Discovery and characterization of a transient chaetal gland during the development of Capitella teleta (Sedentaria: Annelida).

Chaetae are among the most extensively studied structures in polychaetes, serving as a defining morphological trait for annelids. Capitella teleta stands out as one of the few established annelid models for developmental and morphological studies, thus receiving significant scholarly attention. In this study, we unveil a previously unnoticed glandular structure associated with chaetae within the larvae of C.

Sifting through the mud: A tale of building the annelid Capitella teleta for EvoDevo studies.

Over the last few decades, the annelid Capitella teleta has been used increasingly as a study system for investigations of development and regeneration. Its favorable properties include an ability to continuously maintain a laboratory culture, availability of a sequenced genome, a stereotypic cleavage program of early development, substantial regeneration abilities, and established experimental and functional genomics techniques. With this review I tell of my adventure of establishing the Capitella teleta as an emerging model and share examples of a few of the contributions our work has made to the fields of evo-devo and developmental biology.

Regeneration in the Segmented Annelid .

The segmented worms, or annelids, are a clade within the Lophotrochozoa, one of the three bilaterian superclades. Annelids have long been models for regeneration studies due to their impressive regenerative abilities. Furthermore, the group exhibits variation in adult regeneration abilities with some species able to replace anterior segments, posterior segments, both or neither.

Functional evidence that Activin/Nodal signaling is required for establishing the dorsal-ventral axis in the annelid .

The TGF-β superfamily comprises two distinct branches: the Activin/Nodal and BMP pathways. During development, signaling by this superfamily regulates a variety of embryological processes, and it has a conserved role in patterning the dorsal-ventral body axis. Recent studies show that BMP signaling establishes the dorsal-ventral axis in some mollusks.

Activin/Nodal signaling mediates dorsal-ventral axis formation before third quartet formation in embryos of the annelid .

Background: The clade of protostome animals known as the Spiralia (e.g., mollusks, annelids, nemerteans and polyclad flatworms) shares a highly conserved program of early development.

Functional role of pax6 during eye and nervous system development in the annelid Capitella teleta.

The transcription factor Pax6 is an important regulator of early animal development. Loss of function mutations of pax6 in a range of animals result in a reduction or complete loss of the eye, a reduction of a subset of neurons, and defects in axon growth. There are no studies focusing on the role of pax6 during development of any lophotrochozoan representative, however, expression of pax6 in the developing eye and nervous system in a number of species suggest that pax6 plays a highly conserved role in eye and nervous system formation.

Regeneration of the germline in the annelid Capitella teleta.

The germline is essential for sexual reproduction and survival of the species. In many metazoans, the developmental potential to generate a distinct germline is segregated from somatic cell lineages early in embryogenesis, suggesting that the unique features of the germline must be established from its onset. Previous studies suggest that germ cells cannot regenerate once removed from the embryo, but few animals have been experimentally tested.

Investigation into the cellular origins of posterior regeneration in the annelid .

Many animals can regenerate, although there is great diversity in regenerative capabilities. A major question in regenerative biology is determining the cellular source of newly formed tissue. The polychaete annelid, , can regenerate posterior segments following transverse amputation.

An organizing role for the TGF-β signaling pathway in axes formation of the annelid Capitella teleta.

Embryonic organizers are signaling centers that coordinate developmental events within an embryo. Localized to either an individual cell or group of cells, embryonic organizing activity induces the specification of other cells in the embryo and can influence formation of body axes. In the spiralian Capitella teleta, previous cell deletion studies have shown that organizing activity is localized to a single cell, 2d, and this cell induces the formation of the dorsal-ventral axis and bilateral symmetry.

Spatiotemporal regulation of nervous system development in the annelid .

Background: How nervous systems evolved remains an unresolved question. Previous studies in vertebrates and arthropods revealed that homologous genes regulate important neurogenic processes such as cell proliferation and differentiation. However, the mechanisms through which such homologs regulate neurogenesis across different bilaterian clades are variable, making inferences about nervous system evolution difficult.

Annelid models I: Capitella teleta.

Investigating development in a wide variety of organisms allows researchers to take advantage of both diverse and conserved evolutionary solutions that animals have made to solve a range of biological problems. Next generation sequencing and functional genomic techniques can now be applied to many animals, providing opportunities to study organisms whose biology offers advantages for tracking particular questions. Capitella teleta is an segmented annelid worm whose phylogenetic position, stable genome, environmental resiliency, early development and regeneration capabilities position it to provide insights to its evolutionary success.

A Stable Thoracic Hox Code and Epimorphosis Characterize Posterior Regeneration in Capitella teleta.

Regeneration, the ability to replace lost tissues and body parts following traumatic injury, occurs widely throughout the animal tree of life. Regeneration occurs either by remodeling of pre-existing tissues, through addition of new cells by cell division, or a combination of both. We describe a staging system for posterior regeneration in the annelid, Capitella teleta, and use the C.

Regulative capacity for eye formation by first quartet micromeres of the polychaete Capitella teleta.

The stereotypic cleavage pattern shared by spiralian embryos provides unique opportunities to compare mechanisms of cell fate specification of homologous blastomeres, and can give insights into how changes in fate may have influenced the evolution of novel structures and morphological diversity. The potential of cells to undergo regulation and the timing of cell fate specification were investigated during early development in the polychaete annelid, Capitella teleta. Targeted laser deletions of the first quartet micromeres were performed, with a focus on the eye-forming cells 1a and 1c.

