V. V. Isaeva

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.

Topological singularities and symmetry breaking in development

The review presents a topological interpretation of some morphogenetic events through the use of well-known mathematical concepts and theorems. Spatial organization of the biological fields is analyzable in topological terms. Topological singularities inevitably emerging in biological morphogenesis are retained and transformed during pattern formation. It is the topological language that can provide strict and adequate description of various phenomena in developmental and evolutionary transformations. The relationship between local and global orders in metazoan development, i.e., between local morphogenetic processes and integral developmental patterns, is established. A topological inevitability of some developmental events through the use of classical topological concepts is discussed. This methodology reveals a topological imperative as a certain set of topological rules that constrains and directs embryogenesis. A breaking of spatial symmetry of preexisting pattern plays a critical role in biological morphogenesis in development and evolution.

vasa-related genes and their expression in stem cells of colonial parasitic rhizocephalan barnacle Polyascus polygenea (Arthropoda: Crustacea: Cirripedia: Rhizocephala)

vasa (vas)‐related genes are members of the DEAD‐box protein family and are expressed in the germ cells of many Metazoa. We cloned vasa‐related genes (PpVLG, CpVLG) and other DEAD‐box family related genes (PpDRH1, PpDRH2, CpDRH, AtDRHr) from the colonial parasitic rhizocephalan barnacle Polyascus polygenea, the non‐colonial Clistosaccus paguri (Crustacea: Cirripedia: Rhizocephala), and the parasitic isopodan Athelgis takanoshimensis (Crustacea: Isopoda). The colonial Polyascus polygenea, a parasite of the coastal crabs Hemigrapsus sanguineus and Hemigrapsus longitarsis was used as a model object for further detailed investigations. Phylogenetic analysis suggested that PpVLG and CpVLG are closely related to vasa‐like genes of other Arthropoda. The rest of the studied genes form their own separate branch on the phylogenetic tree and have a common ancestry with the p68 and PL10 subfamilies. We suppose this group may be a new subfamily of the DEAD‐box RNA helicases that is specific for parasitic Crustacea. We found PpVLG and PpDRH1 expression products in stem cells from stolons and buds of internae, during asexual reproduction of colonial P. polygenea, and in germ cells from sexually reproducing externae, including male spermatogenic cells and female oogenic cells.

Stem cells in the reproductive strategy of colonial rhizocephalan crustaceans (Crustacea: Cirripedia: Rhizocephala)

Summary In vivo, histological, histochemical, immunochemical and ultrastructural investigations were performed of the colonial internae of Peltogasterella gracilis, Polyascus (Sacculina) polygenea, and Thylacoplethus isaevae (all infesting decapods). It was shown that asexual reproduction in these species occurs through the budding of stolon-like structures. Undifferentiated stem cells were found inside the stolons. They take part in the morphogenesis of the earliest buds, and later migrate to the developing ovary as primary germ cells. The stem cells in P. polygenea, P. gracilis and Th. isaevae selectively express alkaline phosphatase activity, a well known histochemical marker for mammalian embryonic stem cells in vivo and in vitro. It is shown in P. gracilis that stem cells also selectively express proliferating cell nuclear antigen (PCNA), a cellular marker for cell reproduction. The reproductive strategy in colonial rhizocephalans includes a three-level cascade: asexual reproduction by budding in interna; repeated development of multiple externae; and, in some cases, repeated cycles of sexual reproduction in each externa, resulting in large numbers of hatching larvae and allowing the parasite to infest a large proportion of the host population. Thus, sexual and asexual generations alternate in the life-cycle of the colonial species; stem cells evidently contribute the source of cells in asexual as well as sexual reproduction.

