GASZ and mitofusin‐mediated mitochondrial functions are crucial for spermatogenesis

Abstract

Nuage is an electron-dense cytoplasmic structure in germ cells that contains ribonucleoproteins and participates in piRNA biosynthesis. Despite the observation that clustered mitochondria are associated with a specific type of nuage called intermitochondrial cement (pi-body), the importance of mitochondrial functions in nuage formation and spermatogenesis is yet to be determined. We show that a germ cell-specific protein GASZ contains a functional mitochondrial targeting signal and is largely localized at mitochondria both endogenously in germ cells and in somatic cells when ectopically expressed. In addition, GASZ interacts with itself at the outer membrane of mitochondria and promotes mitofusion in a mitofusin/MFN-dependent manner. In mice, deletion of the mitochondrial targeting signal reveals that mitochondrial localization of GASZ is essential for nuage formation, mitochondrial clustering, transposon repression, and spermatogenesis. MFN1 deficiency also leads to defects in mitochondrial activity and male infertility. Our data thus reveal a requirement for GASZ and MFNmediated mitofusion during spermatogenesis.

Germ granule-mediated RNA regulation in male germ cells

“…However, some proteins appear to be IMC specific (Chuma et al 2006, Hosokawa et al 2007, Ma et al 2009, Bao et al 2013b, Zhou et al 2014. For example, GASZ (germ cell-specific protein with four Ankyrin repeats, a sterile alpha motif and a basic leucine Zipper domain), localizes predominantly to the IMC (Ma et al 2009), which is largely explained by its functional mitochondrial targeting signal and its function in promoting mitofusion (Zhang et al 2016). Another mitochondria-interacting IMC protein is PLD6/ MitoPLD, a phospholipase that facilitates mitofusion, participates in nuage formation and piRNA biosynthesis during spermatogenesis (Huang et al 2011, Watanabe et al 2011.…”

“…In mouse, the 3′ trimming of piRNAs is predicted to follow a similar route and in fact, the mouse Papi homolog TDRD2/TDRKH was shown to be required for the production of correct size piRNAs (Saxe et al 2013). piRNA biogenesis is also dependent on mitochondrial membrane proteins GPAT2 and GASZ (Ma et al 2009, Shiromoto et al 2013, Zhang et al 2016. Trimmed piRNAs are finally 2′-O-methylated at their 3′ ends by HENMT1 resulting in primary piRNAs with a predominant preference for a 5′ uridine (Horwich et al 2007, Saito et al 2007, Lim et al 2015.…”

NRF1 coordinates with DNA methylation to regulate spermatogenesis

“…Mouse embryonic fibroblasts (MEFs), NIH3T3, 293T, and GC1 cells were cultured, transfected, or infected according to published protocols (7,9). All were originally from American Type Culture Collection (Manassas VA, USA), except the MEFs, which were made from mouse embryos at 13.5 dpc.…”

“…Among them, ankyrin repeat, sterile a-motif and basic leucine zipper domain-containing (ASZ)-1 protein is an important germ cell-specific protein that is first detected in postmigrating PGCs ;12.5 d postcoitum (dpc) (7) and is highly expressed in spermatocytes from adult testis (8). Previous reports have demonstrated that ASZ1 is localized at the mitochondrial outer membrane at nuage, a specialized electron-dense cytoplasmic structure, where it modulates piwi-interacting RNA biosynthesis in germ cells, probably through interaction with RNA-processing proteins, such as miwi-like (MILI) and DEAD-box 4 (DDX4) proteins (9,10). Either deletion of ASZ1 or mutation of its mitochondrial localization signal leads to male infertility in mice (9,10).…”

“…Previous reports have demonstrated that ASZ1 is localized at the mitochondrial outer membrane at nuage, a specialized electron-dense cytoplasmic structure, where it modulates piwi-interacting RNA biosynthesis in germ cells, probably through interaction with RNA-processing proteins, such as miwi-like (MILI) and DEAD-box 4 (DDX4) proteins (9,10). Either deletion of ASZ1 or mutation of its mitochondrial localization signal leads to male infertility in mice (9,10). Similarly, gene-knockout studies have revealed the essential roles and similar expression patterns of RNA-binding proteins such as deleted in azoospermia-like (DAZL), DDX25, and NANOS (Drosophila NOS homolog) family members in germ cell development (11)(12)(13)(14).…”