[Analysis of the distribution of ribosomal RNA genes on chromosomes of the domestic horse (Equus caballus) using fluorescent in situ hybridization].

The researchers studied the distribution of ribosomal RNA genes across chromosomes of 26 domestic horses from five breeds by using a technique known as fluorescence in situ hybridization (FISH) alongside simultaneous R-banding. They found gene loci coding for rRNA on several chromosomes and discovered a previously undetected nucleolar organizer region (NOR) on chromosome 27. They also found individual and interchromosomal variations in NORs.

Methodology

• The study used a method known as fluorescence in situ hybridization (FISH), a laboratory technique for detecting the presence or location of specific DNA sequences on chromosomes. This technique was combined with R-banding, a chromosome-staining process that highlights certain bands or regions of the chromosomes.
• The sample for the study consisted of 26 horses from five different breeds. The study specifically aimed to determine the distribution of blocks of ribosomal RNA genes along the horses’ metaphase chromosomes.

Findings

• The gene loci coding for ribosomal RNA (rRNA) were mapped to specific areas on several chromosomes: the area of secondary constriction on the short arm of chromosome 1 and the pericentromeric regions of chromosomes 27, 28, and 31.
• Interestingly, a nucleolar organizer region (NOR) was detected on chromosome 27. This indicates the presence of a region of the chromosome responsible for initiating formation of the nucleolus, a structure within intact cell nuclei where ribosomal RNA is produced.
• The research also revealed interindividual (between individual horses) and interchromosomal (between different chromosomes in the same horse) NOR polymorphism. This refers to a variation in the DNA sequence at a particular spot on the genome, indicating that NOR sequences can vary both between individuals and on different chromosomes within the same individual.
• This NOR variation was detected through the use of a semiquantitative score estimation method for fluorescence hybridization signals, providing a visual representation of DNA sequences under examination.

Significance of the Study

• This research may contribute to a better understanding of the genetic variety in horses and possible associations between certain traits or ailments and specific genetic markers.
• The discovery of a previously undefined NOR on chromosome 27 may have significant implications for our understanding of genetic regulation and cellular function in horses.
• The observed interindividual and interchromosomal polymorphism may offer insights into genetic diversity and chromosome evolution in the species.