Tandem Repeat-Based Probes Support the Loop Model of Pericentromere Packing.

Constitutive heterochromatin is the most mysterious part of the eukaryotic genome. It forms vital chromosome regions such as the centromeric and the pericentromeric ones. The main component of heterochromatic regions are tandem repeats (TR), and their specific organization complicates assembly, annotation, and mapping of these regions. Unannotated and unmapped TR arrays are still present in database contigs. In this study, we used a set of TR in the genomes of the pig (Sus scrofa) and the Chinese hamster (Cricetulus griseus) identified with the help of bioinformatics techniques and determined the specificity of the designed probes. The signal of the 4 pig TR probes in spermatogenic cells was often ring-shaped, especially in primary spermatocytes. The rings were located in the regions relatively weakly stained with DAPI. The unique assembly of the centromeric region was traced using the hamster meiotic chromosomes. The probe specific to chromosome 5 was used. Two signals, arranged as rings, were seen at the pachytene stage, similar to those in the pig spermatogenic cells. In the spermatogenic cells of both pig and hamster, the rings appeared on the chromosomes with pericentromeric TR probes. Our observations support the loop model of the centromeric region, the size of the loops being about 50 kb.

Tandem Repeat Diversity in Two Closely Related Hamster Species-The Chinese Hamster (Cricetulus griseus) and Striped Hamster (Cricetulus barabensis).

The Chinese hamster (Cricetulus griseus) and striped hamster (Cricetulus barabensis) are very closely related species with similar karyotypes. The karyotypes differ from each other by one Robertsonian rearrangement and X-chromosome morphology. The level of the tandem repeat (TR) sequences' evolutional variability is high. The aim of the current work was to trace the TR distribution on the chromosomes of two very closely related species. The striped hamster genome has not yet been sequenced. We classified the Chinese hamster TR in the assemblies available and then compared the mode of the TR distribution in closely related species. Chinese and striped hamsters are separate species due to the relative species specificity of Chinese hamster TR and prominent differences in the TR distribution in both species. The TR variation observed within homologous striped hamster chromosomes is caused by a lack of inbreeding in natural populations. The set of TR tested could be used to examine the CHO lines' instability that has been observed in heterochromatic regions.