Preferential attachment of cock spermatozoa to the perivitelline layer directly over the germinal disc of the hen's ovum.

In vitro incubation of cock spermatozoa with perivitelline layer (PL) from recently ovulated ova of the hen resulted in binding of spermatozoa to the PL and activation of the acrosome reaction. A simple quantitative technique was developed for assessing these events. Following incubation of the PL (0.5 cm2 sections) with spermatozoa, the PL section was rinsed and stained with Schiff's reagent. Microscopic examination revealed holes in the PL that were assumed to be sites of spermatozoa penetration. Utilizing this technique, a correlation was demonstrated between sperm concentration and the number of spermatozoa attaching to the PL and undergoing an acrosome reaction. Pre-treatment of spermatozoa with solubilized PL inhibited spermatozoa binding to pieces of intact PL. The PL overlying the germinal disc and a similarly sized section of PL from another area of the ovum were removed and incubated separately with spermatozoa (1 x 10(5) sperm/100 microliters). Spermatozoa showed preferential attachment and digestion of the PL from the germinal disc area (809 sperm/mm2) as compared to PL from other areas of the ovum (608 sperm/mm2). Spermatozoa attached to the PL in a circular, doughnut-shaped fashion in the area directly over the germinal disc.     

Zyxin controls migration in epithelial–mesenchymal transition by mediating actin‐membrane linkages at cell–cell junctions

Development is punctuated by morphogenetic rearrangements of epithelial tissues, including detachment of motile cells during epithelial–mesenchymal transition (EMT). Dramatic actin rearrangements occur as cell–cell junctions are dismantled and cells become independently motile during EMT. Characterizing dynamic actin rearrangements and identifying actin machinery driving these rearrangements is essential for understanding basic mechanisms of cell–cell junction remodeling. Using immunofluorescence and live cell imaging of scattering MDCK cells we examine dynamic actin rearrangement events during EMT and demonstrate that zyxin–VASP complexes mediate linkage of dynamic medial actin networks to adherens junction (AJ) membranes. A functional analysis of zyxin in EMT reveals its role in regulating disruption of actin membrane linkages at cell–cell junctions, altering cells' ability to fully detach and migrate independently during EMT. Expression of a constitutively active zyxin mutant results in persistent actin‐membrane linkages and cell migration without loss of cell–cell adhesion. We propose zyxin functions in morphogenetic rearrangements, maintaining collective migration by transducing individual cells' movements through AJs, thus preventing the dissociation of individual migratory cells. J. Cell. Physiol. 222: 612–624, 2010. © 2009 Wiley‐Liss, Inc.