Arkadiy A. Reunov

Nuage constituents arising from mitochondria: is it possible?

An ultrastructural study of nuage–mitochondria complexes in spermatogonia of the sea urchin, Anthocidaris crassispina, was carried out. Release of mitochondrial contents into the cytoplasm was observed. The mitochondrial derivatives persisted as cristae‐containing globules of friable material that subsequently contacted and integrated with nuage. The present ultrastructural findings agree with the results of other researchers who proposed that germ plasm substance probably produced by the nucleus is supplemented by the mitochondrial genome.

Sublethal effects of phenol on spermatogenesis in sea urchins (Anthocidaris crassispina)

Adult sea urchins, Anthocidaris crassispina, were exposed to 0.1 and 10 mgL(-1) phenol for 4 weeks. Abnormal sperm development was clearly evident in phenol-treated sea urchins, although no mortality was found throughout the exposure period. Occurrences of multinucleate sperm cells (including spermatocytes to spermatozoa) showed a significant increase from 0.07% in the control to 10.7% and 43.3% in the 0.1- and 10-mgL(-1) treatments, respectively (P<0.01). Likewise, sperm with electron dense, dark tails increased significantly from 8% in the control to 36.6% and 43.4% in the 0.1- and 10-mgL(-1) phenol-treated sea urchins, respectively (P<0.01). In addition, disruption of cytoplasmic membranous structures such as loss of mitochondrial cristae and distortion of mitochondrial membranes and nucleus envelope were commonly found in phenol-treated spermatogonia and spermatocytes. Previous studies have clearly demonstrated motility impairment and a concomitant reduction of fertilization capability in sea urchin sperm with dark tails and/or distorted mitochondria. Our current findings therefore suggest that chronic exposure to phenol at 0.1 mgL(-1) could lower the quality of sperm and reproductive success in sea urchins, which may threaten the survival of these ecologically important species. The observed impairment of spermatogenesis by phenol might also occur in other invertebrate species.

Four lines of spermatid development and dimorphic spermatozoa in the sea urchin Anthocidaris crassispina (Echinodermata, Echinoida)

Abstract The process of sperm development in the sea urchin Anthocidaris crassispina was studied by light and electron microscopy. Similar to other echinoids studied, a single flagellum, striated rootlet and nuage-like materials were present in spermatogonia of A. crassispina. Spermatocytes near the diplotene stage showed intracellular localization of the axoneme which appeared to be a retracted flagellum prior to cell division. Fibrous filaments were associated with a proximal centriole in spermatocytes and spermatids and might be involved in movement of the proximal centriole. An acrosomal vesicle was developed and a residual body was formed in spermatids. The special development patterns in A. crassispina attributed to the presence of two patterns of tail development and two patterns of mitochondrial development during spermiogenesis. These four lines of spermiogenesis resulted in the formation of four morphological types of sperm cell, i.e. sperms with: (1) a symmetrical midpiece and posterior tail, (2) an asymmetrical midpiece and posterior tail, (3) a symmetrical midpiece and bent tail and (4) an asymmetrical midpiece and bent tail. Sperm cells with bent tails (type 3+4) were probably still at the late spermatid stage because results of scanning electron microscopy demonstrated gradual detachment and eventual straightening of the bent tail, and their percentage occurrence in the sperm population decreased significantly (P<0.05) towards the spawning season of A. crassispina. Spermatozoa with a symmetrical midpiece were dominant (averaging 70% occurrence in the sperm population) over those with an asymmetrical midpiece. The dimorphic spermatozoa in A. crassispina (types 1, 2) are both considered to be euspermatozoa as their morphology is typical for Echinoida.

Effects of selenium on growth and ultrastructure of the marine unicellular alga Dunaliella salina (Chlorophyta)

This study examines the effects of selenium in concentrations of 0.01, 0.5, 1, 5, and 10 mg/liter on the growth and ultrastructure of the microalga Dunaliella salina. Selenium in concentrations of 0.01 and 0.5 mg/liter stimulated cell population growth, while the number of ultrastructural alterations was the same as in the control cells. At a selenium concentrations of 1 mg/liter, cell population growth slightly decreased by the end of the experiment, and there was some increase in the number of cells with damaged organoids and in the number of completely destroyed cells. As well, the excretory function of cell vacuoles was suppressed, and the autophagic activity of these vacuoles was activated to destroy the cytoplasm and nucleus. Concentrations of 5 and 10 mg/liter were toxic to D. salina, suppressing cell population growth and promoting extensive destructive changes. The threshold concentration of selenium for D. salina was 1 mg/liter, which is 1000 times greater than the maximum permissible concentration (MPC). The fact that the microalga was able to survive for several days in this concentration is indicative of its high resistance to selenium.

