Neurofibromin haploinsufficiency results in altered spermatogenesis in a mouse model of neurofibromatosis type 1

Abstract

The fertility of men with neurofibromatosis 1 (NF1) is reduced. Despite this observation, gonadal function has not been examined in patients with NF1. In order to assess the role of reduced neurofibromin in the testes, we examined testicular morphology and function in an Nf1+/- mouse model. We found that although Nf1+/- male mice are able to reproduce, they have significantly fewer pups per litter than Nf1+/+ control males. Reduced fertility in Nf1+/- male mice is associated with disorganization of the seminiferous epithelium, with exfoliation of germ cells and immature spermatids into the tubule lumen. Morphometric analysis shows that these alterations are associated with decreased Leydig cell numbers and increased spermatid cell numbers. We hypothesized that hyper-activation of Ras in Nf1+/- males affects ectoplasmic specialization, a Sertoli-spermatid adherens junction involved in spermiation. Consistent with this idea, we found increased expression of phosphorylated ERK, a downstream effector of Ras that has been shown to alter ectoplasmic specialization, in Nf1+/- males in comparison to control Nf1+/+ littermates. These data demonstrate that neurofibromin haploinsufficiency impairs spermatogenesis and fertility in a mouse model of NF1.

Infertility-Causing Haploinsufficiency Reveals TRIM28/KAP1 Requirement in Spermatogonia

“…Haploinsufficiency-a mechanism by which a loss-of-function mutation leaves only one functional copy of a gene and so leads to insufficient gene product (Deutschbauer et al, 2005)-is a major cause for developmental disorders (Kurotaki et al, 2002;Meechan et al, 2007), including male infertility (Chohan et al, 2018;Zhang et al, 2004). Haploinsufficiency phenotypes typically involve key genes that encode transcription factors and/or function in developmental processes (Dang et al, 2008;Deutschbauer et al, 2005).…”

A nuclear role for the Argonaute protein AGO2 in mammalian gametogenesis

“…The set of head morphology defects observed in Ago2 cKO sperm parallels the defects expected following depletion of several of the proteins downregulated in Ago2 cKO post-meiotic germ cells, including HMGB2, YBX2, and PTBP2 (Catena et al, 2006;Hannigan et al, 2018;Lorès et al, 2018;Snyder et al, 2015). Further, at least two of the transcription factors with binding motifs enriched among the set of dual AGO2 ChIP and CLIP targets (NF1 and STAT4; Figure 5J) are known to regulate sperm head formation (Chohan et al, 2018;Herrada and Wolgemuth, 1997). Phenotype enrichment analysis (Weng and Liao, 2017) confirmed that downregulated DEPs were statistically significantly (adjusted P-value ≤ 0.05) enriched for abnormal male germ cell morphology and other reproductive phenotypes including male infertility and arrest of spermatogenesis.…”

Widespread association of the Argonaute protein AGO2 with meiotic chromatin suggests a distinct nuclear function in mammalian male reproduction

“…Further, at least two of the transcription factors with binding motifs enriched among the set of dual AGO2 ChIP and eCLIP targets (NF1 and STAT4) ( Fig. 3 K) are known to regulate sperm head formation ( Herrada and Wolgemuth 1997 ; Chohan et al 2018 ). Phenotype enrichment analysis ( Weng and Liao 2017 ) confirmed that down-regulated DEPs were statistically significantly (adjusted P -value ≤ 0.05) enriched for abnormal male germ cell morphology and male infertility.…”