Morphofunctional organization of reserve stem cells providing for asexual and sexual reproduction of invertebrates

Published and original data indicating evolutionary conservation of the morphofunctional organization of reserve stem cells providing for asexual and sexual reproduction of invertebrates are reviewed. Stem cells were studied in representatives of five animal types: archeocytes in sponge Oscarella malakhovi (Porifera), large interstitial cells in colonial hydroid Obelia longissima (Cnidaria), neoblasts in an asexual race of planarian Girardia tigrina (Platyhelmintes), stem cells in colonial rhizocephalans Peltogasterella gracilis, Polyascus polygenea, and Thylacoplethus isaevae (Arthropoda), and colonial ascidian Botryllus tuberatus (Chordata). Stem cells in animals of such diverse taxa feature the presence of germinal granules, are positive for proliferating cell nuclear antigen, demonstrate alkaline phosphatase activity (a marker of embryonic stem cells and primary germ cells in vertebrates), and rhizocephalan stem cells express the vasa-like gene (such genes are expressed in germline cells of different metazoans). The self-renewing pool of stem cells is the cellular basis of the reproductive strategy including sexual and asexual reproduction.

The diversity of ontogeny in animals with asexual reproduction and plasticity of early development

Diversity of blastogenesis and embryogenesis in animals with different reproductive strategy and different variants of the specification of germ lineage cells, defined in the literature as preformation, epigenesis, and somatic embryogenesis, is discussed. In the course of somatic embryogenesis (or, more precisely, blastogenesis), the oozooid that has developed from the egg is naturally cloning and forms numerous genetically and morphologically identical clonal individuals or modular units of a colony. This cloning results in amplification of the parent genotype; the subsequent sexual reproduction provides for genetic recombination, and the emergence of a huge number of larvae with dispersal function provides for reproductive success. In invertebrates that reproduce asexually, no isolation of the germ cell lineage takes place; the population of stem cells capable of realizing the complete developmental program, which includes gametogenesis and blastogenesis, is represented by a diaspora of cells dispersed in the organism and possessing evolutionarily conservative features of morphofunctional organization typical to cells of the germ lineage. The plasticity of early animal embryogenesis is revealed in experiments with embryonic cells cultivated in vitro. Asexual reproduction emerged repeatedly in the course of metazoan evolution; blastogenesis in animals of different taxa is more variable and less conservative than embryogenesis, but the integration of blastogenesis into the process of early embryogenesis undermines the conservatism of embryonic development.

Stem cells in asexual reproduction of the colonial ascidian Botryllus tubaratus (Tunicata: Ascidiacea)

Histological, cytochemical and ultrastructure research on the budding of the colonial ascidian Botryllus tuberatus aimed at searching for stem cells was performed. A dense mass of undifferentiated cells and the connection of the outer epidermal and inner atrial epithelia were revealed for the first time in the early buds of B. tuberatus. Undifferentiated cells revealed in the early buds and vascular system of the colony had morphological features of the stem and primary germ cells of metazoans. Intensive expression of alkaline phosphatase, the cytochemical marker of embryonal stem and primary germ cells of vertebrate animals, was revealed in developing buds and in some cells of the hematocyte population. Based on the literature and the author’s data it is hypothesized that the self-renewing pool of stem cells of the colonial ascidian B. tuberatus is the cellular basis of its reproductive strategy, including both sexual and asexual reproduction.

Rhizocephalan Barnacles—Parasites of Commercially Important Crabs and Other Decapods

Data are presented about the invasion level of commercially important crabs in the Sea of Okhotsk by rhizocephalan barnacles. Some general information concerning the structure, life cycle, and reproductive strategy of the parasitizing rhizocephalans and the effect on the Decapoda host. Practical recommendations have been proposed to decrease the infestation level in populations of commercially important crabs and to prevent parasitization of healthy populations.

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.

Effects of the Briarosaccus callosus Infestation on the Commercial Golden King Crab Lithodes aequispina

Commercial crab populations off the Kamchatka coasts are infested to a considerable degree by the rhizocephalan parasite Briarosaccus callosus: of 769 Lithodes aequispina males examined, 43 (5.7%) were parasitized. Infestations result in the feminization of the crabs, a significant decrease in the cheliped length, and a significant decrease in the carapace length and width. We suggest that commercial selection of healthy males, and the returning of unsuitable crabs, including infested ones, back into the sea, results in an increase of the proportion of infested crabs in the population, their elimination from reproduction, and, eventually, the gradual degradation of a whole population. To minimize as far as possible the negative effects of commercial crab harvesting, all infested crab specimens caught must be destroyed, either aboard or elsewhere, instead of throwing them back into the sea.