SAT-031 Linking Gonadotropin-Regulated Testicular RNA Helicase (GRTH/DDX25) to Histone Ubiquitination Network and Acetylation During Spermiogenesis

Gonadotropin Regulated Testicular Helicase (GRTH/DDX25), a testis specific RNA helicase essential for the completion of spermatogenesis. Our early studies discovered a missense mutation (R242H) of GRTH gene in 5.8 % of a Japanese population with azoospermia. This mutation in COS-1 cells showed loss of the 61 kDa cytoplasmic phospho-species with preservation of the 56Kda nuclear non-phospho form of GRTH. Mice with knock-in (KI) of the human GRTH mutation, lack the phospho-form of GRTH, are sterile and lack sperm, with spermatogenic arrest at stage 8 of round spermatids. To determine the impact of phospho-GRTH on gene expression comparative studies of germ cells transcriptome profiles from WT and KI mice were conducted using Illumina RNA sequencing. RNA-Seq analysis revealed 1614 differentially expressed genes of which 886 down-regulated and 728 genes up-regulated genes. Gene Ontology analysis revealed several genes relevant to spermatogenesis, spermatid development and differentiation significantly downregulated. KEGG analysis showed genes related to Ubiquitin mediated proteolysis, protein processing in ER, RNA transport, Glycolysis pathways are down-regulated, and genes related to Focal adhesion and ECM interaction are up-regulated. RealTime-PCR analysis confirmed dramatic reduction in mRNA expression of ubiquitination related genes Ube2j1, Ube2k, Ube2w, Rnf8, Rnf133, Rnf138 and increased expression of Ccnd2, Col1a, Lamb1, Cav1, Igf1, Itga9 mRNA’s in KI mice compared to WT. Western blot analysis revealed marked reduction in protein expression of UBE2J1, RNF8, RNF138 (ubiquitination network), MOF (histone acetyltransferase) and their modified Histone substrates (H2AUb, H2BUb), as well as H4Ac, H4K16Ac in KI mice. Immunohistochemistry analysis showed significantly reduced expression of RNF8, MOF, H4Ac and H4K16Ac in round spermatids of KI mice compared to WT. In KI mice absence of phospho-GRTH impairs RNF8 and MOF dependent ubiquitination and acetylation of histones required for histone replacement, chromatin condensation and spermatid elongation during spermiogenesis which finally results in germ cell arrest in step 8 of round spermatids. Thus, we conclude that phospho-GRTH affects the network which is critical for the replacement of histones during spermiogenesis.