Vol 48, No 3 (2017)

The similarity between the calcium-activated signaling systems of oocytes and neuronal axon terminals has prompted us to test whether BASP1 and GAP-43 proteins, highly expressed in brain neurons, are present in oocytes. Using immunocytochemical techniques combined with confocal microscopy, we have for the first time demonstrated that both BASP1 and GAP-43 are present in mouse metaphase II (MII) oocytes and zygotes. BASP1 is localized to the plasma membrane and actin cortex of MII oocytes, which is similar to BASP1 distribution in neurons and other cell types. GAP-43 is generally regarded as a postmitotic membrane marker of nerve cells; however, GAP-43 in MII oocytes is associated with microtubules of the meiotic spindle. GAP-43 is also colocalized with γ-tubulin at the spindle poles (centrosomes) and at the discrete microtubule- organizing centers in the cytoplasm. The antibodies to Ser41-phosphorylated form of GAP-43 allowed for demonstration that GAP-43 in oocytes is subject to phosphorylation by protein kinase C. The presence of BASP1 and GAP-43 in oocytes is also confirmed by electrophoresis and western blotting. Microinjection of BASP1 (but not GAP-43) into the cytoplasm of mouse MII oocytes induces their exit from metaphase II arrest followed by parthenogenetic embryo development. This suggests putative BASP1 involvement in fertilization-induced oocyte activation, presumably, through regulation of local concentration of polyphosphoinositides in the plasma membrane. Recently it was found that GAP-43 is associated with centrosomes in asymmetrically dividing neuronal progenitors, which is similar to the localization of GAP-43 at the meiotic spindle and centrosomes in oocytes. Therefore we suggest that GAP-43 may be involved in regulation of spindle orientation and oocyte polarity.

The yolk syncytial layer (YSL) is a symplastic provisory system that forms at the early stages of embryogenesis of teleosts. The YSL serves morphogenetic, trophic, and immune functions. Despite its important role in development, data on the structure of YSL is scarce. In the present study, comparative histological research on the features of YSL structure in the development of larvae of four economically important species of Coregonidae (Salmoniformes)—Coregonus peled, Coregonus muksun, Coregonus nasus, and Stenodus leucichthys nelma—is presented. The YSL of the larvae of Coregonidae has a complex, differentiated structure. Functional regionalization of YSL cytoplasm, possibly determined by the specific features of nutrient assimilation, is typical for all aforementioned species. Cytoplasm that encircles a large oil globule appears striated. A division into an inner area, filled with yolk inclusions, and an outer, smoother homogeneous area, can be noted in the cytoplasm surrounding the yolk mass. The oil globule is retained after complete utilization of the yolk mass. The inequality of thickness of YSL along anteroposterior and dorsoventral axes also indicates the functional regionalization. The dorsomedial area of YSL, located under the intestine, is the least thick. Dorsolateral areas are strongly incrassated and envelop the intestine from two sides. Gigantic nuclei of exceptionally complex form are typical for YSL. Specific features apply to the form of YSL and its nuclei. Based on the obtained results, a fundamental similarity in organization of the YSL of larvae of the studied whitefishes can be concluded; however, its specific variations distinguishable on a histological level can be discussed.

Ultrastructures of in vitro microspore embryoids and in vivo zygotic embryos of spring wheat have been analyzed and compared. Along with the similarity of ultrastructural characteristics of embryoid and embryo cells at the corresponding developmental stages, some differences have been revealed. Unlike embryos, embryoid cells are characterized by lipid inclusions and numerous mitochondria with well-developed internal membranes. According to our hypothesis, lipids represent an alternative energy source required for active cell divisions in the forming embryoids. Unlike embryos, since the earliest developmental stages, embryoid cells accumulate a significant amount of starch and then utilize it during the organogenesis and germination. A conclusion has been made that embryoid cells create their own reserve of carbohydrates, which is then mobilized during their development. The concept of T.B. Batygina (1987, 1997, 2014) about the universal character of the plant morphogenesis in vivo, in situ, and in vitro has been confirmed. The prospects for the use of microspore embryoidogenesis in vitro as a model to study cytophysiological aspects of zygotic embryogenesis in vivo are discussed.

