Sperm chromatin proteomics identifies evolutionarily conserved fertility factors

Abstract

Male infertility is a long-standing enigma of significant medical concern. The integrity of sperm chromatin is a clinical indicator of male fertility and in vitro fertilization potential: chromosome aneuploidy and DNA decondensation or damage are correlated with reproductive failure. Identifying conserved proteins important for sperm chromatin structure and packaging can reveal universal causes of infertility. Here we combine proteomics, cytology and functional analysis in Caenorhabditis elegans to identify spermatogenic chromatin-associated proteins that are important for fertility. Our strategy employed multiple steps: purification of chromatin from comparable meiotic cell types, namely those undergoing spermatogenesis or oogenesis; proteomic analysis by multidimensional protein identification technology (MudPIT) of factors that co-purify with chromatin; prioritization of sperm proteins based on abundance; and subtraction of common proteins to eliminate general chromatin and meiotic factors. Our approach reduced 1,099 proteins co-purified with spermatogenic chromatin, currently the most extensive catalogue, to 132 proteins for functional analysis. Reduction of gene function through RNA interference coupled with protein localization studies revealed conserved spermatogenesis-specific proteins vital for DNA compaction, chromosome segregation, and fertility. Unexpected roles in spermatogenesis were also detected for factors involved in other processes. Our strategy to find fertility factors conserved from C. elegans to mammals achieved its goal: of mouse gene knockouts corresponding to nematode proteins, 37% (7/19) cause male sterility. Our list therefore provides significant opportunity to identify causes of male infertility and targets for male contraceptives.

Sex chromosome silencing in the marsupial male germ line

“…Until recently, spermatozoa were believed to deliver little more than DNA into the oocyte. However, several studies now lend credence to paternal inheritance of both RNA and nonprotamine proteins that may be critical to early embryonic development (57)(58)(59)(60). Given the apparent absence of the XIC, could epigenetic programming initiated by MSCI and maintained by PMSC survive protamine packaging to establish imprinted XCI in the marsupial embryo?…”

Counting sperm does not add up any more: time for a new equation?

“…The comprehensive and systematic identification and quantification of proteins expressed in cells and tissues are providing important and fascinating insights into the dynamics of cell function (Chu et al 2006, Rifai et al 2006). Yet, although spermatozoa are ideal to study from a proteomic perspective, until very recently, there have ] i -signalling (blue line) 'switch' between minimum and maximum in minutes.…”

Regulation of Sperm-Specific Proteins by IFE-1, a Germline-Specific Homolog of eIF4E, in C. elegans

“…Comparative proteomic analysis between fem-3(q20) and ife-1(ok1978); fem-3(q20) worms Although it has been previously attempted (Chu et al, 2006), it is fairly difficult to obtain a large worm population consisting of 100% males because males cannot produce progeny by themselves. On the other hand, it is easy to obtain a large population of 100% hermaphrodite worms since they can produce progeny by self-fertilization and the produced progeny are all hermaphrodites.…”