have been associated with hybrid sterility in male house mice via spermatogenic failure at the pachytene stage. The mule, a classic example of hybrid sterility in mammals also exhibits a similar spermatogenesis breakdown, making Prdm9 an interesting candidate to e...
Huang J, Zhao Y, Bai D, Shiraigol W, Li B, Yang L, Wu J, Bao W, Ren X, Jin B, Zhao Q, Li A, Bao S, Bao W, Xing Z, An A, Gao Y, Wei R, Bao Y, Bao T....The donkey, like the horse, is a promising model for exploring karyotypic instability. We report the de novo whole-genome assemblies of the donkey and the Asiatic wild ass. Our results reflect the distinct characteristics of donkeys, including more effective energy metabolism and better immunity than horses. The donkey shows a steady demographic trajectory. We detected abundant satellite sequences in some inactive centromere regions but not in neocentromere regions, while ribosomal RNAs frequently emerged in neocentromere regions but not in the obsolete centromere regions. Expanded miRNA famil...
Li B, He X, Zhao Y, Bai D, Du M, Song L, Liu Z, Yin Z, Manglai D.Horse testis development and spermatogenesis are complex physiological processes. To study these processes, three immature and three mature testes were collected from the Mongolian horse, and six libraries were established using high-throughput RNA sequencing technology (RNA-Seq) to screen for genes related to testis development and spermatogenesis. A total of 16,237 upregulated genes and 8,641 downregulated genes were detected in the testis of the Mongolian horse. These genes play important roles in different developmental stages of spermatogenesis and testicular development. Five genes with ...
Hinrichs K.There is currently much interest in assisted reproduction techniques in the horse, however, many aspects of oocyte maturation, fertilization, and embryo development in the horse differ from those in other species. Because of the close attachment of the equine oocyte to the follicle wall, scraping of the follicle is the most effective method for oocyte recovery. A notable feature of equine oocytes is that those with expanded cumuli (Ex oocytes), which originate from atretic follicles, have higher meiotic competence (ability to mature to metaphase II in vitro) than do oocytes with compact cumuli...
Hinrichs K, Choi YH, Love LB, Varner DD, Love CC, Walckenaer BE.We evaluated the relationship of initial chromatin configuration to time of oocyte recovery and to nuclear maturation after culture in horse oocytes having compact (Cp) and expanded (Ex) cumuli. In addition, we evaluated the effect of oocyte type, time of recovery, and duration of culture on blastocyst development after intracytoplasmic sperm injection. In oocytes collected within 1 h of slaughter, fibrillar and intermediate chromatin configurations were more prevalent in Cp than in Ex oocytes (68% and 12%, respectively). In Cp oocytes collected after a 5- to 9-h delay, the proportions in the ...
Beeson SK, Mickelson JR, McCue ME.Total genetic map length and local recombination landscapes typically vary within and across populations. As a first step to understanding the recombination landscape in the domestic horse, we calculated population recombination rates and identified likely recombination hotspots using approximately 1.8 million SNP genotypes for 485 horses from 32 distinct breeds. The resulting breed-averaged recombination map spans 2.36 Gb and accounts for 2939.07 cM. Recombination hotspots occur once per 23.8 Mb on average and account for ∼9% of the physical map length. Regions with elevated recombination r...
Rizzo M, Ducheyne KD, Deelen C, Beitsma M, Cristarella S, Quartuccio M, Stout TAE, de Ruijter-Villani M.Advanced mare age is associated with declining fertility and an increased risk of early pregnancy loss. Compromised oocyte quality is probably the primary reason for reduced fertility, but the defects predisposing to embryonic death are unknown. In women, advanced age predisposes to chromosome segregation errors during meiosis, which lead to embryonic aneuploidy and a heightened risk of miscarriage. Objective: To evaluate the effect of advanced mare age on chromosome alignment and meiotic spindle morphology in in vitro-matured (IVM) oocytes. Methods: Morphometric and morphological analysis. M...
Torner H, Alm H, Kanitz W, Goellnitz K, Becker F, Poehland R, Bruessow KP, Tuchscherer A.The aim of this investigation was to examine the chromatin configuration of the nucleus, pattern of mitochondrial aggregation and mitochondrial activity in parallel studies in the same horse oocytes. Horse oocytes recovered by ultrasound-guided follicle aspiration in vivo were classified according to two main initial cumulus morphologies as having compact or expanded cumulus. The percentage of oocytes with a diplotene meiotic configuration at the time of recovery from the follicles was highest in compact oocytes. Oocytes with expanded cumulus layers at the time of recovery matured more rapidly...