Nervous system development in lecithotrophic larval and juvenile stages of the annelid Capitella teleta.

Background: Reconstructing the evolutionary history of nervous systems requires an understanding of their architecture and development across diverse taxa. The spiralians encompass diverse body plans and organ systems, and within the spiralians, annelids exhibit a variety of morphologies, life histories, feeding modes and associated nervous systems, making them an ideal group for studying evolution of nervous systems.

Results: We describe nervous system development in the annelid Capitella teleta (Blake JA, Grassle JP, Eckelbarger KJ.

Variation in spiralian development: insights from polychaetes.

Spiralian development is characterized by the conservation of spindle orientation and cell geometry during early cleavage stages, as well as features of the ultimate fates of identified cells. This complex set of characters is shared by a number of animal lineages including nemerteans, polyclad platyhelminthes, annelids and mollusks. How a similar, highly stereotypical cleavage program can give rise to such diversity of larval and adult forms has intrigued researchers for many years.

Molecular conservation of metazoan gut formation: evidence from expression of endomesoderm genes in Capitella teleta (Annelida).

Background: Metazoan digestive systems develop from derivatives of ectoderm, endoderm and mesoderm, and vary in the relative contribution of each germ layer across taxa and between gut regions. In a small number of well-studied model systems, gene regulatory networks specify endoderm and mesoderm of the gut within a bipotential germ layer precursor, the endomesoderm. Few studies have examined expression of endomesoderm genes outside of those models, and thus, it is unknown whether molecular specification of gut formation is broadly conserved.

An organizing activity is required for head patterning and cell fate specification in the polychaete annelid Capitella teleta: new insights into cell-cell signaling in Lophotrochozoa.

Many lophotrochozoans (i.e., molluscs, annelids, nemerteans, and polyclad flatworms) display a well-conserved early developmental program called spiral cleavage that contrasts with the high diversity of adult body forms present in this group.

Insights into bilaterian evolution from three spiralian genomes.

Current genomic perspectives on animal diversity neglect two prominent phyla, the molluscs and annelids, that together account for nearly one-third of known marine species and are important both ecologically and as experimental systems in classical embryology. Here we describe the draft genomes of the owl limpet (Lottia gigantea), a marine polychaete (Capitella teleta) and a freshwater leech (Helobdella robusta), and compare them with other animal genomes to investigate the origin and diversification of bilaterians from a genomic perspective. We find that the genome organization, gene structure and functional content of these species are more similar to those of some invertebrate deuterostome genomes (for example, amphioxus and sea urchin) than those of other protostomes that have been sequenced to date (flies, nematodes and flatworms).

Expression of the pair-rule gene homologs runt, Pax3/7, even-skipped-1 and even-skipped-2 during larval and juvenile development of the polychaete annelid Capitella teleta does not support a role in segmentation.

Background: Annelids and arthropods each possess a segmented body. Whether this similarity represents an evolutionary convergence or inheritance from a common segmented ancestor is the subject of ongoing investigation.

Methods: To investigate whether annelids and arthropods share molecular components that control segmentation, we isolated orthologs of the Drosophila melanogaster pair-rule genes, runt, paired (Pax3/7) and eve, from the polychaete annelid Capitella teleta and used whole mount in situ hybridization to characterize their expression patterns.

Cell lineage and fate map of the primary somatoblast of the polychaete annelid Capitella teleta.

Like most polychaete annelids, Capitella teleta (formerly Capitella sp. I) exhibits a highly stereotypic program of early development known as spiral cleavage. Animals with spiral cleavage have diverse body plans, and homologous embryonic cells can be readily identified among distantly related animals.

Somatic and germline expression of piwi during development and regeneration in the marine polychaete annelid Capitella teleta.

Background: Stem cells have a critical role during adult growth and regeneration. Germline stem cells are specialized stem cells that produce gametes during sexual reproduction. Capitella teleta (formerly Capitella sp.

Expression and phylogenetic analysis of the zic gene family in the evolution and development of metazoans.

Background: zic genes are members of the gli/glis/nkl/zic super-family of C2H2 zinc finger (ZF) transcription factors. Homologs of the zic family have been implicated in patterning neural and mesodermal tissues in bilaterians. Prior to this study, the origin of the metazoan zic gene family was unknown and expression of zic gene homologs during the development of early branching metazoans had not been investigated.

Expression of FoxA and GATA transcription factors correlates with regionalized gut development in two lophotrochozoan marine worms: Chaetopterus (Annelida) and Themiste lageniformis (Sipuncula).

Background: A through gut is present in almost all metazoans, and most likely represents an ancient innovation that enabled bilaterian animals to exploit a wide range of habitats. Molecular developmental studies indicate that Fox and GATA regulatory genes specify tissue regions along the gut tube in a broad diversity of taxa, although little is known about gut regionalization within the Lophotrochozoa. In this study, we isolated FoxA and GATA456 orthologs and used whole mount in situ hybridization during larval gut formation in two marine worms: the segmented, polychaete annelid Chaetopterus, which develops a planktotrophic larva with a tripartite gut, and the non-segmented sipunculan Themiste lageniformis, which develops a lecithotrophic larva with a U-shaped gut.

A comprehensive fate map by intracellular injection of identified blastomeres in the marine polychaete Capitella teleta.

Background: The polychaete annelid Capitella teleta (formerly Capitella sp. I) develops by spiral cleavage and has been the focus of several recent developmental studies aided by a fully sequenced genome. Fate mapping in polychaetes has lagged behind other spiralian taxa, because of technical limitations.