Immunogold distribution of actin during sperimiogenesis in the normal rabbit and after experimental cryptorchidism

Abstract

Immunogold procedures for actin detection were used in combination with experimental cryptorchidism in the rabbit as a model to shed more light on the function of subacrosomal actin during spermiogenesis. In the normal testis, actin was localized in the perinuclear substance (PNS) from round spermatid onward but it was not detected in late spermatids. Actin labeling in each type of spermatid was essentially unmodified after 24 hr of cryptorchidism. However, among relevant immediate and delayed effects, discontinuous acrosomes overlying a continuous PNS with normal actin labeling were noted. Nuclear invaginations were seen in combination with subacrosomal dilatations; at this site actin labeling was found only in the PNS closely apposed to the nuclear envelope. In subacrosomal areas lacking PNS, actin labeling also was lacking. These results suggest that the subacrosomal actin (F-actin) is a component of the PNS that is tightly bound to the nuclear envelope rather than the overlying inner acrosomal membrane. Therefore, a function for the subacrosomal actin either in anchoring the acrosome to the nucleus or in capping the inner acrosomal membrane appears unlikely. The data rather suggest a capping function for the nuclear membrane during spermiogenesis.

Perinuclear theca during spermatozoa maturation leading to fertilization

“…This feature is observed in several mammalian spermatozoa types such as ground squirrel , rat (Russell et al, 1986;Fouquet et al, 1989a), boar (Camatini et al, 1986), hamster, monkey, human (Fouquet et al, 1989a(Fouquet et al, , 1990, and rabbit (Camatini et al, 1987;Fouquet et al, 1989b). In late spermatids there are both depolymerization of subacrosomal F-actin and a loss of actin immunolabeling, suggesting a dispersion of G-actin or G-actin relocation to other sperm regions, or protein masking (Fouquet et al, 1990).…”

Actin-Binding Properties and Colocalization with Actin During Spermiogenesis of Mammalian Sperm Calicin1

“…The role of F-actin and of its interaction with other perinuclear theca proteins is not known. Possible roles are anchorage of the acrosome [17,22,27,29] or shaping of the head by capping the nuclear membrane [26,30].…”

“…The subacrosomal layer of mammalian spermatids is also filled with actin, one of the ubiquitous cytoskeletal proteins, in its filamentous form (F-actin) during the greater part of spermiogenesis [20][21][22][23][24][25][26][27][28]. In late spermatids and spermatozoa of many species, most or all of the F-actin is depolymerized to G-actin and seems to be redistributed in a species-specific pattern [2,27,28].…”

The cytoskeleton of mammalian spermatozoa

“…In recent years normal spermatid morphogenesis was compared with pathological models: the experimentally cryptorchid rabbit [55] and mutant and transgenic mice [56][57][58]. These investigations have led to the following conclusions: 1) from round spermatid onwards, the polarity of the A variety of methods have demonstrated that the sperm plasma membrane is a mosaic of domains [5].…”