Hinrichs K, Schmidt AL.Horse oocytes were collected from an abattoir over a 15-mo period. After classification of follicle size and cumulus morphology, oocytes were either fixed immediately (0 h) or matured in vitro (24 h). There was no effect of season on the number of antral follicles present on the ovaries, or on oocyte maturation rate for any class of oocyte. The proportion of oocytes having condensed chromatin at 0 h increased with increasing follicle size. The oocyte maturation rate also increased with follicle size, and for follicles </= 20-mm diameter, was higher for oocytes initially having expanded cumu...
Tharasanit T, Colleoni S, Galli C, Colenbrander B, Stout TA.Vitrifying oocytes is a potentially valuable means of preserving the female germ line, but significantly compromises oocyte developmental competence. This study examined the hypothesis that the cumulus complex protects the oocyte during vitrification. Vitrified-warmed immature cumulus oocyte complexes (COCs) were labelled with a plasma membrane impermeant DNA marker (ethidium homodimer-1) to examine the percentage and location of dead cumulus cells, and to investigate the effect of the proportion of dead cells (+1,+2 or +3) on the success of in vitro maturation (IVM). Further, oocytes were lab...
Belin F, Goudet G, Duchamp G, Gérard N.The objective of the present study was to determine the changes in follicular fluid steroid concentrations and in granulosa cell steroidogenic enzyme expression during the follicular phase, in relation to follicular size and physiological status in the mare. Follicular fluid and follicular cells were recovered by ultrasound-guided follicular punctures either around the time of emergence of the dominant follicle, at the end of the dominant follicle growth, or at the preovulatory stage, after injection of gonadotropin to induce ovulation. Cellular relative amounts of steroidogenic acute regulato...
Franciosi F, Lodde V, Goudet G, Duchamp G, Deleuze S, Douet C, Tessaro I, Luciano AM.Epigenetic modifications are established during gametogenesis and preimplantation embryonic development. Any disturbance of the normal natural environment during these critical phases could cause alterations of the epigenetic signature. Histone acetylation is an important epigenetic modification involved in the regulation of chromatin organization and gene expression. The present study was aimed to determine whether the proper establishment of post-translational histone H4 acetylation at lysine 8 (AcH4K8), 12 (AcH4K12) and 16 (AcH4K16) of equine oocytes is adversely affected during in vitro ma...
Johnson L, Blanchard TL, Varner DD, Scrutchfield WL.Spermatogenesis is a process of division and differentiation by which spermatozoa are produced in seminiferous tubules. Seminiferous tubules are composed of somatic cells (myoid cells and Sertoli cells) and germ cells (spermatogonia, spermatocytes, and spermatids). Activities of these three germ cells divide spermatogenesis into spermatocytogenesis, meiosis, and spermiogenesis, respectively. Spermatocytogenesis involves mitotic cell division to increase the yield of spermatogenesis and to produce stem cells and primary spermatocytes. Meiosis involves duplication and exchange of genetic materia...
Rizzo M, du Preez N, Ducheyne KD, Deelen C, Beitsma MM, Stout TAE, de Ruijter-Villani M.Aneuploidy of meiotic origin is a major contributor to age-related subfertility and an increased risk of miscarriage in women. Although age-related aneuploidy has been studied in rodents, the mare may be a more appropriate animal model to study reproductive aging. Similar to women, aged mares show reduced fertility and an increased incidence of early pregnancy loss; however, it is not known whether aging predisposes to aneuploidy in equine oocytes. We evaluated the effect of advanced mare age on (1) gene expression for cohesin components, (2) incidence of aneuploidy and (3) chromosome centrome...
Centromeres exert an inhibitory effect on meiotic recombination, but the possible contribution of satellite DNA to this "centromere effect" is under debate. In the horse, satellite DNA is present at all centromeres with the exception of the one from chromosome 11. This organization of centromeres allowed us to investigate the role of satellite DNA on recombination suppression in horse spermatocytes at the stage of pachytene. To this aim we analysed the distribution of the MLH1 protein, marker of recombination foci, relative to CENP-A, marker of centromeric function. We demonstrated that the sa...
