Deletion of Mgat2 in Spermatogonia Blocks Spermatogenesis

Identifying factors required for spermatogenesis is important for understanding mechanisms of male fertility. Inactivation of the Mgat1 or Man2a2 gene leads to a block in spermatogenesis causing infertility in male mice. In both cases multi-nucleated germ cells (MNC) are formed and there are no sperm in the epididymis. MGAT1 GlcNAc-transferase initiates complex N-glycan synthesis and MAN2A2 mannosidase generates the substrate for MGAT2 GlcNAc-transferase which transfers GlcNAc to form a biantennary complex N-glycan. Deletion of Mgat2 can leave its substrate, a hybrid N-glycan terminating in a single GlcNAc, to accumulate or the single GlcNAc may be extended to with Gal and GlcNAc to form polylactosamine. In this paper we show that conditional deletion of Mgat2 in spermatogonia via Stra8-iCre caused a block in spermatogenesis prior to the formation of round spermatids. This phenotype differs from deletion of Mgat1 by Stra8-iCre which generates MNC of round and elongated spermatids. In addition, RNA-seq analysis of germ cells prepared at 15 days after birth revealed a unique transcriptomic landscape in Mgat2[-/-] germ cells. Bioinformatic analyses predicted potential roles for ERK and AKT activities which were validated by western analyses. By contrast, Mgat1[-/-] germ cells have reduced ERK activity and unchanged AKT activity. Therefore, the defective spermatogenesis observed following removal of MGAT1 or MGAT2 must arise from the different immature N-glycans that accumulate rather than from the loss of complex N-glycans which is common to both.