An ultrastructural study of phagocytosis and shrinkage in nutritive phagocytes of the sea urchin Anthocidaris crassispina

The ultrastructural mechanisms of waste-sperm phagocytosis and postspawning shrinkage were studied for accessory cells (nutritive phagocytes; NPs) of the sea urchin Anthocidaris crassispina. Sperm cells were phagocytosed by NPs; they penetrated into the cytoplasm of the NPs inside heterophagosomes formed by an invagination of the cell membrane. Single-sperm-containing heterophagosomes aggregated to form large multisperm heterophagosomes that were accompanied by cytoplasmic vesicles and lipids. Two types of vesicle, viz., Golgi-complex-derived electron-dense vesicles (“zymogen granules”) and smooth-endoplasmic-reticulum-derived electron-lucent vesicles, were incorporated within multisperm heterophagosomes. Completed multisperm heterophagosomes were transformed into electron-dense remnant bodies, the content of which underwent destruction, resulting in “empty” vacuoles inside the remnant body. The “empty” vacuoles were then compressed by the surrounding cytoplasm. Shrinkage of NPs occurred upon completion of sperm degeneration in gonad tubules. This process was undertaken by structures termed cell-size-reducing autolysosomes, which performed two types of autolysis, and resulted in the formation of “cheese-hole”-like vacuoles in the cytoplasm of NPs. Subsequent cytoplasmic compression of these vacuoles was required for the reduction in size of NPs, an essential event for remodeling the cell for the next gametogenetic cycle.

Spermatogenesis of the green-lipped mussel Perna viridis with dual patterns of acrosome and tail development in spermatids

Abstract Spermatogenesis in the mussel Perna viridis was studied by electron microscopy. Results demonstrated that cytological development in spermatogonia and spermatocytes was similar to that previously described in other Mytilidae. Acrosome formation began with the arising of proacrosomal vesicles in spermatogonia. The abundance of proacrosomal vesicles increased in spermatocytes, which were flagellated. However, during spermiogenesis, dual patterns of acrosome development as well as flagellum development could be found among spermatids in a male gonad. The two lines of acrosome formation in spermatids ultimately gave rise to morphologically similar acrosomes. The two lines of flagellum development in spermatids resulted in the formation of sperm cells with either a typically posteriorly directed tail or an anteriorly directed tail.

Ultrastructure of hull formation during oogenesis in Rhyssoplax tulipa (=Chiton tulipa) (Chitonidae: Chitoninae)

Abstract Egg hull formation is described in detail for the first time in Rhyssoplax tulipa from South Africa. Although previous descriptions of hull formation in chitons provide some basis for comparison, the mechanisms we have discovered are totally different. The process begins with the release of clear vacuoles from the oocyte into the intercellular space, which separates it from a layer of follicle cells. Materials contributing to the layers of the hull are formed primarily by micro-apocrine secretion processes, in which extensions of the follicle cells and oocyte are budded off into the intercellular space, rather than by formation and release of vesicles from the Golgi bodies, as previously thought. Later in oogenesis, these secretions become organized into three functional layers, each with a characteristic substructure. Follicle cells mold the shape of the hull spines even down to the petalloid tips that are characteristic of this group. Late in oogenesis the oocyte secretes the vitelline layer beneath the hull and the follicle cells break down and are sloughed off. Differences in the mechanisms of hull formation among chitons are providing a new set of morphological characters that may yield insight into chiton phylogeny. To our knowledge, this is the first description of micro-apocrine secretions during oogenesis in a mollusc, although it has been reported in other phyla.

Interaction between chromatoid bodies and mitochondria in neoblasts and gonial cells of the asexual and spontaneously sexualized planarian, Girardia (Dugesia) tigrina

Summary The interaction between chromatoid bodies and mitochondria in neoblasts of the asexually reproducing planarian Girardia (Dugesia) tigrina, as well as in oogonial cells of the spontaneously sexualized individual G. tigrina, was studied using transmission electron microscopy. Mitochondria-chromatoid body complexes (chromatoid bodies surrounded by several mitochondria) are typical of planarian neoblasts and oogonia. In many mitochondria contacting the chromatoid bodies in gonial cells, the outer mitochondrial membrane disappeared, and release of the mitochondrial matrix was observed. The mitochondial derivatives devoid of an outer membrane and initially containing cristae of the inner mitochondrial membrane apparently were integrated with the material of chromatoid bodies. These findings agree with our previous ultrastructural data on sea urchin, fish and holothurian gonial cells and also with the molecular evidence provided by other authors for the presence of mitochondrial ribosomal RNA in germline granules. It is proposed that the release of a mitochondrial matrix into the cytoplasm mediates the transport and incorporation of mitochondrial derivatives into chromatoid and germinal bodies where both mitochondrial and nuclear genome products are involved in structural organization and functioning of the macromolecular complex.

Is there a germ plasm in mouse oocytes

It was found that in the Graafian oocytes of laboratory mice Mus musculus the population of electron-dense bodies contains two patterns of structures. One of these, designated as cortical granules, originated from the Golgi complex and was surrounded by a membrane. The other was discovered as cristae-containing mitochondrial derivatives lacked an outer membrane. It was found that the mitochondrial derivatives underwent progressive condensation and transformed into electron-dense bodies similar to germinal bodies of metazoan animals. Based on examination of Graafian follicle oocytes from 5 female individuals, about 15% of electron-dense bodies were cortical granules. However, about 85% of electron-dense bodies were condensing mitochondrial derivatives transforming into electron-dense bodies.

Structure of the testis and changes shown during the annual reproductive cycle in Cucumaria japonica (Echinodermata: Holothuroidea)

Summary In the holothurian, Cucumaria japonica, deep invaginations of the germinal epithelium of the testis are formed during the period of active spermatogenesis (January-February) but are reduced in prespawning animals (August). The invaginations contain basal lamina which envelope the testis and separate the haemal sinus from the gonad lumen. They are lined with germinal epithelium. Nurse cells are not present within regions of the germinal epithelium associated with invaginations of the lamina. These regions are invested by spermatogenic cells only.