Three autosomal chromosome translocations associated with repeated early embryonic loss (REEL) in the domestic horse (Equus caballus).

This study examines three types of chromosome abnormalities found in Thoroughbred mares that have experienced frequent early embryonic loss, suggesting that these genetic irregularities might play a more significant role in mare fertility than previously thought and emphasizing the importance of karyotyping such horses for more effective reproductive management.

Understanding Chromosome Abnormalities in Mares

The research represents an exploration of three autosomal translocations within the chromosomes of Thoroughbred mares that continually experience REEL. These particular karyotypes are represented as 64,XX,t(1;21), 64,XX,t(16;22), and 64,XX,t(4;13).

• An autosomal translocation indicates a form of chromosomal abnormality where a segment of genetic material gets misplaced from one chromosome to another non-sex (autosomal) chromosome.
• Karyotypes designate the number and visual appearance of the chromosomes in the cell nuclei of an organism.

Determining Breakpoints

The study uses previous research and the latest horse genome sequence to identify genes around the translocation breakpoints which were then confirmed by fluorescence in situ hybridization (FISH).

• FISH is a molecular cytogenetic technique used to detect and localize specific DNA sequences on chromosomes. It was used to confirm whether the translocations were reciprocal, i.e., if genetic material exchange took place between the chromosomes.
• Two of the translocations were confirmed as reciprocal (64,XX,t(16;22) and 64,XX,t(4;13)), while one translocation (64,XX,t(1;21)) was determined as non-reciprocal.

Identifying Ancient Breakpoints

The study makes a noteworthy remark on the breakpoints on horse chromosomes 1 and 16. They suggest these locations to be ancient breakpoints – reused during equid evolution.

• These alleged ancient breakpoints correspond to the human chromosomes fusion boundaries – human chromosomes 10 and 15 on horse chromosome 1 and human chromosome 3p and 3q on horse chromosome 16.

Implication of the Findings

These discoveries insinuate that chromosome abnormalities might have a larger effect on mare fertility than previously estimated, making it crucial to karyotype mares suspect of being subfertile and exhibiting REEL for more successful breeding.

• Often, mares suffering from REEL might not be considered potential chromosome abnormality carriers, leading to overlooked treatment options and conclusions about the mares’ fertility status.