Nuclear Fossa Research Articles

Membrane specializations associated with the acrosomal complex of sea urchin sperm as revealed by immunocytochemistry and freeze fracture replication.

Observations, employing freeze fracture replication and electron microscopic immunochemistry, have been carried out to determine structural correlations of the plasma membrane domain occupied by a 210 kDa protein involved in the acrosomal reaction of sea urchin sperm and recognized by the monoclonal antibody, J10/14 (Trimmer et al.: Cell 40:697-703, 1985; Proceedings of the National Academy of Sciences of the United States of America 83: 9055-9059, 1986). Immunogold-J10/14 staining of acrosome-intact sperm was intense along the flagellum and a narrow collar just posterior to the sperm apex that surrounded the acrosomal complex (acrosomal vesicle and subjacent anterior nuclear fossa containing g-actin). Counts of gold particles revealed a density (average number of particles/micron2 of surface area) eightfold greater along the plasma membrane associated with the acrosomal complex than membrane delimiting the remainder of the sperm head. The collar of J10/14 staining was isomorphic with a dense aggregation of intramembranous particles in the P-face of the plasma membrane and a thin cytoplasmic region that surrounded the acrosomal complex. In acrosome-reacted sperm, intense J10/14 staining was distributed along the flagellum and sperm head; prominent anterior staining was not apparent in all specimens. The density of gold particles associated with plasma membrane delimiting components of the former acrosomal complex, nucleus and mitochondrion, as well as the total average number of particles along the entire sperm surface, were increased in sperm acrosome-reacted with A-23187. Concomitant with this change in staining was the disappearance/reduction of the collars of intramembranous particles and cytoplasm. These observations indicate that plasma membrane components (210 kDa protein and intramembranous particles) and the collar of cytoplasm which are associated with the acrosomal complex are functionally, as well as structurally related. Analyses of particle density distributions along acrosome- and non-acrosome-reacted sperm suggest that the different staining patterns observed may be brought about by the recognition of cryptic sites at the time of the acrosomal reaction.

The phylogenetic position of the heteropodAtlanta gaudichaudiSouleyet (Mollusca, Gastropoda), a spermatological investigation

The male adult, the spermatophore and the spermatozoa ofAtlanta gaudichaudiare described. No parasperm are demonstrable. The ultrastructure of the spermatozoa is shown to differ fundamentally from that of the Archaeogastropoda and Neritopsina and to conform broadly with that of the Mesogastropoda (excepting Cyclophoracea, Viviparacea and Cerithacea), the Neogastropoda and the epitonacean heterogastropods. In having a nuclear fossa, containing the axoneme, which penetrates the entire length of the nucleus as the intranuclear canal, the spermatozoon especially resembles that of some members of the Rissoacea, Littorinacea, Eulimacea, Tonnacea, Volutacea and Conacea. Absence, inAtlantaof type 7 parasperm (sensuKoike 1985), which characterize the Calyptraeacea, Cypraeacea, Tonnacea, Buccinacea, Volutacea (including the Mitracea) and most Conacea, or of type 8 parasperm of the Conidae, contraindicates heteropod relationship with these taxa. Relationship to the Rissoacea cannot be ruled out, though presence of oligopyrene, cusperm‐like sperm in these (Bythiniidae) and pterotracheid heteropods is a questionable indication of affinity. Relationship of heteropods with the Littorinacea is suggested by similarity of the sperm, presence in carinariid heteropods and littorinids of nurse cells, and apparent homology of the male reproductive apparatus in both groups. The latter two similarities require confirmation, however. It is suggested that deposition of spermatophores on the exterior of the female in atlantid heteropods is a primitive mode of sperm transfer compatible with relationship with the Littorinacea.

