Loss of GGN Leads to Pre-Implantation Embryonic Lethality and Compromised Male Meiotic DNA Double Strand Break Repair in the Mouse

Abstract

The integrity of male germ cell genome is critical for the correct progression of spermatogenesis, successful fertilization, and proper development of the offspring. Several DNA repair pathways exist in male germ cells. However, unlike somatic cells, key components of such pathways remain largely unidentified. Gametogenetin (GGN) is a testis-enriched protein that has been shown to bind to the DNA repair protein FANCL via yeast-two-hybrid assays. This finding and its testis-enriched expression pattern raise the possibility that GGN plays a role in DNA repair during spermatogenesis. Herein we demonstrated that the largest isoform GGN1 interacted with components of DNA repair machinery in the mouse testis. In addition to FANCL, GGN1 interacted with the critical component of the Fanconi Anemia (FA) pathway FANCD2 and a downstream component of the BRCA pathway, BRCC36. To define the physiological function of GGN, we generated a Ggn null mouse line. A complete loss of GGN resulted in embryonic lethality at the very earliest period of pre-implantation development, with no viable blastocysts observed. This finding was consistent with the observation that Ggn mRNA was also expressed in lower levels in the oocyte and pre-implantation embryos. Moreover, pachytene spermatocytes of the Ggn heterozygous knockout mice showed an increased incidence of unrepaired DNA double strand breaks (DSBs). Together, our results suggest that GGN plays a role in male meiotic DSB repair and is absolutely required for the survival of pre-implantation embryos.

Ablation of Ggnbp2 impairs meiotic DNA double‐strand break repair during spermatogenesis in mice

“…It has been reported that GGNBP2 interacts with testicular proteins, GGN1, GGNBP1, CRISP2 and OAZ3 26, 28, 29, 30. Reciprocal immunoprecipitation (IP) with GGN (Figure 3A) and GGNBP2 (Figure 3B) antibodies demonstrated that GGN1 and GGNBP2 formed a protein complex in the testis.…”

“…GGN1, in turn, recruits other factors to proper positions on the chromosome to repair DSBs. Jamsai et al30 proposed that GGN1 played a role in meiotic DSB repair in the testis via its connection with the factors such as FANCL and BRCC36 of Fanconi anaemia (FA) and breast cancer (BRCA) pathways to efficiently repair DNA DSBs. Indeed, these proteins have been established to form a complex by binding with GGN1 25, 30.…”

“…Jamsai et al30 proposed that GGN1 played a role in meiotic DSB repair in the testis via its connection with the factors such as FANCL and BRCC36 of Fanconi anaemia (FA) and breast cancer (BRCA) pathways to efficiently repair DNA DSBs. Indeed, these proteins have been established to form a complex by binding with GGN1 25, 30. More studies will help us to understand the involvement of GGNBP2 and GGN1 in the process of DNA DSB repair and to elucidate the nature of the interaction among GGNBP2, GGN1, FA and BRCA proteins to control meiotic prophase progression.…”

“…The largest variant GGN1 is demonstrated to be the predominant form in the testis and localizes in spermatocytes, spermatids and spermatozoa but not in spermatogonia in mouse and human testes 25, 26, 27. GGN1 is identified to interact with various proteins, which include FANCL, FANCD2, BRCC36, OAZ3, CRISP2, GGNBP1 and GGNBP2 26, 28, 29, 30. As such, GGN1 is proposed to play a role in meiosis involving in DNA DSB repair25, 27, 30 as well as sperm tail development and/or motility in the testis 29.…”

Deregulation of Sertoli and Leydig cells function in patients with Klinefelter syndrome as evidenced by testis transcriptome analysis

“…CLDN5 and CLDN16 encode for components of tight junction strands and their overexpression could reflect either a protective mechanism of response against the testicular microenvironment disruption or inflammation response, or the presence of immature SCs [32]. FANCD2 product regulates in testis the seminiferous tubules maintenance, and its downexpression has been associated with reduction of germ cells number [33]. CLU is synthesized by SCs and regulates the germ cells proliferation and differentiation and its down-expression could be the consequence of germ cells absence.…”