Distribution of filamentous actin in and around spermatids and in spermatozoa of Australian conilurine rodents

Abstract

The distribution of filamentous actin around the maturing sperm head and in spermatozoa of four species of Australian conilurine rodents was investigated at the light and electron microscopic levels. Similar results were obtained for all the species studied. Mechanically isolated spermatids had NBD-phallacidin-positive longitudinal bands of fluorescence over the dorsolateral surface and, in late spermatids, bands of bright fluorescence passed perpendicularly from the dorsal convex to ventral concave surface. TEM observations indicated that these regions corresponded to filaments of ectoplasmic specializations and granular filamentous material around the tubulobulbar complexes, respectively. In testicular and cauda spermatozoa NBD-phallacidin fluorescent material was present in the two ventral processes that extended from the upper concave surface of the sperm head; also fainter material occurred along the concave border and as a dorsocaudal spur. Its distribution was identical for testicular and cauda spermatozoa. TEM of late spermatids showed that in the ventral process closest to the apical hook there were between 170 and 245 filaments, which attached to the inner surface of the postacrosomal dense lamina; in the more caudal ventral process about 70 filaments occurred. No filaments were, however, visible in the mature spermatozoon but, after immunocytochemical labelling for actin, deposition of gold particles was evident over ventral processes of both late spermatids and cauda spermatozoa. Within the female tract these ventral processes made contact with the zona matrix and were taken into the egg cytoplasm unchanged in morphology. The possible functional significance of the filamentous actin in these structures is discussed.

Immunocytochemical detection of actin and 53 kDa polypeptide in the epididymal spermatozoa of rat and mouse

“…So far, only nonfilamentous actin has been detected in the neck of mammalian sperm, including rat and mouse (Flaherty et al, 1983(Flaherty et al, , 1986(Flaherty et al, , 1988Virtanen et al, 1984;Welch and O'Rand, 1985;Breed and Leigh, 1991;Yagi and Paranko, 1992;Vogl et al, 1993). The present immunogold labeling results confirm the earlier reports localizing actin into the amorphous material on the neck region of human, bovine, and hamster spermatozoa (Flaherty et al, 1988).…”

“…Solubility of tail actin in SDS is supportive for its unpolymerized nature and agrees with the negative results obtained with fluorescent phallotoxins (Flaherty et al, 1983(Flaherty et al, , 1986Virtanen et al, 1984;Welch and O'Rand, 1985;Breed and Leigh, 1991;Yagi and Paranko, 1992;Vogl et al, 1993). Due to the crossreactivity of N350 antibody in the rat and mouse sperm tail and because of the different properties of solubility, the putative mutual associations between actin and 53 kDa polypeptide remained undetermined.…”

“…Later on, actin filaments seem to depolymerize and become undetectable by fluorescent phalloidiniphallacidin probes (Virtanen et al, 1984;Camatini et al, 1986;Flaherty et al, 1986;Fouquet et al, 1990;Yagi and Paranko, 1992). Recently, however, Vogl et al (1993) reported the presence of filamentous actin in the head of the rat sperm which, in turn, supports the earlier findings done in the Plains mouse (Flaherty et al, 1983) and Australian conilurine rodents (Breed and Leigh, 1991).…”

The spermatozoon of Eurasian murine rodents: Its morphological diversity and evolution

“…Transmission electron microscopy (TEM) of the sperm head of laboratory rats (Rattus norvegicus) and mice (Mus musculus) has since shown that this sperm head morphotype has a highly complex structural organization, with the apical hook containing a nuclear extension, extensive development of the subacrosomal space rostrally as a perforatorium, and a complex asymmetrical acrosome (Piko, 1969;Lalli and Clermont, 1981;Oko and Clermont, 1988). A further morphological elaboration of the sperm head occurs in most species of Australian hydromyine rodents where two additional extensions, largely made up of cytoskeletal material, project from the upper concave surface (Breed, 1984(Breed, , 1997Flaherty and Breed, 1983;Breed and Leigh, 1991;.…”

Protein Composition of the Ventral Processes on the Sperm Head of Australian Hydromyine Rodents1

“…These processes develop late in spermiogenesis and are largely composed of electron-dense material that is continuous with the perforatorium in the apical hook [15][16][17][18][19][20]. The chemical composition of these processes is largely unknown although filamentous actin has been shown to be present [17,18,[20][21][22] that is not present in the perforatorium of the mature sperm head of the laboratory rat [9,23,24]. The objective of the present study was to isolate the ventral processes (VPs) and determine their protein composition by SDS-PAGE and Western blotting, and by TEM after immunogold labeling with the use of antisera raised against proteins of the perforatorium in the laboratory rat and of the perinuclear theca in the bull.…”