Functional diversity and evolution of the Drosophila sperm proteome

Abstract

Given the central role fertilization plays in the health and fitness of sexually reproducing organisms and the well-known evolutionary consequences of sexual selection and sperm competition, knowledge gained by a deeper understanding of sperm (and associated reproductive tissues) proteomes has proven critical to the field’s advancement. Due to their extraordinary complexity, proteome depth-of-coverage is dependent on advancements in technology and related bioinformatics, both of which have made significant advancements in the decade since the last Drosophila sperm proteome was published. Here we provide an updated version of the Drosophila melanogaster sperm proteome (DmSP3) using improved separation and detection methods and an updated genome annotation. We identified 2563 proteins, with label-free quantitation (LFQ) for 2125 proteins. Combined with previous versions of the sperm proteome, the DmSP3 contains a total of 3176 proteins. The top 20 most abundant proteins contained the structural elements α- and β-tubulins and sperm leucyl-aminopeptidases (S-Laps). Both gene content and protein abundance were significantly reduced on the X chromosome, a finding consistent with prior genomic studies of the X chromosome gene content and evolution. We identified 9 of the 16 Y-linked proteins, including known testis-specific male fertility factors. LFQ measured significant levels for 75/83 ribosomal proteins (RPs) we identified, including a number of core constituents. The role of this unique subset of RPs in sperm is unknown. Surprisingly, our expanded sperm proteome also identified 122 seminal fluid proteins (Sfps), proteins found predominantly in the accessory glands. The possibility of tissue contamination from seminal vesicle or other reproductive tissues was addressed using concentrated salt and detergent treatments. Salt treatment had little effect on sperm proteome composition suggesting only minor contamination during sperm isolation while a significant fraction of Sfps remained associated with sperm following detergent treatment suggesting Sfps may arise within, and have additional functions, in sperm per se.