Regenerating segments in polychaetes offer a vivid example of epimorphic recovery of the lost organs and tissues. It is also a promising object for studying positional information and the mechanisms maintaining the body integrity. With the aim to develop a convenient standardized model, we described the dynamics of recovery of the major anatomical structures and created a staging system for the caudal regeneration in Alitta virens. In average the normal organization of the posterior body end is restored within 10 days after amputation (dpa). The whole regenerative process was divided into 5 stages: (1) wound healing (0–1 dpa), (2) blastema formation (1–2 dpa), (3) patterning and growth of the blastema (2–3 dpa), (4) differentiation of the first regenerated segment (3–5 dpa), (5) formation and differentiation of the subsequent 5–6 segments (5–10 dpa). The regeneration is carried out mainly by epimorphosis, although the elements of intercalary growth as well as the morphallactic transformation of the stump have been noted. Terminal structures of the pygidium (muscles of the anal sphincter, pygidial cavity, pygidial ring nerve, pygidial cirri) appear at stages 1–3, and then (from stage 3) the formation of new metameres begins in front of the pygidium. Differentiation of the first newborn segment is associated with the tissue remodeling in the last old segment. Formation of the next segments resembles accelerated postlarval growth. The neural elements of the regenerative bud are developing faster than the surrounding muscles. The neurites extending from the CNS and PNS come to the surface of the wound epithelium at stage 1. Later, nerve fibers from the CNS lengthen and thicken along with the growth of the regenerative bud. Ganglion, parapodial nerves, oblique muscles and coeloms of the first segment are detected at stage 4. Longitudinal muscles regenerate in anterior to posterior progression, being constantly in contact with the corresponding fibers of the old tissues. All other muscles differentiate from blastemal cells in isolation from the old musculature of the stump. Our data promote the further using of the posterior body end regeneration in A. virens as an experimental model for resolving crucial problems of developmental biology.

Retinoic acid (RA) plays an important role in vertebrate development and regeneration. RA signalling directly regulates the expression of Hox genes, being in this way involved in the patterning of the anterior-posterior (AP) axis of vertebrate embryos. So far the relationship between retinoic acid signalling and Hox genes has been shown only for chordates. In this study we incubated juvenile worms and regenerating worms of two polychaete species from the family Nereididae, Alitta virens and Platynereis dumerilii, with all-trans-retinal, the precursor of retinoic acid. Under the influence of all-trans-retinal the anterior expression boundary of Post2 Нох gene shifted towards the anterior end both in intact and in regenerating worms of both species. Our data indicate the existence of a relationship between RA signalling and Нох genes in Protostomia.

The aorta is a magistral artery, which has been traditionally looked upon as a vessel whose properties are invariable throughout its length. However, in the most recent decade, there have been accumulated data that provide evidence that different aorta sections arise from different embryonic origins and that the population of smooth muscle cells making up the vessel’s wall is, consequently, heterogenic. Tracing the fate of smooth muscle cells, the basic components of the vessel, with the aid of genetic marking methods revealed that the cells’ response to various factors is largely determined by the embryonic origin of a certain cell population. However, functional differences between the smooth muscle cells making up different aorta sections remain poorly understood. The aim of the current work was to compare the functional characteristics of the populations of aortic wall smooth muscle cells obtained from the aorta sections differing by their embryonic origin. Towards this end, we obtained smooth muscle cell cultures from the three aorta sections of linear rats, namely, the neural crest derived ascending thoracic aorta, the somites derived descending thoracic aorta, and splanchnic mesoderm derived abdominal aorta. Using immunocytochemistry and Western blotting, the cells from the different regions of aorta were compared on the basis of smooth muscle actin, vimentin, and SM22 content in them. Cell proliferation rate was estimated using the growth curves method. We have demonstrated that the three smooth muscle cell populations arising from different embryonic origins differ in their morphological characteristics as well as by smooth muscle actin and SM22 content. We have shown that smooth muscle cells from the ascending aorta proliferate more actively than the corresponding cells from the descending thoracic aorta. Thus, the functional properties of the populations of rat aortic smooth muscle cells are different and depend on the embryonic origin of the aorta section from which they were obtained.

The paper reports a light and electron microscopy study of the ultrastructure and oogenesis of germ-cell determinants in freshwater sponges Eunapius fragilis and Swartschewskia papyracea. For the first time, germinal granules surrounded by mitochondria, the ultrastructural signature of germinal plasma in a number of metazoan organisms, has been described in Porifera. Structural changes in germ determinants in the course of oogenesis have been described, and participation of mitochondria in the formation of the central component of germ cell determinants has been suggested.