Figure 3. Spatiotemporal expression of c-Yes, p-FAK-Tyr³⁹⁷ and p-FAK-Tyr⁴⁰⁷ at the apical ES at stage VI-VIII of the epithelial cycle in adult rat testes.

(A) At the apical ES, c-Yes (green fluorescence) is localized to the convex side of the spermatid head towards the tip of the head (“white” arrow) but also towards the back of the head (“red” arrow) in stage VI. In early VII, c-Yes is also detected at the concave side of spermatid heads (“yellow” arrow) which persists until late stage VII and no longer detected in stage VIII of the cycle. Expression of c-Yes at the convex side of spermatid heads is also considerably diminished in early VIII and almost non-detectable by late VIII. (B) p-FAK-Tyr⁴⁰⁷ (red fluorescence), an ES regulator, is expressed mostly at the concave side of spermatid heads, but the silencing of c-Yes by RNAi induces mis-localization of p-FAK-Tyr⁴⁰⁷, in which it diffuses away from the site. (C) Differential localization of p-FAK-Tyr³⁹⁷ and p-FAK-Tyr⁴⁰⁷ at the apical ES. p-FAK-Tyr³⁹⁷ is mostly expressed at the convex side of spermatid heads (“white” arrow) and persists through late stage VIII (but considerably diminished), whereas, p-FAK-Tyr407 is restricted mostly to the concave side of spermatid heads (“yellow” arrow) and diminishes considerably by late VIII. When these findings are compared to Figure 2, it is likely that Arp3, Eps8 and palladin are regulated by these non-receptor protein tyrosine kinases. For instance, p-FAK-Tyr⁴⁰⁷, which is expressed predominantly at the concave side of spermatid heads, likely regulates Arp3 and Eps8 (both are found at the concave side of spermatids heads, see Fig. 2). Whereas p-FAK-Tyr³⁹⁷ and c-Yes, which are predominantly expressed at the convex side of spermatid heads, regulate Eps8 and palladin (both are also found at the convex side of spermatid heads, see Fig. 2) by activating the corresponding actin regulatory protein(s) to effectively confer actin microfilaments either in a “bundled” to “unbundled/branched” configuration so that actin filaments at the ES can be effectively transformed and re-organized during the epithelial cycle to facilitate spermatid transport. Scale bar, 12 μm, which applies to other micrographs in the same panel.