TheDrosophilachromosomal protein Mst77F is processed to generate an essential component of mature sperm chromatin

Abstract

In most animals, the bulk of sperm DNA is packaged with sperm nuclear basic proteins (SNBPs), a diverse group of highly basic chromosomal proteins notably comprising mammalian protamines. The replacement of histones with SNBPs during spermiogenesis allows sperm DNA to reach an extreme level of compaction, but little is known about how SNBPs actually function in vivo. Mst77F is a Drosophila SNBP with unique DNA condensation properties in vitro, but its role during spermiogenesis remains unclear. Here, we show that Mst77F is required for the compaction of sperm DNA and the production of mature sperm, through its cooperation with protamine-like proteins Mst35Ba/b. We demonstrate that Mst77F is incorporated in spermatid chromatin as a precursor protein, which is subsequently processed through the proteolysis of its N-terminus. The cleavage of Mst77F is very similar to the processing of protamine P2 during human spermiogenesis and notably leaves the cysteine residues in the mature protein intact, suggesting that they participate in the formation of disulfide cross-links. Despite the rapid evolution of SNBPs, sperm chromatin condensation thus involves remarkably convergent mechanisms in distantly related animals.

Evolutionary origins and diversification of testis-specific short histone H2A variants in mammals

“…Since the only function demonstrated for short H2A variants is in protamine deposition (Barral, et al 2017), we speculate that the functional constraints acting on the short histone variants may be similar to those that act on protamines, which are themselves considered to be among the fastest-evolving proteins in mammalian genomes (Retief and Dixon 1993;Wyckoff, et al 2000;Torgerson, et al 2002;Martin-Coello, et al 2009). Although the high dN/dS values of protamine proteins may be artificially inflated due to selective pressure to maintain high basic amino acid content across the whole protein (Rooney and Zhang 1999;Clark and Civetta 2000;Rooney, et al 2000), these arguments cannot explain other rapidly-evolving sperm-specific DNA-packaging proteins in animal genomes (Wyckoff, et al 2000;Kimura and Loppin 2016).…”

salto/CG13164is required for sperm head morphogenesis inDrosophila

“…Slides were mounted using Vectashield containing Hoechst (1:1000). Antibodies used were the following: guinea pig anti-Asterless (1/30,000; gift from C. Rogers, University of Arizona, Tucson, AZ; Klebba et al , 2013); mouse Axo49 anti–polyglycylated tubulin (1/100; provided by N. Levilliers, Laboratoire de Biologie Cellulaire 4, CNRS, Université Paris-Sud, Orsay, France); rabbit anti-Tpl94D (1/100) and Mst35Bb (1/200) kindly provided by B. Loppin, LBBE, CNRS UMR 5558 (Kimura and Loppin, 2016); mouse anti–alpha-tubulin DM1a (1/500) (Sigma Aldrich); mouse anti-Myosin VI/jaguar (1/200) (Kellerman and Miller, 1992), kindly provided by Stéphane Vincent (ENSL); rabbit anti-cleaved caspase 3 (CC3) (1/100) (Cell Signaling); guinea pig anti-Soti (1/100) and rabbit anti-dBruce (1/500, kindly provided by E. Arama); mouse anti-LaminC (1/25) (DHSB).…”

Identification of a complex population of chromatin-associated proteins in the European sea bass (Dicentrarchus labrax) sperm

“…Similarly, the differential poising of the sperm chromatin is also present in vertebrate species which do not express protamines, but that organize its full complement of the sperm DNA with histones and histone variants, containing histone modifications, and other chromatin marks (Wu et al 2011). Furthermore, the presence of relevant chromatin-associated proteins in sperm has also been described in invertebrates such as Drosophila melanogaster (Dorus et al 2008;Elnfati et al 2015;Kimura and Loppin 2016;Pimenta-Marques et al 2016).…”

“…2008; Elnfati et al 2015;Gärtner et al 2015;Kimura and Loppin 2016;Rivera-Casas et al 2017), as well as from algae and other eukaryotes (Kasinsky et al 2014). It has been proposed that this sperm chromatin condensation by protamines may serve (1) to reduce the size of the sperm cell nuclei, allowing the spermatozoon to adopt a hydrodynamic shape so that it can swim faster and (2) to protect the paternal genome during its journey and delivery to the oocyte to form the zygote and final embryo (Oliva and Dixon 1991;Oliva 2006;Balhorn 2007;Björndahl and Kvist 2011).…”

“…In some cases, there is evidence indicating the presence of a minor proportion of proteins with an electrophoretic migration profile similar to that of histones, coexisting with a major proportion of protamines in the mature sperm cells (Saperas et al 1993(Saperas et al , 1994Zilli et al 2005;Kurtz et al 2009). Furthermore, proteomic studies on the seminal proteins from different fish species and from other vertebrates and invertebrates are now available (Dorus et al 2008(Dorus et al , 2012Awe and Renkawitz-Pohl 2010;Oliva 2012;Elnfati et al 2015;Gärtner et al 2015;Kimura and Loppin 2016). However, to our knowledge, only two studies have been performed so far to describe the proteomic composition of protamines-expressing teleost fish sperm.…”