Structure of the nucleoli in the spermatocytes of three canid species

The nucleolus is a structure of the cell nucleus associated mainly with ribosome biogenesis and indirectly responsible for protein biosynthesis. The nucleolus also plays a role in the regulation of cell growth and cell cycle progression, the detection and repair of DNA damage, and the export or degradation of mRNA. It is also involved in the most critical processes for the organism, such as ageing at the cellular level and broadly defined carcinogenesis. Analysis of the structure of nucleoli, which are the products of nucleolar organizer regions, can be an alternative source of information on the activity of rRNA-encoding genes. The material for the study was testes collected post mortem from sexually mature males of three canid species: silver fox (Vulpes vulpes), blue fox (Alopex lagopus) and Chinese raccoon dog (Nyctereutes procyonoides procyonoides). The morphology and morphometry of nucleoli identified in early primary spermatocytes were analysed. The values for all morphometric parameters of the spermatocyte nucleus were lowest for the silver fox and highest for the raccoon dog. In the case of nucleolus parameters, the lowest values were found in the raccoon dog and the lowest in the blue fox. The size of the nucleoli and spermatocyte nucleus proved to be a species-specific trait associated with the karyotype and number of nucleolar organizer regions in the species. The nucleolus is believed to play an important role in controlling meiosis. It is involved in preventing chromosome segregation during crossing over, and proteins associated with the nucleoli identify damaged synaptonemal complexes. Epigenetic regulations at the level of the nucleolus and rRNA genes remain a crucial subject of genetic research.