Evolution of the nervous system in <i>Paraphanostoma</i> (Acoela)

Raikova, Olga I.; Reuter, Maria; Gustafsson, Margaretha K. S.; Maule, Aaron G.; Halton, D W; Jondelius, Ulf

doi:10.1111/j.1463-6409.2004.00137.x

Cited by 58 publications

(83 citation statements)

References 30 publications

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“…The phylum Xenacoelomorpha is formed of animals with a relatively simple morphology, including that of their nervous systems (Raikova et al, 2000a;Raikova et al, 2000b;Raikova et al, 2004a;Raikova et al, 2004b;Achatz et al, 2013). Here, and for the first time using the genome sequence of members of this group, we have undertaken a systematic study of two superfamilies, the bHLHs and GPCRs, involved in the specification and the functionality of nerve tissue.…”

Section: Discussionmentioning

confidence: 99%

“…The Acoelomorph nervous system is a pertinent case here because it shows a high degree of variability within the group. It is characterized, according to some authors, by a low degree of centralization in the anterior domain (Raikova et al, 2004a;Hejnol and Martindale, 2008;Raikova, 2008). In the past 10 years, several studies using electron microscopy and immunocytochemistry have added to our knowledge of acoel neuroanatomy.…”

Section: The Acoel Nervous System In Contextmentioning

confidence: 99%

“…In the past 10 years, several studies using electron microscopy and immunocytochemistry have added to our knowledge of acoel neuroanatomy. The use of a single set of immunochemical markers, such as 5HT, GYIRF-amide and FMRF-amide has made analysis of the nervous system in this group possible (Raikova et al, 2004a;Achatz and Martinez, 2012). The systematic use of these immunochemical markers, in particular antibodies against 5-HT, led some authors to propose that acoels have a simple 'commissural brain' (Raikova, 2004c).…”

Section: The Acoel Nervous System In Contextmentioning

confidence: 99%

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The nervous system of Xenacoelomorpha: a genomic perspective

Perea-Atienza

Gavilán

Chiodin

et al. 2015

Journal of Experimental Biology

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Xenacoelomorpha is, most probably, a monophyletic group that includes three clades: Acoela, Nemertodermatida and Xenoturbellida. The group still has contentious phylogenetic affinities; though most authors place it as the sister group of the remaining bilaterians, some would include it as a fourth phylum within the Deuterostomia. Over the past few years, our group, along with others, has undertaken a systematic study of the microscopic anatomy of these worms; our main aim is to understand the structure and development of the nervous system. This research plan has been aided by the use of molecular/developmental tools, the most important of which has been the sequencing of the complete genomes and transcriptomes of different members of the three clades. The data obtained has been used to analyse the evolutionary history of gene families and to study their expression patterns during development, in both space and time. A major focus of our research is the origin of 'cephalized' (centralized) nervous systems. How complex brains are assembled from simpler neuronal arrays has been a matter of intense debate for at least 100 years. We are now tackling this issue using Xenacoelomorpha models. These represent an ideal system for this work because the members of the three clades have nervous systems with different degrees of cephalization; from the relatively simple sub-epithelial net of Xenoturbella to the compact brain of acoels. How this process of 'progressive' cephalization is reflected in the genomes or transcriptomes of these three groups of animals is the subject of this paper.

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Section: Discussionmentioning

confidence: 99%

Section: The Acoel Nervous System In Contextmentioning

confidence: 99%

Section: The Acoel Nervous System In Contextmentioning

confidence: 99%

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The nervous system of Xenacoelomorpha: a genomic perspective

Perea-Atienza

Gavilán

Chiodin

et al. 2015

Journal of Experimental Biology

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“…The nervous system, like cnidarians, is located basiepidermally, although in some acoel species nerve fibres are located subepidermally (Rieger et al 1991;Raikova et al 1998Raikova et al , 2004, and is connected to photoreceptive cells ('eyes') and epidermal sensory cells. Thus, if acoelomorphs resemble the urbilaterian, a dorsally or ventrally centralized nervous system is not part of the ground pattern of the Bilateria.…”

