Expression of full‐length and truncated Fyn tyrosine kinase transcripts and encoded proteins during spermatogenesis and localization during acrosome biogenesis and fertilization

Abstract

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.

The association between CDC42 and caveolin-1 is involved in the regulation of capacitation and acrosome reaction of guinea pig and mouse sperm

“…Several members of the SFK such as cYes, c-SSC, Fyn, and Lyn have been involved in sperm capacitation (Leclerc & Goupil 2002, Baker et al 2006, Kierszenbaum et al 2009, Goupil et al 2011. SU6656 has been identified as an inhibitor closely related to these kinases; in spite of this, our results do not clarify which kinase is related to CAV1 phosphorylation.…”

Cytoskeletal track selection during cargo transport in spermatids is relevant to male fertility

“…The coexistence of FerS, although at a low level, and FerT transcripts in pachytene spermatocyte suggests that the two forms of also supply membrane-associated GMAP210 as well as other proteins to the acrosome sac. Additional proteins include IFT88, testis-expressed FerT tyrosine kinase; 23 Fyn tyrosine kinase; 24 and members of the ubiquitin-proteasome system. 12 Whether these and other proteins utilize the acrosome membrane pathway to contribute to acrosome biogenesis and also as a strategy to reach a juxtanuclear niche position to participate in nuclear condensation and transcriptional inactivation need to be explored.…”

“…Full-length and truncated transcripts of Fyn tyrosine kinase are expressed during testicular development. 24 Truncated Fyn (designated tr-Fyn) transcripts encode a 24 kDa protein with a N-terminal domain, a complete Src homology (SH) 3 domain and an incomplete SH2 domain. The kinase domain is missing in tr-Fyn.…”

Role of FYN Kinase in Spermatogenesis: Defects Characteristic of Fyn-Null Sperm in Mice1

“…In the testis, both the SRC and the structurally similar YES kinases are associated with basal and apical ectoplasmic specializations (ES junctions) of Sertoli cells and are important for junctional dynamics [4][5][6]. FYN kinase is known to be expressed in two isoforms in the testis: a catalytically active 59-kDa form present in Sertoli cells and spermatozoa and a 22-kDa truncated form (tr-FYN) found in Sertoli cells and spermatids [7]. FYN also is associated with ES junctions in association with actin filaments bundled within these junctions, and structural analysis of the Fyn-null testis has revealed significant ultrastructural defects in apical ES junctions [8], suggesting that FYN may play a role in maintaining junction stability.…”

“…FYN also is associated with ES junctions in association with actin filaments bundled within these junctions, and structural analysis of the Fyn-null testis has revealed significant ultrastructural defects in apical ES junctions [8], suggesting that FYN may play a role in maintaining junction stability. In addition, expression and localization of tr-FYN in round and elongating spermatids led to the hypothesis that tr-FYN may function in sperm head morphogenesis and acrosomal development [7]. While the above-described functional roles of FYN are supported by circumstantial evidence, no functional evidence has confirmed either role.…”