The postanal tail of the enteropneust Saccoglossus kowalevskii is a ciliary creeping organ without distinct similarities to the chordate tail

Stach, Thomas; Kaul, Sabrina

doi:10.1111/j.1463-6395.2010.00462.x

Cited by 11 publications

(7 citation statements)

References 46 publications

(57 reference statements)

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“…6k, l ). Obvious differences are a lower number of gill slits and the presence of the postanal tail, a feature only present in juvenile acorn worms of the family Harrimaniidae (Cameron 2005 ; Stach and Kaul 2012 ). Scanning electron micrographs of the anterior tip of the proboscis show that the former ciliary tuft is degraded (Fig.…”

Section: Resultsmentioning

confidence: 99%

Neurogenesis in directly and indirectly developing enteropneusts: of nets and cords

et al. 2015

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Concerning the evolution of deuterostomes, enteropneusts (acorn worms) occupy a pivotal role as they share some characteristics with chordates (e.g., tunicates and vertebrates) but are also closely related to echinoderms (e.g., sea urchin). The nervous system in particular can be a highly informative organ system for evolutionary inferences, and advances in fluorescent microscopy have revealed overwhelming data sets on neurogenesis in various clades. However, immunocytochemical descriptions of neurogenesis of juvenile enteropneusts are particularly scarce, impeding the reconstruction of nervous system evolution in this group. We followed morphogenesis of the nervous system in two enteropneust species, one with direct (Saccoglossus kowalevskii) and the other with indirect development (Balanoglossus misakiensis), using an antibody against serotonin and electron microscopy. We found that all serotonin-like immunoreactive (LIR) neurons in both species are bipolar ciliary neurons that are intercalated between other epidermal cells. Unlike the tornaria larva of B. misakiensis, the embryonic nervous system of S. kowalevskii lacks serotonin-LIR neurons in the apical region as well as an opisthotroch neurite ring. Comparative analysis of both species shows that the projections of the serotonin-LIR somata initially form a basiepidermal plexus throughout the body that disappears within the trunk region soon after settlement before the concentrated dorsal and ventral neurite bundles emerge. Our data reveal a highly conserved mode of neurogenesis in enteropneusts that is independent of the developing mode and is inferred to be a common feature for Enteropneusta. Moreover, all detected serotonin-LIR neurons are presumably receptor cells, and the absence of serotonin-LIR interneurons from the enteropneust nervous system, which are otherwise common in various bilaterian central nervous systems, is interpreted as a loss that might have occurred already in the last common ancestor of Ambulacraria.

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Section: Resultsmentioning

confidence: 99%

Neurogenesis in directly and indirectly developing enteropneusts: of nets and cords

et al. 2015

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“…Thus, Brachyury homologues and their expression patterns were identified in the sea urchins Hemicentrotus pulcherrimus (Harada et al ), Strongylocentrotus purpuratus (Peterson et al ), Paracentrotus lividus (Croce et al ), and Lytechinus variegatus (Gross and McClay ); the starfish Asterina pectinifera (Shoguchi et al ); and the hemichordate Ptychodera flava (Tagawa et al ; Peterson et al ). Brachyury expression has recently been observed in the tailbud (anus) area of hemichordate juveniles (Tagawa et al unpublished data), reminiscent of vertebrate Brachyury expression in the tailbud, although a recent electron microscopy showed that the hemichordate postanal tail is a ciliary creeping organ without distinct similarities to the chordate tail (Stach and Kaul ).…”

Section: Brachyury: a Key Transcription Factor For Notochord Formationmentioning

confidence: 99%

How was the notochord born?

Satoh

Tagawa

Takahashi

2012

Evolution and Development

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More than 550 million years ago, chordates originated from a common ancestor shared with nonchordate deuterostomes by developing a novel type of larva, the "tadpole larva." The notochord is the supporting organ of the larval tail and the most prominent feature of chordates; indeed, phylum Chordata is named after this organ. In this review, we discuss the molecular mechanisms involved in the formation of the notochord over the course of chordate evolution with a special emphasis on a member of T-box gene family, Brachyury. Comparison of the decoded genome of a unicellular choanoflagellate with the genomes of sponge and cnidarians suggests that T-box gene family arose at the time of the evolution of multicellular animals. Gastrulation is a morphogenetic movement that is essential for the formation of two- or three-germ-layered embryos. Brachyury is transiently expressed in the blastopore (bp) region, where it confers on cells the ability to undergo invagination. This process is involved in the formation of the archenteron in all metazoans. This is a "primary" function of Brachyury. During the evolution of chordates, Brachyury gained an additional expression domain at the dorsal midline region of the bp. In this new expression domain, Brachyury served its "secondary" function, recruiting another set of target genes to form a dorsal axial organ, notochord. The Wnt/β-catenin, BMP/Nodal, and FGF-signaling pathways are involved in the transcriptional activation of Brachyury. We discuss the molecular mechanisms of Brachyury secondary function in the context of the dorsal-ventral (D-V) inversion theory and the aboral-dorsalization hypothesis. Although the scope of this review requires some degree of oversimplification of Brachyury function, it is beneficial to facilitate studies on the notochord formation, a central evolutionary developmental biology problem in the history of metazoan evolution, pointed out first by Alexander Kowalevsky.

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“…Considered in conjunction with its morphology and position, we hypothesize that Gyaltsenglossus was able to use this structure for attachment as an anchor to access the water column to feed on plankton (Figure 4) and possibly for locomotion. The most comparable structure in extant acorn worms is the postanal tail of juvenile harrimanids [19,27], which are glandular, ciliated, and used for attachment and locomotion [19,27,31] (Figure 3B). This tail was lost in derived crown-group enteropneusts (spengelids, ptychoderids, and torquaratorids), and is believed to be a homolog of the pterobranch stalk [10,19,25,31].…”

Section: Discussionmentioning

confidence: 99%