Biomedical subjects

Katja Seipel

Publications and source records attributed to Katja Seipel.

8 recordsLinked to original sources

PubMed2006

BMP2/4 and BMP5-8 in jellyfish development and transdifferentiation.

Bone morphogenetic proteins (BMPs) have key roles in gastrulation, mesoderm induction and axial patterning. The multitude of bilaterian BMPs employed in these morphogenetic processes contrasts starkly with the scarcity of BMPs in Cnidaria, the most basal eumetazoan phylum. In coral, sea anemone and hydra species, BMPs have been found to be associated with larval and polyp axial patterning. In the hydrozoan jellyfish Podocoryne (Hydractinia) carnea the BMP2/4 and BMP5-8 genes are expressed unilaterally in the larva, corroborating a possible role in larval axial development. With the focal area of BMP expression in the anterior region, however, the jellyfish larva may have a developmental reversal of spatial polarity compared to the anthozoan larva. In medusa development, BMP genes are expressed in divergent expression territories within the presumptive radial canals and in various parts of the endoderm, indicative of an involvement in mesoderm patterning and gastrovascular system formation reminiscent of bilaterian BMP functions. In addition, the BMP2/4 and BMP5-8 genes may play roles in wound response and dedifferentiation or S-phase re-entry, respectively, as the former is expressed in striated muscle cells immediately after excision from the bell and the latter in the initial phase of muscle cell transdifferentiation.

Amino Acid Sequence↗

PubMed2006

Mesodermal anatomies in cnidarian polyps and medusae.

The cellular and developmental analysis of evolutionary-conserved genes directing bilaterian mesodermal and myogenic cell fate previously identified the hydromedusan entocodon and its differentiation product, the striated muscle, as mesodermal derivatives. In view of these findings we presented a hypothesis disputing the diploblast classification of cnidarians without providing further explanations for the apparent diploblasty of the polyp stage and the formation of the subepidermal striated muscle in those Medusozoa lacking the entocodon nodule (Seipel and Schmid, 2005). Hence we carried out a systematic review of the histological and experimental evidence for mesodermal differentiations in cnidarians. In anthozoan and scyphozoan but not in hydrozoan polyps the presumptive mesodermal elements include amoeboid cells, the mesentery retractor muscles and scleroblasts, all of which are embedded or deeply rooted in the extracellular matrix (mesoglea) and derive from the ectoblastemal cells invading the extracellular matrix from the gastrulation site during or shortly after endoderm formation. These data lend further support to the cnidarian mesodermate hypothesis, whereby cnidarians and bilaterians share a common triploblast ancestor, the Urtriploblast, a small, motile, possibly medusa-like organism that did not feature a sessile polyp stage in its life cycle. As a consequence the diploblasty of the hydrozoan polyps may represent a derived morphology resulting from heterochronic modulations of the gastrulation process after endoderm formation.

Animals↗

PubMed2005

Evolution of striated muscle: jellyfish and the origin of triploblasty.

The larval and polyp stages of extant Cnidaria are bi-layered with an absence of mesoderm and its differentiation products. This anatomy originally prompted the diploblast classification of the cnidarian phylum. The medusa stage, or jellyfish, however, has a more complex anatomy characterized by a swimming bell with a well-developed striated muscle layer. Based on developmental histology of the hydrozoan medusa this muscle derives from the entocodon, a mesoderm-like third cell layer established at the onset of medusa formation. According to recent molecular studies cnidarian homologs to bilaterian mesoderm and myogenic regulators are expressed in the larval and polyp stages as well as in the entocodon and derived striated muscle. Moreover striated and smooth muscle cells may have evolved directly and independently from non-muscle cells as indicated by phylogenetic analysis of myosin heavy chain genes (MHC class II). To accommodate all evidences we propose that striated muscle-based locomotion coevolved with the nervous and digestive systems in a basic metazoan Bauplan from which the ancestors of the Ctenophora (comb jellyfish), Cnidaria (jellyfish and polyps), as well as the Bilateria are derived. We argue for a motile tri-layered cnidarian ancestor and a monophyletic descent of striated muscle in Cnidaria and Bilateria. As a consequence, diploblasty evolved secondarily in cnidarian larvae and polyps.

