Program of F-actin in the follicular epithelium during oogenesis of the german cockroach, Blattella germanica

Abstract

Extensive programmed structural and functional changes of insect follicular epithelium during oogenesis provide a model to study modulation of cytoskeletal organization during morphogenesis in a non-dividing cell population. Rhodamine-phalloidin staining of whole mounted and cryosectioned oogenic follicles reveal changing F-actin filament organization from pre- to post-vitellogenic stages consistent with the presumptive dorsal-ventral orientation of the future embryo. Filaments are not abundant in pre-vitellogenic follicle cells up to day 2. Differences between dorsal and ventral follicle cells appear first on day 3. Obviously patent follicle cells are seen only on the ventral follicle surface which exhibits stronger F-actin fluorescence than the dorsal non-patent epithelium. On the presumptive ventral side of midvitellogenic follicles morphologically distinct bundles of actin filaments orient peripherally into projections connecting adjacent follicle cells and from the center of follicle cells apically into macrovillar projections extending toward the oocyte surface. The mid-vitellogenic dorsal follicle cell layer also possesses macrovillar extensions containing F-actin which reach and appear to penetrate the oolema. During chorion deposition major reorganization of actin of follicle cells takes place. After chorion deposition all F-actin filaments within a given follicle cell are arranged into large parallel bundles with semi-regular cross-striations which exclude fluorescent label. The parallel orientation of actin striated filament bundles within each follicle cell appears to be random with respect to the orientation of bundles in neighboring follicle cells over much of the mid-latitude of the follicle epithelium. At anterior and posterior follicle poles a more axial orientation of striated bundles is evident. This muscle-like tissue arrangement is appropriate for cooperation in ovulating the chorionated oocyte from the follicle into the oviduct.