Spermatozoal Ultrastructure in Branchiostoma moretonensis Kelly, a Comparison with B. lanceolatum (Cephalochordata) and with other Deuterostomes

The spermatozoon of Branchiostoma moretonensis closely resembles that of B. lanceolatum and, though near the primitive sperm, allows recognition of a cephalochordate sperm type. This has: a bell‐shaped acrosome; diffuse subacrosomal material not structured as an acrosome rod; sub‐ovoidal nucleus with shallow anterior concavity, deep tubular posterior fossa (endonuclear canal) and condensed but lacunate chromatin; single asymmetrical, postnuclear mitochondrion almost completely or completely encircling the centrioles; mutually perpendicular proximal and distal centrioles of the triplet type, with the distal forming the basal body of the flagellum and the proximal (always?), as in B. moretonensis, with a spur‐like extension (striated rootlet) into the nuclear fossa; flagellum tilted relative to the longitudinal axis (and endonuclear canal) of the nucleus; a 9 + 2 axoneme with hollow tubules and both dynein arms present on the doublets; and scattered glycogen granules, numerous around the distal centriole. The mitochondrion of B. moretonensis is C‐shaped in transverse section, as in urochordates, but cephalochordate sperm resemble those of echinoderms, and specifically holothuroids, more closely. The occurrence of flagellar rootlets and composite mitochondria in various animal groups is discussed. The term paramorphy is proposed for parallel and convergent acquisition of an identical character: symparamorphy where acquisition is by parallelism and alloparamorphy where it is by convergence; the two terms represent, however, extremes of a continuum. Superficially similar but structurally different characters acquired by convergence are termed analogomorphis.

Morphology of abalone spermatozoa before and after the acrosome reaction

Spermatozoa of the red abalone, Haliotis rufescens, consist of a bullet-shaped acrosome granule (2.5 × 1.1 μm), a nucleus (4.2 × 1.0 μm), a midpiece (0.75 × 1.3 μm) consisting of five mitochondria, a pair of centrioles and a series of vesicles, and a flagellum (45 × 0.25 μm). The large acrosome granule contains two distinct components: (1) an ovoid electron-dense body in the anterior apex of the granule (approximately 0.9 × 1.0 μm), and (2) a less dense, homogeneous material at the granule posterior. A bundle of preformed actin filaments (about 2.4 μm in length) protrude from the anteriorly located nuclear fossa into the acrosomal fossa located at the posterior of the acrosome granule. The acrosome reaction of Haliotis sperm can be triggered by 30 mM Ca2+ in the sea water, the ionophore A23187, or the aging of sperm. Upon reaction, the acrosome granule releases water-soluble components (thought to be the less electron-dense, posterior material of the granule, leaving a ghost-like empty sac with a wall approximately 0.03 μm in thickness. The extension of the actin-cored acrosome process occurs immediately after the exocytosis of the acrosome granule. The process (7 μm in length × 0.2 μm in width) extends through the sheath-like ghost of the acrosome granule. The inner surface of the ghost is studded with globules (about 0.04 μm diameter). The outer surface of the acrosome process is coated with dense material which may function in sperm-egg adhesion. Abalone sperm are of the “primitive” type of sperm morphology.

Spermiogenesis in the teleost Gambusia affinis with particular reference to the role played by microtubules.

During nuclear elongation in spermatids of Gambusia affinis, a deep fossa is formed at the base of the nucleus in which the centriolar complex and proximal portion of the flagellum reside. To stabilize the positional relationship between the nucleus and centriolar complex, while nuclear morphogenesis is taking place, a series of microtubules develop which emanate from the centriolar complex and extend to the nuclear envelope lining the fossa. Buttressing microtubules also develop within the nuclear fossa which both originate and insert along the nuclear envelope. These appear to stabilize nuclear shape prior to the time when chromatin condensation has proceeded to the stage where it could lend structural stability to nuclear form. Microtubules develop only after specific nuclear morphogenic events have taken place. It is therefore concluded that the spermatid nucleus is capable of "self-assembly" involving microtubules in a supportive role in addition to stabilizing the nuclear-flagellar relationship in G. affinis. The pattern of nuclear fossa-associated microtubules in G. affinis is significantly different from that observed in other poeciliid teleosts indicating a degree of species specificity with regard to both the timing of appearance and total number of microtubules.