Animals↗

PubMed2005

The homeobox gene Msx in development and transdifferentiation of jellyfish striated muscle.

Bilaterian Msx homeobox genes are generally expressed in areas of cell proliferation and in association with multipotent progenitor cells. Likewise, jellyfish Msx is expressed in progenitor cells of the developing entocodon, a cell layer giving rise to the striated and smooth muscles of the medusa. However, in contrast to the bilaterian homologs, Msx gene expression is maintained at high levels in the differentiated striated muscle of the medusa in vivo and in vitro. This tissue exhibits reprogramming competence. Upon induction, the Msx gene is immediately switched off in the isolated striated muscle undergoing transdifferentiation, to be upregulated again in the emerging smooth muscle cells which, in a stem cell like manner, undergo quantal cell divisions producing two cell types, a proliferating smooth muscle cell and a differentiating nerve cell. This study indicates that the Msx protein may be a key component of the reprogramming machinery responsible for the extraordinary transdifferentation and regeneration potential of striated muscle in the hydrozoan jellyfish.

Amino Acid Sequence↗

PubMed2004

Developmental and evolutionary aspects of the basic helix-loop-helix transcription factors Atonal-like 1 and Achaete-scute homolog 2 in the jellyfish.

The close functional link of nerve and muscle cells in neuromuscular units has led to the hypothesis of a common evolutionary origin of both cell types. Jellyfish are well suited to evaluate this theory since they represent the most basal extant organisms featuring both striated muscle and a nervous system. Here we describe the structure and expression of two novel genes for basic helix-loop-helix (bHLH) transcription factors, the Achaete-scute B family member Ash2 and the Atonal-like gene Atl1, in the hydrozoan jellyfish Podocoryne carnea. Ash2 is expressed exclusively in larval and adult endoderm cells and may be involved in differentiation of secretory cells. Atl1 expression is more widespread and includes the developing striated muscle as well as mechanosensory and nerve cell precursors in the medusa tentacles. Moreover, Atl1 expression is upregulated in proliferating nerve cell precursors arising from adult striated muscle cells by transdifferentiation in vitro. Likewise, the neuronal marker gene NP coding for the RFamide neuropeptide is expressed not only in mature nerve cells but also transiently in the developing muscle. The molecular evidence is concurrent to the hypothesis that muscle and nerve cells are closely linked in evolution and derive from a common myoepithelial precursor.

Amino Acid Sequence↗

PubMed2004

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.

Amino Acid Sequence↗

PubMed2004

The germ line and somatic stem cell gene Cniwi in the jellyfish Podocoryne carnea.

In most animal phyla from insects to mammals, there is a clear division of somatic and germ line cells. This is however not the case in plants and some animal phyla including tunicates, flatworms and the basal phylum Cnidaria, where germ stem cells arise de novo from somatic cells. Piwi-like genes represent essential stem cell genes in diverse multicellular organisms. The cnidarian Piwihomolog Cniwiwas cloned from Podocoryne carnea, a hydrozoan with a full life cycle. CniwiRNA is present in all developmental stages with highest levels in the egg and the medusa. In the adult medusa, Cniwi expression is prominent in the gonads where it likely functions as a germ stem cell gene. The gene is also expressed, albeit at low levels, in differentiated somatic cells like the striated muscle of the medusa. Isolated striated muscle cells can be induced to transdifferentiate into smooth muscle cells which proliferate and differentiate into nerve cells. Cniwi expression is upregulated transiently after induction of transdifferentiation and again when the emerging smooth muscle cells proliferate and differentiate. The continuous low-level expression of an inducible stem cell gene in differentiated somatic cells may underlie the ability to form medusa buds from polyp cells and explain the extraordinary transdifferentation and regeneration potential of Podocoryne carnea.

Aging↗

PubMed2003

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.

Amino Acid Sequence↗