The protein phosphatase with EF‐hand domain 1 is a calmodulin‐binding protein that interacts with proteins involved in sperm capacitation, binding to the zona pellucida, and motility

Abstract

Spermatozoa are highly specialized cells whose fertilizing and motility functions highly depend on intracellular Ca2+‐mediated events and protein posttranslational modifications like phosphorylation. Our group previously identified PPEF1, the Ser/Thr phosphatase with EF‐hand domain 1, among calmodulin‐affinity pulled down sperm proteins. As the mammalian ortholog of the Drosophila phosphatase rdgC that dephosphorylates rhodopsin, PPEF1 has been studied mostly in the retina. The presence and importance of this Ca2+/calmodulin‐binding protein phosphatase has not been studied in sperm or testicular functions despite its high expression level. In this study, we show that PPEF1 is present in testicular germ cells, and in mouse, human and bull spermatozoa where it is localized predominantly in the neck and acrosome areas. Different transcript variants encoding four predicted isoforms were detected by reverse transcription polymerase chain reaction in bull testis, spermatocytes and spermatids. Phosphatase activity of immunoprecipitated sperm PPEF1 was detected using the substrate pNPP and analysis of the coimmunoprecipitated proteins reveal an enrichment in the biological processes of sperm capacitation, binding to the zona pellucida and motility. Although this is the first demonstration of the presence of PPEF1 in sperm and testicular germ cells, its involvement in sperm fertilizing ability and motility, and the mechanisms regulating its activity remain to be further investigated.

STYXL1 regulates CCT complex assembly and flagellar tubulin folding in sperm formation

“…Further literature analysis of these ten phosphatases (PPM1B, STYXL1, PGP, EYA4, CDC14A, PPEF1, DUSP21, DUSP13, PP2D1, and HDHD1A) showed that (Fig. 1C ) three phosphatases, including PPM1B, PGP and EYA4, are essential to prevent embryonic lethality 33 – 35 ; deletion of Cdc14a causes spermatogenic defects 36 ; DUSP13 is involved in meiosis regulation; 37 PPEF1 is related to sperm fertilizing and motility 38 ; PP2D1 is dispensable for spermatogenesis 39 ; HDHD1A may be central in the epigenetic and genomic regulation of sex chromosome aneuploidies 40 . Only STYXL1 and DUSP21 have not been studied before in mouse, while STYXL1 is highly conserved from elegans to humans according to multiple sequence alignment analysis (Supplementary Fig.…”