Gap junctions mediate discrete regulatory steps during fly spermatogenesis

Abstract

Gametogenesis requires coordinated signaling between germ cells and somatic cells. We previously showed that Gap junction (GJ)-mediated soma-germline communication is essential for fly spermatogenesis. Specifically, the GJ protein Innexin4/Zero population growth (Zpg) is necessary for somatic and germline stem cell maintenance and differentiation. It remains unknown how GJ-mediated signals regulate spermatogenesis or whether the function of these signals is restricted to the earliest stages of spermatogenesis. Here we carried out comprehensive structure/function analysis of Zpg using insights obtained from the protein structure of innexins to design mutations aimed at selectively perturbing different regulatory regions as well as the channel pore of Zpg. We identify the roles of various regulatory sites in Zpg in the assembly and maintenance of GJs at the plasma membrane. Moreover, mutations designed to selectively disrupt, based on size and charge, the passage of cargos through the Zpg channel pore, blocked different stages of spermatogenesis. Mutations were identified that progressed through early germline and soma development, but exhibited defects in entry to meiosis or sperm individualisation, resulting in reduced fertility or sterility. Our work shows that specific signals that pass through GJs regulate the transition between different stages of gametogenesis.

Identification of testis development-related genes by combining Iso-Seq and RNA-Seq in Zeugodacus tau

“…Previous studies have suggested a role of gap junction components in regulating soma-germline communication ( Starich et al, 2014 ). When gap junction between the soma and germline is disrupted, germline differentiation is blocked, and germline stem cells are not maintained ( Smendziuk et al, 2015 ; Huynh et al, 2022 ). Gap junctions are composed of innexin proteins in invertebrates ( Stebbings et al, 2002 ; Bauer et al, 2005 ; Beyer and Berthoud, 2018 ).…”

Gap junction and amino acid import in somatic cells promote germ cell growth

“…Moreover, Inx4 and Inx2 form gap junctions in the testis where they are required at different steps of sperm development (27,32,33).…”

“…such as the stretching of anterior follicle cells and the migration of border cells during stage 9 (6,29). Moreover, Inx4 and Inx2 form gap junctions in the testis where they are required at different steps of sperm development (27,32,33).…”