SLC6 family transporter SNF-10 is required for protease-mediated activation of sperm motility in C. elegans

Abstract

Summary Motility of sperm is crucial for their directed migration to the egg. The acquisition and modulation of motility are regulated to ensure that sperm move when and where needed, thereby promoting reproductive success. One specific example of this phenomenon occurs during differentiation of the amoeboid sperm of C. elegans as they activate from a round spermatid to a mature, crawling spermatozoon. Sperm activation is regulated by redundant pathways to occur at a specific time and place for each sex. Here, we report the identification of the solute carrier 6 (SLC6) transporter protein SNF-10 as a key regulator of C. elegans sperm activation in response to male protease activation signals. We find that SNF-10 is present in sperm and is required for activation by the male but not by the hermaphrodite. Loss of both snf-10 and a hermaphrodite activation factor render sperm completely insensitive to activation. Using in vitro assays, we find that snf-10 mutant sperm show a specific deficit in response to protease treatment but not to other activators. Prior to activation, SNF-10 is present in the plasma membrane, where it represents a strong candidate to receive signals that lead to subcellular morphogenesis. After activation, it shows polarized localization to the cell body region that is dependent on membrane fusions mediated by the dysferlin FER-1. Our discovery of snf-10 offers insight into the mechanisms differentially employed by the two sexes to accomplish the common goal of producing functional sperm, as well as how the physiology of nematode sperm may be regulated to control motility as it is in mammals.

A New Player in the Spermiogenesis Pathway of Caenorhabditis elegans

“…This conversion is induced by two semiautonomous pathways. One pathway is male specific and is signaled by the extracellular protease TRY-5, which is thought to interact with SNF-10 on the sperm to initiate activation (Smith and Stanfield 2011;Fenker et al 2014). The present study stems from a pathway operating in both males and hermaphrodites and involving the spe-8 group gene products in signal transduction.…”

“…While we are only beginning to learn the details of the TRY-5 activation pathway (Fenker et al 2014), the spe-8 group activation pathway has received much attention. This signal is transduced through SPE-8 (Muhlrad 2001;Muhlrad et al 2014), SPE-12 (Shakes and Ward 1989;Nance et al 1999), SPE-19 (Geldziler et al 2005), SPE-27 (Minniti et al 1996), and SPE-29 .…”

SNF-10 connects male-derived signals to the onset of sperm motility inC. elegans

“…The fertility of these double mutant males led us to reason that snf-10 would not be generally required for sperm activation, and when we tested this, we found that snf-10 mutant males and hermaphrodites were both fertile. 17 This is likely because loss of snf-10 causes a defect that can be circumvented by exposing sperm to hermaphrodite-derived activation signals, which trigger activation through the alternative spe-8 group pathway.…”

“…In our recent paper, we describe one such factor: snf-10 (sodium:: neurotransmitter symporter family). 17 snf-10 provides the first known link connecting the protease signal to changes in sperm cell motility, and is particularly interesting because it encodes a member of a well-conserved and well-studied family of proteins, the Solute Carrier 6 (SLC6) family. These proteins are sodium-dependent transporters best known for importing neurotransmitters, amino acids or osmolytes across the plasma membrane into cells, although they can have other roles.…”

Co-option of alternate sperm activation programs in the evolution of self-fertile nematodes

“…During ejaculation, large TRY-5 reserves are secreted into the seminal fluid, where they activate male spermatids. Although their direct target is unknown, one possibility is SNF-10, a membrane protein found in sperm 21 .…”