UC Riverside

Sperm from a semi-aquatic insect, the water strider Aquarius remigis, are unusually long and possess a complex acrosome and flagellum. Like other animal systems, water strider sperm that emerge from the testis are incapable of fertilizing an egg and must undergo several highly regulated developmental steps in both the male and female reproductive tracts. However, in contrast to well-studied model animals such as mammals and echinoderms, little is known about these events in insects. In this dissertation, I describe the post-meiotic events in Aquarius remigis using biochemical and biophysical methodologies to follow the assembly, structure, and fate of the acrosome and the flagellum from spermatogenesis through fertilization and into early embryonic development. In contrast to other long insect sperm, half of the length of the A. remigis sperm consists of an acrosomal matrix that emerges as a 300 µm helical structure followed by a 2200 µm linear region. This unusually long acrosome contains an intrinsically fluorescent molecule with properties consistent with those of Flavin Adenine Dinucleotide (FAD). Biophysical analyses showed that FAD is immobilized and oriented during acrosome formation and may be involved in the formation of disulfide bond formation during its assembly. Further, using the intrinsic fluorescence as a marker, I followed the fate of the acrosomal matrix through fertilization and observed it inside the fertilized egg where it remained structurally intact through gastrulation. The acrosomal matrix may play roles in sperm transport and fertilization. Similar to the proximal acrosomal process, the axoneme and its associated structures, appears helical. I describe a unique motility pattern in which the flagellum loops back upon itself and forms a coil. This structure can then twist and undergo forward progressive motility with the loop acting as the anterior end. A. remigis sperm are quiescent in the seminal vesicles, but sperm motility was initiated by specific proteases or phosphatase inhibitors. Further, a broad spectrum kinase inhibitor blocked sperm motility initiation by trypsin. These results suggest that quiescence is maintained by high levels of endogenous phosphatase activity and that activation of motility is regulated by protein phosphorylation through the action of one or more kinases.