Hemichordata

Kaul-Strehlow, Sabrina; Röttinger, Éric

doi:10.1007/978-3-7091-1856-6_2

Cited by 18 publications

(16 citation statements)

References 137 publications

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“…Next, we ask whether this shared pattern is also apparent in the tornaria larva of S. californicum or specific to the adult form. [8][9][10][11][12]. The expression patterns of dlx, foxQ2-1, six3, and otx resemble those described at similar stages in P. flava, another hemichordate species with indirect development [21][22][23][24].…”

Section: Comparing Ap Patterning Between Adult and Larval Life Historsupporting

confidence: 49%

“…The ectoderm comprises an anterior sensory organ (the apical organ), a looped circum-oral ciliary band used in feeding and swimming, and a posterior ciliary band (the telotroch) used for locomotion at later developmental stages [10,11]. In contrast, the juvenile enteropneust is a benthic deposit-feeder with a muscular anterior proboscis used in digging and feeding, a collar, and a long trunk divided into discrete functional regions along the anteroposterior (AP) axis [12]. This report describes the first developmental study in the spengelid Schizocardium californicum [2], a temperate, indirect developing species from Morro Bay, CA.…”

Section: Resultsmentioning

confidence: 98%

“…The spatial relationships between these patterns are strikingly similar to S. kowalevskii [13] (and other bilaterians [25]). Genes with posterior expression limits in the collar and collar/trunk boundary in adults are detected in more posterior domains ( Figure 2C, [8][9][10][11][12], in the presumptive circum-oral ciliary band (otx), in broad domains of general ectoderm (lim1/ 5, pax6, and emx), or in both (irx). Gbx remains restricted in a narrow ectodermal band at the far posterior of the embryo around the blastopore/anus ( Figure 2C, 13).…”

Section: Comparing Ap Patterning Between Adult and Larval Life Histormentioning

confidence: 99%

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The Adult Body Plan of Indirect Developing Hemichordates Develops by Adding a Hox-Patterned Trunk to an Anterior Larval Territory

2017

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Many animals are indirect developers with distinct larval and adult body plans [1]. The molecular basis of differences between larval and adult forms is often poorly understood, adding a level of uncertainty to comparative developmental studies that use data from both indirect and direct developers. Here we compare the larval and adult body plans of an indirect developing hemichordate, Schizocardium californicum [2]. We describe the expression of 27 transcription factors with conserved roles in deuterostome ectodermal anteroposterior (AP) patterning in developing embryos, tornaria larvae, and post-metamorphic juveniles and show that the tornaria larva of S. californicum is transcriptionally similar to a truncated version of the adult. The larval ectoderm has an anterior molecular signature, while most of the trunk, defined by the expression of hox1-7, is absent. Posterior ectodermal activation of Hox is initiated in the late larva prior to metamorphosis, in preparation for the transition to the adult form, in which the AP axis converges on a molecular architecture similar to that of the direct developing hemichordate Saccoglossus kowalevskii. These results identify a molecular correlate of a major difference in body plan between hemichordate larval and adult forms and confirm the hypothesis that deuterostome larvae are "swimming heads" [3]. This will allow future comparative studies with hemichordates to take into account molecular differences caused by early life history evolution within the phylum. Additionally, comparisons with other phyla suggest that a delay in trunk development is a feature of indirect development shared across distantly related phyla.

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Section: Comparing Ap Patterning Between Adult and Larval Life Historsupporting

confidence: 49%

Section: Resultsmentioning

confidence: 98%

Section: Comparing Ap Patterning Between Adult and Larval Life Histormentioning

confidence: 99%

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The Adult Body Plan of Indirect Developing Hemichordates Develops by Adding a Hox-Patterned Trunk to an Anterior Larval Territory

2017

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“…The central nervous system of B. misakiensis including the collar cord become morphologically distinct in early settled juveniles, indicating that neurogenic patterning of the collar cord starts in metamorphosing larvae [18]. In contrast, the larval nervous system (apical organ and neurite bundles of the ciliary bands) are independent of the adult nervous system and degrade during metamorphosis and settlement [7, 16, 19]. Therefore, we focused on the expression patterns in metamorphosing larvae and early juveniles.…”

Section: Resultsmentioning

confidence: 99%

“…Schizocardium californicum) and Ptychoderidae (e.g. Balanoglossus spp., Ptychodera flava) [7]. Harrimaniid species develop directly into the juvenile worm, whereas spengelid and ptychoderid enteropneusts develop indirectly via a specific larval type, the tornaria.…”

Section: Introductionmentioning

confidence: 99%

Neuronal patterning of the tubular collar cord is highly conserved among enteropneusts but dissimilar to the chordate neural tube

Kaul

Urata

Praher

et al. 2017

Preprint

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The dorsal neural tube of chordates and the ventral nerve cord of annelids exhibit a similar molecular mediolateral architecture. Accordingly, the presence of such a complex nervous system (CNS) has been proposed for their last common ancestor. Members of Enteropneusta, a group of non-chordate deuterostomes, possess a less complex CNS including a hollow neural tube, whereby homology to its chordate counterpart remains elusive. Since the majority of data on enteropneusts stem from Saccoglossus kowalevskii, a derived direct-developer, we investigated expression of key neuronal patterning genes in the indirect-developer Balanoglossus misakiensis.The collar cord of B. misakiensis shows anterior Six3/6 and posterior Otx + engrailed expression, in a region corresponding to the chordate brain. Neuronal Nk2.1/Nk2.2 expression is absent. Interestingly, we found median Dlx and lateral Pax6 expression domains, i.e., a condition that is reversed compared to chordates.Comparative analyses reveal that CNS patterning is highly conserved among enteropneusts. BmiDlx and BmiPax6 have no corresponding expression domains in the chordate brain, which may be indicative of independent acquisition of a tubular CNS in Enteropneusta and Chordata. Moreover, mediolateral architecture varies considerably among chordates and enteropneusts, questioning the presence of a vertebrate-like patterned nervous system in the last common deuterostome ancestor.

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Ambulacrarians and the Ancestry of Deuterostome Nervous Systems

Formery

Schubert

Croce

2019

Results and Problems in Cell Differentiation

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The evolutionary origin and history of metazoan nervous systems has been at the heart of numerous scientific debates for well over a century. This has been a particularly difficult issue to resolve within the deuterostomes, chiefly due to the distinct neural architectures observed within this group of animals. Deuterostomes feature indeed central nervous systems, apical organs, nerve cords and basiepidermal nerve nets. Comparative analyses investigating the anatomy and molecular composition of deuterostome nervous systems have nonetheless succeeded in identifying a number of shared and derived features. These analyses have led to the elaboration of diverse theories about the origin and evolutionary elaboration of deuterostome nervous systems. Here, we provide an overview of these distinct theories. Further, we argue that deciphering the adult nervous systems of representatives of all deuterostome phyla, including echinoderms, which have long been neglected in this type of surveys, will ultimately provide answers to the questions of the ancestry and evolution of deuterostome nervous systems.

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Hemichordata

Cited by 18 publications

References 137 publications

The Adult Body Plan of Indirect Developing Hemichordates Develops by Adding a Hox-Patterned Trunk to an Anterior Larval Territory

The Adult Body Plan of Indirect Developing Hemichordates Develops by Adding a Hox-Patterned Trunk to an Anterior Larval Territory

Neuronal patterning of the tubular collar cord is highly conserved among enteropneusts but dissimilar to the chordate neural tube

Ambulacrarians and the Ancestry of Deuterostome Nervous Systems

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