Expression of full-length and truncated Fyn tyrosine kinase transcripts and encoded proteins during spermatogenesis and localization during acrosome biogenesis and fertilization.
We report that full-length and truncated transcripts of Fyn tyrosine protein kinase are expressed during testicular development. Truncated Fyn (tr-Fyn) transcripts encode a 24 kDa protein with a N-terminal (NT) domain, a complete Src homology (SH) 3 domain and an incomplete SH2 domain. The kinase domain is missing in tr-Fyn. In contrast, full-length Fyn transcripts encode a 59-55 kDa protein. Fractionated spermatids by centrifugal elutriation express tr-Fyn transcripts and protein, but not full-length Fyn transcripts and protein. Neither full-length Fyn nor tr-Fyn transcripts and encoded proteins are detected in elutriated pachytene spermatocytes. Sertoli cells express full-length and truncated Fyn throughout testicular development. In contrast, sperm contain full-length Fyn transcripts and protein but not the truncated form. tr-Fyn protein is visualized at the cytosolic side of Golgi membranes, derived proacrosomal vesicles, along the outer acrosome membrane and the inner acrosome membrane-acroplaxome complex anchoring the acrosome to the spermatid nuclear envelope. Fyn and phosphotyrosine immunoreactivity coexist in the tail of capacitated sperm. During fertilization, the Fyn-containing acroplaxome seen in the egg-bound and egg-fused sperm is no longer detected upon decondensation of the sperm nucleus. tr-Fyn expands the catalog of truncated tyrosine protein kinases expressed during spermiogenesis. We suggest that the NT and SH3 domains of tr-Fyn may recruit adaptor and effector proteins, in particular GTPase activating proteins, required for acrosome-acroplaxome biogenesis, acroplaxome F-actin dynamics and Sertoli cell function. During fertilization, full-length Fyn in the acroplaxome may contribute to a transient local signaling burst during the early events of sperm-egg interaction.
Kierszenbaum
Abraham L
AL
Department of Cell Biology and Anatomy, The Sophie Davis School of Biomedical Education/The City University of New York Medical School, New York, New York 10031, USA. kier@med.cuny.edu
Rivkin
Eugene
E
Talmor-Cohen
Anat
A
Shalgi
Ruth
R
Tres
Laura L
LL
D000177:Acrosome / Q000378:metabolism*; D000818:Animals; D005306:Fertilization / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D051076:Proto-Oncogene Proteins c-fyn / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012708:Sertoli Cells / Q000378:metabolism; D013075:Sperm Capacitation; D013087:Spermatids / Q000378:metabolism; D013091:Spermatogenesis / Q000502:physiology*; D013094:Spermatozoa / Q000378:metabolism; D013737:Testis / Q000378:metabolism
C494961:Fyn protein, rat; D051076:Proto-Oncogene Proteins c-fyn