Nathalie Yanze

Evolutionary aspects of developmentally regulated helix-loop-helix transcription factors in striated muscle of jellyfish

The function of basic helix-loop-helix (bHLH) proteins in cell differentiation was shown to be conserved from Drosophila to vertebrates, exemplified by the function of MyoD in striated muscle differentiation. In phylogeny striated muscle tissue appears first in jellyfish and the question of its evolutionary position is controversially discussed. For this reason we have studied the developmental role of myogenic bHLH genes in medusa development. Based on their dimerization ability, four genes of the bHLH family of transcription factors were isolated from the hydrozoan jellyfish Podocoryne carnea. While the proteins Id and Ash group with cognate family members from bilaterians, Net-like and JellyD1 could not be unequivocally classified. Id is expressed during the medusa budding process and in the adult medusa, Ash and Net-like are expressed in all life cycle stages from egg to adult medusa and JellyD1 is expressed in the blastula and gastrula stages, the planula larva, and in late medusa bud stages. The dimerization specificity, the expression pattern, and the conservation of two residues specific for a MyoD bHLH domain suggest that JellyD1 is related to an ancestral MyoD gene. Id, Net-like, and JellyD1 are either expressed in the entocodon or its derived tissues, the striated and smooth muscle of the bell. These findings strengthen the hypothesis that the entocodon is a mesoderm-like structure and that the common ancestor of Cnidaria and Bilateria was more complex in cell-type architecture and body organization than commonly thought.

nanos expression at the embryonic posterior pole and the medusa phase in the hydrozoan Podocoryne carnea

Summary The distinction between soma and germline is an important process in the development of animals with sexual reproduction. It is regulated by a number of germline‐specific genes, most of which appear conserved in evolution and therefore can be used to study the formation of the germline in diverged animal groups. Here we report the isolation of two orthologs of one such gene, nanos (nos), in the cnidarian Podocoryne carnea, a species with representative zoological features among the hydrozoans. By studying nos gene expression throughout the Podocoryne biphasic life cycle, we find that the germline differentiates exclusively during medusa development, whereas the polyp does not contribute to the process. An early widespread nos expression in developing medusae progressively refines into a mainly germline‐specific pattern at terminal stages of medusa formation. Thus, the distinction between germline and soma is a late event in hydrozoan development. Also, we show that the formation of the medusa is a de novo process that relies on active local cell proliferation and differentiation of novel cell and tissue types not present in the polyp, including nos‐expressing cells. Finally, we find nos expression at the posterior pole of Podocoryne developing embryos, not related to germline formation. This second aspect of nos expression is also found in Drosophila, where nos functions as a posterior determinant essential for the formation of the fly abdomen. This raises the possibility that nos embryonic expression could play a role in establishing axial polarity in cnidarians.

Homologs of vascular endothelial growth factor and receptor, VEGF and VEGFR, in the jellyfish Podocoryne carnea

Vascular endothelial growth factors (VEGF) are the major inducers of vasculogenesis and angiogenesis in vertebrates. Their effects are mediated by receptor tyrosine kinases of the VEGF receptor (VEGFR) family located on endothelial cells and include stimulation of cell survival, proliferation, migration, and tube formation as well as regulation of vascular permeability. Here, we report the presence of VEGF and VEGFR homologous genes in a basal invertebrate of the phylum Cnidaria. The marine jellyfish Podocoryne carnea features a gastrovascular system consisting of the feeding organ, or manubrium, the radial and ring canals, and the tentacle bulbs. Expression analysis indicates that both genes are involved in tentacle and gastrovascular canal formation, indicating an early recruitment of the VEGF signalling pathway for morphogenetic processes leading to tube formation in metazoans. The evolutionary origin of the VEGF signalling pathway resides in the common ancestor of the Cnidaria and Bilateria. Developmental Dynamics 231:303–312, 2004.

Integrin and talin in the jellyfish Podocoryne carnea.

We have isolated an integrin‐β and ‐α subunit from Podocoryne carnea (Cnidaria, Hydrozoa) and studied their expression in the life‐cycle and during cell migration, in vitro transdifferentiation and regeneration. Comparison of the integrin expression pattern with a Podocoryne talin homologue by RT‐PCR demonstrates that all three genes are maternal messages and continuously expressed in the life‐cycle, in medusa development and in all medusae tissues. In situ hybridisation experiments confirm co‐expression of both integrin subunits in the different life‐stages. Integrin expression was furthermore studied in isolated striated muscle induced to transdifferentiate to new cell types, or grafted on ECM where the muscle adheres and migrates. Integrin expression was maintained continuously throughout both processes. These results suggest that in Podocoryne carnea processes such as cell migration and differentiation are not controlled by up‐ or downregulation of alternative integrin subunits, but by a single integrin heterodimer which activates different downstream signalling cascades.

Basic leucine zipper transcription factors C/EBP and MafL in the hydrozoan jellyfish Podocoryne carnea

Members of the CCAAT/enhancer binding protein (C/EBP) and the Maf protein subfamilies have been characterized in a variety of bilaterian organisms. This is the first report of C/EBP and MafL genes in a basal organism, the hydrozoan jellyfish Podocoryne carnea. Transcripts of both genes are present in all life cycle stages: egg, embryo, larva, polyp, and medusa. During early development, both factors appear to regulate metamorphosis of the larva to the primary polyp. Both genes are also expressed in the striated muscle of the developing and adult medusa. During in vitro transdifferentiation of striated muscle cells to smooth muscle and nerve cells, C/EBP is continuously expressed, whereas MafL expression is turned off during transdifferentiation and reactivated when nerve cells differentiate. Thus, both factors may be involved in muscle and nerve cell differentiation. In the mature medusa both genes are also implicated in gametogenesis. Developmental and evolutionary aspects of the gene structures and expression patterns are discussed. Developmental Dynamics 230:392–402, 2004.