title: New insights into FAK function and regulation during spermatogenesis.
abstract: Germ cell transport across the seminiferous epithelium during the epithelial cycle is crucial to spermatogenesis, although molecular mechanism(s) that regulate these events remain unknown. Studies have shown that spatiotemporal expression of crucial regulatory proteins during the epithelial cycle represents an efficient and physiologically important mechanism to regulate spermatogenesis without involving de novo synthesis of proteins and/or expression of genes. Herein, we critically review the role of focal adhesion kinase (FAK) in coordinating the transport of spermatids and preleptotene spermatocytes across the epithelium and the BTB, respectively, along the apical ectoplasmic specialization (ES) - blood-testis barrier - basement membrane (BM) functional axis during spermatogenesis. In the testis, p-FAK-Tyr&#179;&#8312;&#8311; and p-FAK-Tyr&#8308;&#8304;&#8311; are spatiotemporally expressed during the epithelial cycle at the actin-rich anchoring junction known as ES, regulating cell adhesion at the Sertoli-spermatid (apical ES) and Sertoli cell-cell (basal ES) interface. Phosphorylated forms of FAK exert their effects by regulating the homeostasis of F-actin at the ES, mediated via their effects on actin polymerization so that microfilaments are efficiently re-organized, such as from their "bundled" to "de-bundled/branched" configuration and vice versa during the epithelial cycle to facilitate the transport of: (i) spermatids across the epithelium, and (ii) preleptotene spermatocytes across the BTB. In summary, p-FAK-Tyr&#8308;&#8304;&#8311; and p-FAK-Tyr&#179;&#8312;&#8311; are important regulators of spermatogenesis which serve as molecular switches that turn "on" and "off" adhesion function at the apical ES and the basal ES/BTB, mediated via their spatiotemporal expression during the epithelial cycle. A hypothetical model depicting the role of these two molecular switches is also proposed.
authors.affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA.
authors.forename: N Ece
authors.initials: NE
authors.lastname: Gungor-Ordueri
authors.affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA.
authors.forename: Dolores D
authors.initials: DD
authors.lastname: Mruk
authors.affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA.
authors.forename: Hin-ting
authors.initials: HT
authors.lastname: Wan
authors.affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA.
authors.forename: Elissa W P
authors.initials: EW
authors.lastname: Wong
authors.affiliation: Department of Histology and Embryology, Faculty of Medicine, Akdeniz University, Antalya, Turkey.
authors.forename: Ciler
authors.initials: C
authors.lastname: Celik-Ozenci
authors.affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA.
authors.forename: Pearl P Y
authors.initials: PP
authors.lastname: Lie
authors.affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA. Y-Cheng@popcbr.rockefeller.edu OR ccheng@rockefeller.edu.
authors.forename: C Yan
authors.initials: CY
authors.lastname: Cheng
mesh_terms: D000818:Animals; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D006801:Humans; D008297:Male; D013091:Spermatogenesis / Q000502:physiology*
chemical_list: D051416:Focal Adhesion Protein-Tyrosine Kinases