Biology subjects

Kremnyov, S. V.

Publications and source records attributed to Kremnyov, S. V..

4 recordsLinked to original sources

bioRxiv2023

Distribution of nematocytes differs in two types of gonophores in hydrozoan Sarsia lovenii.

Hydrozoan cnidarians are widely known for a diversity of life cycles. While some hydrozoan polyps produce medusae, in most species the gonophore remains attached to the polyp. Little is known about the mechanisms behind the loss of the medusal stage in hydrozoans. Hydrozoan Sarsia lovenii is a promising model for studying this issue. It is a polymorphic species with several haplogroups. One haplogroup produces attached eumedusoids and the other one buds free-swimming medusae. Here, we compared patterns of cell proliferation and distribution of nematocytes in medusoids, medusa buds and medusae of S. lovenii. Cell proliferation is absent from exumbrella of late medusa buds and medusae, but presumably i-cells proliferate in exumbrella of medusoids. In exumbrella of medusoids, we also observed evenly distributed nematocytes with capsules and expression of late nematogenesis-associated gene, Nowa. Nematocyte capsules and Nowa expression were also observed in exumbrella of medusa bud, but we did not detect prominent Nowa signal in the bell of developed medusa. It is also known that abundance of exumbrellar nematocysts signs immaturity in medusae of Sarsia genus. Our data demonstrate that nematocyte distribution and associated gene expression in medusoids resemble medusa buds rather than developed medusae. Thus, sexually mature medusoids exhibit juvenile somatic characters, demonstrating signs of neoteny. Research highlightsHydrozoan Sarsia lovenii has attached eumedusoids and free-swimming medusae. The distribution of nematocytes in eumedusoids resembles that in medusa buds. This may indicate neoteny of eumedusoids.

zoology↗

bioRxiv2023

Evolutionary history of the Brachyury gene in Hydrozoa: duplications, divergence and neofunctionalization.

Brachyury, a member of T-box gene family, is widely known for its major role in mesoderm specification in bilaterians. It is also present in non-bilaterian metazoans, such as cnidarians, where it acts as a component of an axial patterning system. In this study, we present a phylogenetic analysis of Brachyury genes within phylum Cnidaria, investigate differential expression and address a functional framework of Brachyury paralogs in hydrozoan Dynamena pumila. Our analysis indicates two duplication events of Brachyury in the cnidarian lineage: in the common ancestor of the Medusozoa clade and at the base of the class Hydrozoa. We designate result of the first step as Brachyury2 and of the second as Brachyury3. Brachyury1 and 2 display a conservative expression pattern marking the oral pole of the body axis in D. pumila. On the contrary, Brachyury3 expression was detected in scattered presumably nerve cells of the D. pumila larva. Pharmacological modulations indicated that Brachyury3 is not under regulation of cWnt signalling in contrast to the other two Brachyury genes. Divergence in expression patterns and regulation suggest neofunctionalization of Brachyury3 in hydrozoans.

developmental biology↗

bioRxiv2021

Robust phylogenetic position of the enigmatic hydrozoan, Margelopsis haeckelii revealed within the family Corymorphidae

The life-cycle and polyp morphology of representatives of Margelopsidae are very different from all other species in the hydrozoan clade Aplanulata. Their evolutionary origin and phylogenetic position has been the subject of significant speculation. A recent molecular study based only on COI data placed Margelopsidae as a sister group to all Aplanulata, an unexpected result because margelopsid morphology suggests affiliation with Tubulariidae or Corymorphidae. Here we used multigene analyses, including nuclear (18S rRNA and 28S rRNA) and mitochondrial (16S rRNA and COI) markers of the hydroid stage of the margelopsid species Margelopsis haeckelii Hartlaub, 1897 and the medusa stage of Margelopsis hartlaubii Browne, 1903 to resolve their phylogenetic position with respect to other hydrozoans. Our data provide strong evidence that M. haeckelii, the type species of Margelopsis, is a member of the family Corymorphydae. In contrast, M. hartlaubii Browne, 1903 is sister to Plotocnide borealis Wagner, 1885, a member of Boreohydridae. These results invalidate the family Margelopsidae. The phylogenetic signal of polyp and medusa stages is discussed in light of concept of inconsistent evolution and molecular phylogenetic analysis.

zoology↗

bioRxiv2021

Apolar mode of gastrulation leads to the formation of polarized larva in a marine hydroid, Dynamena pumila

BackgroundIn almost all metazoans examined to this respect, the axial patterning system based on canonical Wnt (cWnt) signaling operates throughout the course of development. In most metazoans, gastrulation is polar, and embryos develop morphological landmarks of axial polarity, such as blastopore under control/regulation from Wnt signaling. However, in many cnidarian species, gastrulation is morphologically apolar. The question remains whether [c]Wnt signaling providing the establishment of a body axis controls morphogenetic processes involved in apolar gastrulation. ResultsIn this study, we focused on the embryonic development of Dynamena pumila, a cnidarian species with apolar gastrulation. We thoroughly described cell behavior, proliferation, and ultrastructure and examined axial patterning in the embryos of this species. We revealed that the first signs of morphological polarity appear only after the end of gastrulation, while molecular prepatterning of the embryo does exist during gastrulation. We have shown experimentally that in D. pumila, the morphological axis is highly robust against perturbations in cWnt activity. ConclusionOur results suggest that morphogenetic processes are uncoupled from molecular axial patterning during gastrulation in D. pumila. Investigation of D. pumila might significantly expand our understanding of the ways in which morphological polarization and axial molecular patterning are linked in Metazoa.

developmental biology↗