. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SPERMIOGENESIS AND FERTILIZATION IN A LIMPET 317 AV. -EP Figure 27. Diagram of mature sperni of Tectura /omi/m<//n. Note: site of actin in acrosomal tip (AI, acrosomal vesicle (AV). subacrosomal space (SS). posterior lobe (PL), flocculent material of subacrosomal space (F). nucleus (N), proximal centriole (PC), distal centriole and centriolar satellite connectives attached via annulus (An) to plasma membrane, mitochondrion (M). flagellum (Fl). and dense end-piece (EP) with reduced microtubules. One key difference between
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SPERMIOGENESIS AND FERTILIZATION IN A LIMPET 317 AV. -EP Figure 27. Diagram of mature sperni of Tectura /omi/m<//n. Note: site of actin in acrosomal tip (AI, acrosomal vesicle (AV). subacrosomal space (SS). posterior lobe (PL), flocculent material of subacrosomal space (F). nucleus (N), proximal centriole (PC), distal centriole and centriolar satellite connectives attached via annulus (An) to plasma membrane, mitochondrion (M). flagellum (Fl). and dense end-piece (EP) with reduced microtubules. One key difference between T. testiidimtlis and other molluscan groups is the nature of the acrosomal process that extrudes the inner acrosomal membrane. In some vetigastropods. flocculent material located in the subacro- somal space is responsible for everting the inner acroso- mal membrane by polymerization to a filamentous axial rod (Azevedo et ai, 1985). In other invertebrate species, including many echinoderms. arthropods, and annelids (see review by Dan, 1967), an acrosomal process is ex- truded from the subacrosomal space after polymerization of fibrogranulur material into a microfilamentous rod. This contrasts with the mechanism observed in other mol- luscs— including some archaeogastropods (Lewis et ai. 1980) and bivalves (Tilney, 1985: Tilney et ai, 1987)— in which intersliding of actin filaments arranged in pre- formed rods causes extension of the acrosomal process. Exactly how the inner acrosomal membrane everts in T. tesmdinalis is not known, but a similar polymerization of the flocculent fibrogranular material in the subacroso- mal space by an actin-based mechanism is likely, consid- ering that this site was one of three where actin was located in the related species. T. scutum. The final result is the extension of a short, broad acrosomal process, which contacts the egg microvilli and results in sperm-egg fu- sion. This type of acrosome reaction, as well as subse- quent sperm entry int
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
