TY - JOUR

T1 - Some Peculiarities of MLH1 Foci Distribution in Common Degu (Octodon degus, Rodentia: Octodontidae) Chromosomes: Presence in Pericentromeric Regions and Absence in XY

AU - Bikchurina, Tatiana

AU - Grishko, Ekaterina

AU - Odnoprienko, Daria

AU - Borodin, Pavel

N1 - The study was supported by the Ministry of Education and Science of the Russian Federation (Grant No. FWNR-2022-0015 and FSUS-2024-0018). The funders had no role in the design, data collection, data analysis, and reporting of this study.

PY - 2025/4/16

Y1 - 2025/4/16

N2 - Introduction: Meiotic recombination is one of the major sources of genetic diversity. Understanding the cytogenetic basis for recombination rate alterations is essential to explain the patterns of variation observed between different groups of species. Common degu (Octodon degus) is a South American rodent of the speciose and highly chromosomal variable Ctenohystrica clade, on which relatively few cytogenetic studies have been carried out. It has a mostly bi-armed karyotype, making it an interesting model for cytogenetic research. Methods: Using immunolocalization of key meiotic proteins and electron microscopy in pachytene spermatocytes, we determined the frequency and distribution of recombination events along a number of chromosome bivalents and the characteristics of sex chromosome synapsis. Results: Recombination rate of common degu was the highest among the Hystricognathi species studied. In contrast to most mammals, no pronounced recombination peaks near the telomeres were observed in degu. We detected late recombination nodules in the pericentromeric regions of some bivalents, which is a highly extraordinary pattern due to the centromere effect. Within the heterochromatic blocks located on the chromosome arms and marked by H3K9me3, one of the major constitutive heterochromatin marks, we observed a significant decrease in recombination frequency. We describe for the first time the bridge between X and Y in the late pachytene stage in common degu and the absence of late MLH1-dependent recombination nodules in the sex bivalent. Conclusion: We can assume that the absence of H3K9me3 signaling at centromeres is unrelated to the presence of MLH1 near the centromere. Findings on potential achiasmatic meiosis in common degu were discussed in relation to sex chromosome evolution.

AB - Introduction: Meiotic recombination is one of the major sources of genetic diversity. Understanding the cytogenetic basis for recombination rate alterations is essential to explain the patterns of variation observed between different groups of species. Common degu (Octodon degus) is a South American rodent of the speciose and highly chromosomal variable Ctenohystrica clade, on which relatively few cytogenetic studies have been carried out. It has a mostly bi-armed karyotype, making it an interesting model for cytogenetic research. Methods: Using immunolocalization of key meiotic proteins and electron microscopy in pachytene spermatocytes, we determined the frequency and distribution of recombination events along a number of chromosome bivalents and the characteristics of sex chromosome synapsis. Results: Recombination rate of common degu was the highest among the Hystricognathi species studied. In contrast to most mammals, no pronounced recombination peaks near the telomeres were observed in degu. We detected late recombination nodules in the pericentromeric regions of some bivalents, which is a highly extraordinary pattern due to the centromere effect. Within the heterochromatic blocks located on the chromosome arms and marked by H3K9me3, one of the major constitutive heterochromatin marks, we observed a significant decrease in recombination frequency. We describe for the first time the bridge between X and Y in the late pachytene stage in common degu and the absence of late MLH1-dependent recombination nodules in the sex bivalent. Conclusion: We can assume that the absence of H3K9me3 signaling at centromeres is unrelated to the presence of MLH1 near the centromere. Findings on potential achiasmatic meiosis in common degu were discussed in relation to sex chromosome evolution.

KW - Centromere effect

KW - Common degu

KW - Sex bivalent

KW - · Recombination ·

KW - · Synaptonemal complex

UR - https://www.mendeley.com/catalogue/0c822bd4-d293-33b3-bc04-d3631bc9dee4/

UR - https://pubmed.ncbi.nlm.nih.gov/40239643/

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-105008540569&origin=inward&txGid=4686954b74dfe9179311e71e675a8436

U2 - 10.1159/000545928

DO - 10.1159/000545928

M3 - Article

C2 - 40239643

JO - Cytogenetic and Genome Research

JF - Cytogenetic and Genome Research

SN - 1424-8581

ER -