Baumann C, Daly CM, McDonnell SM, Viveiros MM, De La Fuente R.Pairing of the sex chromosomes during mammalian meiosis is characterized by the formation of a unique heterochromatin structure at the XY body. The mechanisms underlying the formation of this nuclear domain are reportedly highly conserved from marsupials to mammals. In this study, we demonstrate that in contrast to all eutherian species studied to date, partial synapsis of the heterologous sex chromosomes during pachytene stage in the horse is not associated with the formation of a typical macrochromatin domain at the XY body. While phosphorylated histone H2AX (γH2AX) and macroH2A1.2 are pres...
Goudet G, Bézard J, Duchamp G, Gérard N, Palmer E.Equine oocyte competence after in vitro maturation (IVM) was investigated in terms of the diameter of the follicle of origin and the stage of the estrous cycle, with three criteria of maturation: nuclear stage after DNA Hoechst staining, meiotic spindle morphology after tubulin immunocytochemical staining, and cortical granule localization after lectin labeling. Seven successive in vivo ultrasound-guided follicular punctures were performed on 10 cyclic saddle mares, alternatively at the end of the follicular phase (after induction of ovulation with a gonadotropin injection) and in midluteal ph...
Dell'Aquila ME, Albrizio M, Maritato F, Minoia P, Hinrichs K.Follicle atresia and granulosa cell apoptosis may be related to oocyte meiotic and developmental competence. We analyzed the relationships among granulosa cell apoptosis, initial cumulus morphology, oocyte nuclear maturation in vitro, and pronucleus formation after intracytoplasmic sperm injection (ICSI) in the horse. For each follicle, the size was measured and granulosa cells were used for DNA laddering analysis. Oocytes were evaluated for cumulus morphology, cultured for in vitro maturation, and submitted to ICSI. Apoptosis was categorized as absent, intermediate, or advanced according to t...
Colleoni S, Luciano AM, Gandolfi F.Horse is a seasonal breeder and information on oocyte quality outside the breeding season is very limited. Ovaries obtained at the slaughterhouse are a convenient but often limited source of oocytes in this species. As the low quantity of ovaries leads to an intensive use of all available material, it would be useful to know whether ovaries collected during the non-breeding season are suitable for in vitro maturation (IVM). In an attempt to characterize the effect of season on oocyte quality, we investigated the permeability of the gap junctions (GJ) present between cumulus cells and oocytes b...
Hochi S, Kozawa M, Fujimoto T, Hondo E, Yamada J, Oguri N.The study was designed to examine the suitability of immature horse oocytes for vitrification. Immature oocytes derived from slaughtered horse ovaries were transferred to a vitrification solution (EFS; 40% ethylene glycol, 18% Ficoll, and 0.3 M sucrose in modified phosphate-buffered saline) directly (Groups 1 and 4) or were first exposed to 20% ethylene glycol solution for 10 min (Groups 2 and 5) or 20 min (Groups 3 and 6). Oocytes were handled at 20 degrees C (Groups 1, 2, and 3) or 30 degrees C (Groups 4, 5, and 6). After vitrification and warming, their viability was assessed by maturation ...
Ketchum CC, Larsen CD, McNeil A, Meyer-Ficca ML, Meyer RG.Chromatin remodeling during spermatogenesis culminates in the exchange of nucleosomes for transition proteins and protamines as an important part of spermatid development to give rise to healthy sperm. Comparative immunofluorescence analyses of equine and murine testis histological sections were used to characterize nucleoprotein exchange in the stallion. Histone H4 hyperacetylation is considered a key event of histone removal during the nucleoprotein transition to a protamine-based sperm chromatin structure. In the stallion, but not the mouse, H4 was already highly acetylated in lysine residu...
Ducheyne KD, Rizzo M, Daels PF, Stout TAE, de Ruijter-Villani M.Vitrified-warmed immature equine oocytes are able to complete the first meiotic division, but their subsequent developmental competence is compromised. Therefore, the present study investigated the effects of vitrifying immature horse oocytes on the chromosome and spindle configuration after IVM. Cumulus-oocytes complexes (COCs) were collected and divided into two groups based on mare age (young ≤14 years; old ≥16 years). COCs were then either directly matured invitro or vitrified and warmed before IVM. Spindle morphology and chromosome alignment within MII stage oocytes were assessed usin...
