The mechanisms determining the nucleolar-organizing regions inactivation of domestic horse chromosomes.

This study investigates the genetic mechanisms behind the variation found in the transcriptional activity of rDNA in horse chromosomes, specifically in nucleolar-organizing regions (NORs). The findings suggest that this variation is due to a combination of factors including the number of rDNA copies, DNA methylation, and the location of ribosomal DNA loci in telomeric regions.

Objective of the Study

• The main purpose of the research was to understand the possible genetic mechanisms that regulate the polymorphism of the nucleolar-organizing regions (NORs) in the domestic horse chromosomes. For this purpose, the researchers utilized various molecular cytogenetic analysis techniques specifically on Hucul horses.

Methodology of the Study

• The investigation involved several advanced molecular cytogenetic analysis methods, including fluorescence in situ hybridization (FISH), telomere primed in situ synthesis (PRINS), in situ nick-translation with HpaII, silver staining (AgNOR), and C-banding technique (CBG).

Key Findings

• Analysis revealed that changes in the number and size of silver deposits are associated with variations in the number of rDNA copies, the methylation of DNA, and the placement of ribosomal DNA loci in telomeric regions. These elements collectively contribute to the polymorphism or genetic variation of the NORs in horse chromosomes.
• The study also found that specific chromosome pairs, namely 28 and 31, exhibit a higher variation in the number of NORs. This observation leads to a better understanding of how specific chromosomes may have inherently greater variability due to their genetic makeup.

Significance of the Research

• The study provides essential insights into the genetic mechanics of the transcriptional activity of rDNA in horse chromosomes, notably in the nucleolar-organizing regions (NORs). The knowledge derived from this study can meaningfully contribute to genetic research, particularly for breed selection and disease detection in horses.