Studies on the acrosome. 8. The intact starfish acrosome

Ultrastructural localization of acrosome reaction-inducing substance (ARIS) on sperm of the starfish Asterias amurensis

Using colloidal gold tagged ligands we have identified the ultrastructural site of ARIS binding to intact and acrosome-reacted starfish sperm. In intact sperm, colloidal gold conjugated ARIS was specifically localized to a single domain (0.1-0.3 micron in diameter) on the plasma membrane. This site was located on the anterior-lateral aspect of the sperm head, that is, just peripheral to the region occupied by the acrosomal vesicle and periacrosomal components. When sperm were labeled with colloidal gold conjugated ARIS, washed to remove unbound label, and then induced to undergo the acrosome reaction, the labeled patch remained associated with the plasma membrane and was positioned just lateral to the acrosomal process. However, when sperm were suspended in labeled ARIS and induced to undergo the acrosome reaction, label was observed along the entire anterior aspect of the sperm head with the exception of the acrosomal process. Labeling along the entire anterior aspect of the sperm head in this case was deemed to be nonspecific and due to binding of colloidal gold tagged molecules to components formerly located within the acrosomal vesicle, as the same pattern was obtained using colloidal gold tagged bovine serum albumin. Quantitative and qualitative aspects of ARIS binding observed here by electron microscopy are in agreement with measured binding characteristics previously reported (Ushiyama et al., 1993a: Zygote 1:121-127; Ushiyama et al., 1993b: J Reprod Dev 39:53-54), and indicate that the site of labeled ARIS binding represents a specific plasma membrane domain occupied by ARIS receptors.

Arylsulfatase of sea urchin sperm--distribution of arylsulfatase in the gonads and gametes of echinoderms

1. Fairly high activities of arylsulfatase are found in the sperm and mature testes of all the sea urchins studied; Strongylocentrotus intermedius, Strongylocentrotus nudus, Hemicentrotus pulcherrimus and Anthocidaris crassispina, whereas the activities in the ovaries and eggs of these animals are low. 2. Neither the sand dollar, Clypeaster japonicus nor the starfishes, Asterias amurensis and Asterina pectinifera prove to have considerable activities of the enzyme in their gonads and gametes. 3. Most of the activity of arylsulfatase in the sperm of S. intermedius is found in the seminal plasma, but the significant activity is bound to the spermatozoa. 4. Part, if not all, of the spermatozoa-borne arylsulfatase is suggested to exist on the surface of spermatozoa or in the acrosome or both. 5. The ubiquitous distribution of sperm arylsulfatase in sea urchins on the contrary to its absence in starfish or sand dollar is discussed in connection with the penetration of sperm through egg investments.

The polymerization of actin. II. How nonfilamentous actin becomes nonrandomly distributed in sperm: evidence for the association of this actin with membranes

At an early stage in spermiogenesis the acrosomal vacuole and other organelles including ribosomes are located at the basal end of the cell. From here actin must be transported to its future location at the anterior end of the cell. At no stage, in the accumulation of actin in the periacrosomal region is the actin sequested in a membrane-bounded compartment such as a vacuole or vesicle. Since filaments are not present in the periacrsomoal region during the accumulation of the actin even though the fixation of these cells is sufficiently good to distinguish actin filaments in thin section, the actin must accumulate in the nonfilamentous state.

The fine structure of the sperm of a holothurian and an ophiuroid

The fine structure of the mature sperm of the holothurian, Cucumaria miniata, and the ophiuroid, Ophiopholis aculeata, is described with particular reference to their acrosomal and centriolar satellite complexes, and compared to the sperm of other echinoderms. In Cucumaria, the acrosome is in the form of a diffuse acrosomal vesicle. It is unusual in that it apparently lacks an acrosomal membrane. A membrane separating the acrosomal vesicle from the periacrosomal material may not be equivalent to a typical inner acrosomal membrane. In Ophiopholis, the acrosome is dense, with some internal substructure, and is enclosed by a complete acrosomal membrane. In both species, the acrosome is partially surrounded by an amorphous periacrosomal mass. There is a notable absence of a subacrosomal depression and associated structures as found in other echinoderm sperm. The centriolar satellite complex (CSC) is essentially identical in both species. A reconstruction of the CSC is presented. The CSC consists of nine satellites radiating angularly from the distal centriole, each bifurcating at a dense node before inserting on a marginal ring containing circumferential microtubules. The ring is probably a cytoskeletal element. Immediately below the satellites are nine Y-shaped connectives, connecting each of the axonemal alpha doublets to the flagellar membrane.

The polymerization of actin: its role in the generation of the acrosomal process of certain echinoderm sperm

When Asterias or Thyone sperm come in contact with egg jelly, a long process which in Thyone measures up to 90 microm in length is formed from the acrosomal region. This process can be generated in less than 30 s. Within this process is a bundle of microfilaments. Water extracts prepared from acetone powders of Asterias sperm contain a protein which binds rabbit skeletal muscle myosin forming a complex whose viscosity is reduced by ATP. Within this extract is a protein with the same molecular weight as muscle actin. It can be purified either by collecting the pellet produced after the addition of Mg(++) or by reextracting an acetone powder of actomyosin prepared by the addition of highly purified muscle myosin to the extract. The sperm actin can be polymerized and by electron microscopy the polymer is indistinguishable from muscle F-actin. The sperm actin was shown to be localized in the microfilaments in the acrosomal processes by: (a) heavy meromyosin binding in situ, (b) sodium dodecyl sulfate (SDS) gel electrophoresis of the isolated acrosomal processes and a comparison to gels of flagella which contain no band corresponding to the molecular weight of actin, and (c) SDS gel electrophoresis of the extract from isolated acrosomal caps. Since the precursor for the microfilaments in the unreacted sperm appears amorphous, we suspected that the force for the generation of the acrosomal process is brought about by the polymerization of the sperm actin. This supposition was confirmed, for when unreacted sperm were lysed with the detergent Triton X-100 and the state of the actin in the sperm extract was analyzed by centrifugation, we determined that at least 80% of the actin in the unreacted sperm was in the monomeric state.