Nuclear morphogenesis during spermiogenesis in the nudibranch molluscHypselodoris tricolor (Gastropoda, opisthobranchia)

Abstract

An electron microscope study was carried out on Hypselodoris tricolor spermatids to describe the development of the nuclear morphogenesis and investigate the possible cause(s) of the change in the shape of the spermatid nucleus during spermiogenesis. Three different stages may be distinguished in the course of the nuclear morphogenesis on the basis of the morphology and inner organization of the nucleus. Stage I spermatid nuclei are spherical or ovoid in shape and the nucleoplasm finely granular in appearance. Stage 2 nuclei exhibit a disc-or cup-shaped morphology, and the chromatin forms short, thin filaments. During stage 3, a progressive nuclear elongation takes place, accompanied by chromatin rearrangement, first into fibers and then into lamellae, both formations helically oriented. A row of microtubules attached to the nuclear envelope completely surrounds the nucleus. Interestingly, the microtubules always lie parallel to the chromatin fibers adjacent to them. Late stage 3 spermatids show the highest degree of chromatin condensation and lack the manchette at the end of spermiogenesis. Our findings indicate the existence of a clear influence exerted on the chromatin by the manchette microtubules, which appear to be involved in determining the specific pattern of Chromatin condensation in Hypselodoris tricolor.

The ultrastructure of spermatozoa and spermiogenesis in pyramidellid gastropods, and its systematic importance

“…The pattern of spermiogenesis described here for the Pyramidellidae does not deviate from that occurring in other euthyneuran species (Opisthobranchia: Eckelbarger & Eyster, 1981;Kubo & Ishikawa, 1981;Medina et al, 1985Medina et al, , 1986; see also Thompson, 1973 for micrographs of late spermatid midpiece in ,the pyramidellid Odostomia sp.…”

Sperm tail differentiation in the nudibranch mollusc Hypselodoris tricolor (gastropoda, opisthobranchia)

“…During the spring and summer (April-August, 1984), adult specimens of the dorid nudibranch Hypselodoris tricolor were collected from the Straits of Gibraltar (Cadiz, Spain) at a depth of 15-20 m. For the ultrastructural study of differentiating male cells, small fragments of gonad were prepared for electron microscopy as described previously (Medina et al, 1986). Thin sections were mounted on copper grids and examined by Siemens Elmiskop electron microscope.…”

Comparison and cost benefit analysis of different data sets used for determining mollusc evolution: a case study of the cryptobranch nudibranch Halgerda (Mollusca: Gastropoda)

“…There have been a number of transmission electron microscopical (TEM) studies dealing with sperm or spermiogenesis of nudibranchs (Thompson 1966;Schmekel 1971;Holman 1972;Thompson 1973;Eckelbarger and Eyster 1981;Eckelbarger 1982;Medina et al 1985 and1986;Healy and Willan 1991;Wilson and Healy 2002). The majority of these authors either limited their study to a single group of Nudibranch (Thompson 1966 and1973;Holman 1972;Eckelbarger and Eyster 1981;Medina et al 1985 and1986) and/ or confined their study to a single structure within the sperm (Schmekel1971).…”

“…The majority of these authors either limited their study to a single group of Nudibranch (Thompson 1966 and1973;Holman 1972;Eckelbarger and Eyster 1981;Medina et al 1985 and1986) and/ or confined their study to a single structure within the sperm (Schmekel1971). No previous phylogeny has examined sperm ultrastructure across a genus of nudibranch.…”