Section: The Phylogenetic Position Of the Acoelomorpha And Their Impamentioning

confidence: 99%

Acoel development supports a simple planula-like urbilaterian

Hejnol

Martindale

2008

Phil. Trans. R. Soc. B

145

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Molecular approaches to the study of development and evolution have had profound effects on our understanding of the nature of the evolutionary process. Developmental biologists became intoxicated with fanciful notions of reconstructing genetic pathways of morphogenesis while evolutionary biologists were sobered by the fallacy of reconstructing organismal relationships along increasing grades of morphological complexity. Increased taxon sampling and improvements in analytical techniques are providing a new approach and are forcing biologists to move past historical biases to allow more accurate mapping of morphological and developmental characters through evolutionary time. Here, we discuss the possible developmental and morphological features of the 'urbilaterian', the triploblastic animal with anterior-posterior and dorsoventral axes and predecessor of the protostome-deuterostome ancestor. We argue that this animal, with features resembling acoelomorph flatworms, was far simpler morphologically than the protostome-deuterostome ancestor despite possessing a nearly complete eubilaterian genome. We show that the deployment of some genes expected to pattern the protostome-deuterostome ancestor is not deployed in acoels in the predicted manner and thus might have been co-opted after the evolution of the urbilaterian. We also identify the developmental changes related to gastrulation that gave rise to the urbilaterian from a simpler cnidarian-like ancestor.

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“…Even closely related species display noticeably different NS organization: for instance, Faerlea glomerata Westblad, 1945 has a superficial weak barrel-shaped 5-HT immunoreactive (IR) brain (we follow the terminology suggested by Richter et al (2010)), while its close relative Avagina incola Leiper, 1902 displays a deep concentrated bridgeshaped brain (Reuter et al 2001b). The acoel NS variability was further demonstrated by the examination of seven representatives of Childiidae, a group of Acoela for which there is strongly corroborated phylogenetic hypothesis (Raikova et al 2004b). The study demonstrated that the brains in childiid species, although diverse in detail, still follow the same general pattern, and the complexity of this pattern progressively increases in accordance with the phylogenetic tree.…”

Section: Introductionmentioning

confidence: 89%

The plastic nervous system of Nemertodermatida

2015

Self Cite

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Nemertodermatida are microscopic marine worms likely to be the sister group to acoels, forming with them the earliest extant branch of bilaterian animals, although their phylogenetic position is debated. The nervous system of Flagellophora cf. apelti, Sterreria spp. and Nemertoderma cf. westbladi has been investigated by immunohistochemistry and confocal microscopy using anti-tubulin, anti-5-HT and anti-FMRFamide antibodies. The nervous system of F. cf. apelti is composed of a large neuropile and a loose brain at the level of the statocysts with several nerve fibres surrounding them and innervating the broom organ. Sterreria spp. shows a commissural-like brain and several neurite bundles going frontad and caudad from this. At the level of the statocysts there is also a thicker aggregation of immunoreactive fibres. The nervous system of N. cf. westbladi consists of a nerve ring lying outside the body wall musculature at the level of the statocyst and a pair of ventro-lateral neurite bundles, from which extend thinner fibres innervating the ventral side of the animal. Numerous bottle-shaped glands were observed, innervated by fibres starting both from the brain and the neurite bundles. The nervous system of the nemertodermatids studied to date displays no common pattern; instead, there is considerable plasticity in the general morphology of the nervous system. In addition, the musculature of Sterreria spp. has been studied by phalloidin staining. It shows diagonal muscles in the anterior quarter of the body and a simple orthogonal grid in the posterior three quarters, being simpler than that of the other nemertodermatids. High-resolution differential interference contrast microscopy permitted to better visualize some morphological characters of the species studied, such as statocysts, sperm and glands and, in combination with anti-tubulin staining, describe in detail the broom organ in F. cf. apelti. Finally, we note an apparent absence of innervation of the gut in Nemertodermatida similar to the condition in Xenoturbella.

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Evolution of the nervous system in Paraphanostoma (Acoela)

Cited by 58 publications

References 30 publications

The nervous system of Xenacoelomorpha: a genomic perspective

The nervous system of Xenacoelomorpha: a genomic perspective

Acoel development supports a simple planula-like urbilaterian

The plastic nervous system of Nemertodermatida

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