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

Abstract

FYN kinase is highly expressed in the testis and has been implicated in testis and sperm function, yet specific roles for this kinase in testis somatic and germ cells have not been defined. The purpose of the present investigation was to identify aspects of spermatogenesis, spermiation, or sperm fertilizing capacity that required FYN for normal reproductive function. Matings between Fyn-null males and wild-type females resulted in normal litter sizes, despite the fact that Fyn-null males exhibited reduced epididymal size and sperm count. Morphological analysis revealed a high frequency of abnormal sperm morphology among Fyn-null sperm, and artificial insemination competition studies demonstrated that Fyn-null sperm possessed reduced fertilizing capacity. Fyn-null sperm exhibited nearly normal motility during capacitation in vitro but reduced ability to undergo the acrosome reaction and fertilize oocytes. The typical pattern of capacitation-induced protein tyrosine phosphorylation was slightly modified in Fyn-null sperm, with reduced abundance of several minor phosphoproteins. These findings are consistent with a model in which FYN kinase plays an important role in proper shaping of the head and acrosome within the testis and possibly an additional role in the sperm acrosome reaction, events required for development of full fertilizing capacity in sperm.

Src Kinase Is the Connecting Player between Protein Kinase A (PKA) Activation and Hyperpolarization through SLO3 Potassium Channel Regulation in Mouse Sperm

“…The use of a secondary antibody that specifically detects native IgGs avoided detection of denatured IgGs used for immunoprecipitation (see "Experimental Procedures"). Regarding the presence of other SFK members in mouse sperm, Fyn has been reported recently (21) to have an active role in spermatogenesis. To analyze the possible activation of Fyn during capacitation, the anti Tyr-416-Src was used because it cross-reacts with all members of the SFK family when phosphorylated at the analogous site (Tyr-420-Fyn).…”

“…Work from several laboratories has shown the presence of members of the Src family of kinases (SFK), in mouse sperm: cSrc (3,11,12) Fyn (13), and immunocytochemistry-based evidence on Lyn and Hck (11). However, recent work from our group using a combination of pharmacological and genetic approaches has shown that, although SFK inhibitors affect phosphorylation by up-regulation of Ser/Thr phosphatases, SFKs are not directly involved in the increase in tyrosine phosphorylation observed during sperm capacitation that follows PKA activation.…”

Role of Posttranslational Protein Modifications in Epididymal Sperm Maturation and Extracellular Quality Control

“…The phosphorylation of proteins is mediated by the activity of kinases that are present in spermatozoa including those of the MAP kinase pathway [ 15 -17 ], CaMKII alpha [ 18 ], FYN kinase [ 19 ], JAK/STAT [ 20 ] and many others. Most of these kinases have been studied from the standpoint of their roles in sperm capacitation and fertilization, and will not be addressed here.…”

The tyrosine kinase FER is responsible for the capacitation-associated increase in tyrosine phosphorylation in murine sperm

“…A list of potential candidate kinases has emerged based on pharmacological and immunological evidence. Among these candidates, the most relevant were SRC (Baker et al, 2006;Krapf et al, 2010;Varano et al, 2008), FYN (Luo et al, 2012), ABL (Baker et al, 2009), and both members of the focal adhesion kinase (FAK) family, FAK and proline-rich tyrosine kinase 2 (PYK2; also known as PTK2B) (Battistone et al, 2014;Gonzalez-Fernandez et al, 2013). All these enzymes were shown to be present in sperm and, furthermore, the increase in tyrosine phosphorylation was reduced or completely obliterated when treated with inhibitors against their respective activities.…”