USP8/UBPy-regulated sorting and the development of sperm acrosome: the recruitment of MET.
The acrosome is a peculiar vacuole that at fertilization undergoes the acrosome reaction (AR), an event unique in the sperm life. Contents released promote sperm penetration through oocyte's investments; membranous components are involved in sperm-egg interaction/fusion. Therefore, both constituents play a role in fertilization. The biogenesis of this vacuole, however, has not been clarified yet; recently, it has been proposed as a novel lysosome-related organelle (LRO). Our research focuses on the involvement of the endosomal pathway in acrosomogenesis starting from the early phases. The trafficking sorted by USP8/UBPy, an endosomal regulator recently described as a compelling candidate for male fertility gene, was investigated in comparison to that of SP56, a marker of the biosynthetic pathway. Mouse spermatids were double/triple immunolabeled and examined by confocal microscopy. The contribution of the vesicular traffic assisted by the cortical microtubule array was also evaluated in nocodazole-treated spermatids. USP8/UBPy-sorted cargo contributes early to acrosomogenesis and its trafficking is microtubule mediated. It was identified, through co-immunoprecipitation/co-immunolocalization assays, that the membrane receptor MET, described herein for the first time in spermatids, as an USP8/UBPy-target substrate is delivered to the acrosome. MET and USP8/UBPy still colocalize in epididymal spermatozoa. Following the AR, MET and USP8/UBPy show a distinct fate. MET, in particular, translocates at the PAS, the post acrosomal segment known to harbor sperm-borne factors involved in oocyte activation. Overall, our results support the concept of the acrosome as a LRO and provide evidence for the identification of MET as a tyrosine kinase receptor that may play a role in fertilization.
Department of BiosciencesUniversity of Milan, via Celoria 26, 20133 Milan, Italy giovanna.berruti@unimi.it.
Giovanna
G
Berruti
Department of BiosciencesUniversity of Milan, via Celoria 26, 20133 Milan, Italy.
Chiara
C
Paiardi
D000177:Acrosome / Q000187:drug effects / Q000378:metabolism*; D020101:Acrosome Reaction / Q000187:drug effects / Q000502:physiology; D000818:Animals; D010450:Endopeptidases / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism*; D008297:Male; D051379:Mice; D015739:Nocodazole / Q000494:pharmacology; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism*; D013076:Sperm Count; D013084:Sperm-Ovum Interactions / Q000502:physiology; D013087:Spermatids / Q000187:drug effects / Q000378:metabolism*; D013091:Spermatogenesis / Q000187:drug effects / Q000502:physiology; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism; D043222:Ubiquitin Thiolesterase / Q000378:metabolism*
D056827:Endosomal Sorting Complexes Required for Transport; D019859:Proto-Oncogene Proteins c-met; D010450:Endopeptidases; D043222:Ubiquitin Thiolesterase; C541536:Usp8 protein, mouse; D015739:Nocodazole