Role of HP1β during spermatogenesis and DNA replication.

Vijay Charaka,Raj K Pandita,Tej K Pandita,Clayton R Hunt,Anjana Tiwari

doi:10.1007/s00412-020-00739-4

Vijay Charaka, Raj K Pandita + Show 3 more

Open Access

https://doi.org/10.1007/s00412-020-00739-4

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Journal: Chromosoma	Publication Date: Jul 10, 2020
Citations: 6	License type: cc-by

Affiliation: Houston Methodist, Baylor College of Medicine

Abstract

Heterochromatin protein 1β (HP1β), encoded by the Cbx1 gene, has been functionally linked to chromatin condensation, transcriptional regulation, and DNA damage repair. Here we report that testis-specific Cbx1 conditional knockout (Cbx1 cKO) impairs male germ cell development in mice. Depletion of HP1β negatively affected sperm maturation and increased seminiferous tubule degeneration in Cbx1 cKO mice. In addition, the spermatogonia have elevated γ-H2AX foci levels as do Cbx1 deficient mouse embryonic fibroblasts (MEFs) as compared to wild-type (WT) control MEFs. The increase in γ-H2AX foci in proliferating Cbx1 cKO cells indicates defective replication-dependent DNA damage repair. Depletion or loss of HP1β from human cells and MEFs increased DNA replication fork stalling and firing of new origins of replication, indicating defective DNA synthesis. Taken together, these results suggest that loss of HP1β in proliferating cells leads to DNA replication defects with associated DNA damage that impact spermatogenesis.

Highlights

Meiosis generates haploid daughter cells and normal meiotic progression depends upon the fidelity of homologous chromosomes undergoing pairing, synapsis, recombination and proper segregation
Since loss of DNA repair proteins has been linked with germ cell loss and seminiferous tubules degeneracy (Gunes et al, 2015; Xu et al, 1996), we examined whether Cbx1 loss in testis is causing similar defects
Cbx1 testis specific KO mice showed increase in sperms lacking hook and folded banana shaped head morphology (Fig. 1h,I). These results suggest that HP1β plays a role till pachytene stage of meiosis, as we did not observe HP1β in either wild-type or Cbx1 testis specific conditional KO mouse testes post pachytene stage by immunofluorescence analysis (Fig. 2a)

Summary

Introduction

Meiosis generates haploid daughter cells and normal meiotic progression depends upon the fidelity of homologous chromosomes undergoing pairing, synapsis, recombination and proper segregation. DNA synthesis with proper fidelity is essential for repair of programmed DNA double strand breaks (DSBs) that are essential for chromosome dynamics in meiotic prophase I. In dividing cells HR predominantly occurs in mitotic S phase cells to maintain DNA fidelity During meiosis phase 1 the many double strand breaks generated during crossover are repaired by HR (Cohen and Pollard, 2001; Roeder, 1997). We reported that Cbx1-/- MEFs have increased genomic instability (Aucott et al, 2008) To circumvent this Cbx1-/- perinatal lethality, we crossed Cbx1f/f mice with Str Cre+/- mice to generate mice with testis germ cell Cbx deletion. Cbx loss in testis arrested spermatogonia cells at spermatogonia B stage and increased basal level DNA damage. Damage during the early stages of spermatogenesis correlated with decreased sperm production, which caused a subfertility phenotype

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