Abstract: In order to understand the dynamics of F-actin during spermiogenesis in Gampsocleis gratiosa Brunner von Wattenwyl, we demonstrated the cellular localization of F-actin during spermiogenesis using differential interference contrast microscopy and immunofluorescence microscopy, and observed the ultrastructure of the acrosomal complex using transmission electron microscopy. The results show that F-actin is detected in the subacrosomal space at the early spermatid stage, with shape from globular to rod-cone-like. At the middle spermatid stage, F-actin is detected in the subacrosomal space and two sides of the nuclear forepart, and looks like an inverted Y. At the late spermatid stage, F-actin looks like an arrow only in the extension wings of the acrosomal complex. F-actin was depolymerized and disappeared, only being located at subacrosomal region at the middle spermatid stage. The results suggest that the dynamics of F-actin is associated with the shape of spermatid nucleus and sperm head, and the acrosomal architecture and nuclear morphogenesis are supported by a dynamic F-actin skeleton during spermiogenesis. In addition, we discovered some cytoplasm droplets in the tail of immature sperm. Immunocytochemical and ultrastructural analysis indicated that these cytoplasm droplets contain abundant F-actin. The F-actin of cytoplasm droplets can be involved in expelling redundant cytoplasm and organelles during spermiogenesis. This study on the dynamics of F-actin provides the foundation to clarify the function and mechanism of cytoskeletal proteins during insect spermiogenesis.

Key words: Gampsocleis gratiosa, Factin, spermiogenesis, acrosomal complex, cytoplasm droplet, organelle