The nervous system of Convolutriloba (Acoela) and its patterning during regeneration after asexual reproduction

Gaerber, Christian W.; Salvenmoser, Willi; Rieger, Reinhard M.; Gschwentner, Robert

doi:10.1007/s00435-007-0039-z

Cited by 24 publications

(32 citation statements)

References 22 publications

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“…In its overall arrangement, the regularly spaced and highly concentrated array of diverse sensory cells at the front end of the planula is reminiscent of the sensory neuronal arrays of simple bilaterians (Raikova et al, 1998;Gaerber et al, 2007;Kotikova and Raikova, 2008;Schmidt-Rhaesa, 2009). Moreover, the ordered array of neural processes in this plexus has morphological features that are also found in the central neuropiles of bilaterian ganglia (Meinertzhagen, 2010).…”

Section: Evolutionary Considerationsmentioning

confidence: 98%

Complex neural architecture in the diploblastic larva of Clava multicornis (Hydrozoa, Cnidaria)

Piraino

Zega

Benedetto

et al. 2011

J of Comparative Neurology

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The organization of the cnidarian nervous system has been widely documented in polyps and medusae, but little is known about the nervous system of planula larvae, which give rise to adult forms after settling and metamorphosis. We describe histological and cytological features of the nervous system in planulae of the hydrozoan Clava multicornis. These planulae do not swim freely in the water column but rather crawl on the substrate by means of directional, coordinated ciliary movement coupled to lateral muscular bending movements associated with positive phototaxis. Histological analysis shows pronounced anteroposterior regionalization of the planula's nervous system, with different neural cell types highly concentrated at the anterior pole. Transmission electron microscopy of planulae shows the nervous system to be unusually complex, with a large, orderly array of sensory cells at the anterior pole. In the anterior half of the planula, the basiectodermal plexus of neurites forms an extensive orthogonal network, whereas more posteriorly neurites extend longitudinally along the body axis. Additional levels of nervous system complexity are uncovered by neuropeptide-specific immunocytochemistry, which reveals distinct neural subsets having specific molecular phenotypes. Together these observations imply that the nervous system of the planula of Clava multicornis manifests a remarkable level of histological, cytological, and functional organization, the features of which may be reminiscent of those present in early bilaterian animals.

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Section: Evolutionary Considerationsmentioning

confidence: 98%

Complex neural architecture in the diploblastic larva of Clava multicornis (Hydrozoa, Cnidaria)

Piraino

Zega

Benedetto

et al. 2011

J of Comparative Neurology

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“…As in C. hastifera, nervous system regeneration occurs largely by extensions of preexisting nervous system components ( Fig. 6) (Gaerber et al 2007). As longitudinal fission is progressing from anterior to posterior, the two lateral nerve cord fragments extend anteriorly and medially (Fig.…”

Section: Asexual Reproductionmentioning

confidence: 99%

Radical modification of the A–P axis and the evolution of asexual reproduction in Convolutriloba acoels

Sikes

Bely

2008

Evolution and Development

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Acoel worms in the genus Convolutriloba are remarkable in that closely related, morphologically very similar species reproduce asexually by dramatically different processes. Transverse fission, longitudinal fission, and reversed-polarity budding all occur within this genus, indicating an unparalleled ability to alter the A-P axis. Convolutriloba thus offers an exceptional opportunity to investigate the development and evolution of asexual reproduction. Molecular phylogenetic analysis indicates that reversed-polarity budding is ancestral and fission is derived for the genus. A clear difference between budding and fission is indicated by the development of the nervous system, which forms de novo during budding, but regenerates largely by extensions of remaining components of the nervous system during both types of fission. Despite this and other differences between fission and budding, localized muscle disorganization coupled with behaviorally mediated tearing are characteristic of both transverse fission and reversed-polarity budding (though not longitudinal fission), suggesting that a homologous tissue-separation mechanism underlies these two outwardly quite different asexual reproductive modes. We suggest that the ability to split the posterior axis field into two adjacent fields, manifested during both reversed-polarity budding and longitudinal fission, may have been a driving force behind the diversification of asexual reproductive mode in this group.

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“…Species on which the most work has been conducted are the convolutids Convolutriloba longifissura [8,18-22] and Symsagittifera roscoffensis [10,12,23-25] and the isodiametrid Isodiametra pulchra [26,27]. The latter lives in marine mud flats in Maine (USA) and measures about 1 mm in length.…”

Section: Introductionmentioning

confidence: 99%

The nervous system of Isodiametra pulchra (Acoela) with a discussion on the neuroanatomy of the Xenacoelomorpha and its evolutionary implications

Achatz

Martinez

2012

Front Zool

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IntroductionAcoels are microscopic marine worms that have become the focus of renewed debate and research due to their placement at the base of the Bilateria by molecular phylogenies. To date, Isodiametra pulchra is the most promising “model acoel” as it can be cultured and gene knockdown can be performed with double-stranded RNA. Despite its well-known morphology data on the nervous system are scarce. Therefore we examined this organ using various microscopic techniques, including histology, conventional histochemistry, electron microscopy, and immunocytochemistry in combination with CLSM and discuss our results in light of recently established phylogenies.ResultsThe nervous system of Isodiametra pulchra consists of a bilobed brain with a dorsal posterior commissure, a frontal ring and tracts, four pairs of longitudinal neurite bundles, as well as a supramuscular and submuscular plexus. Serotonin-like immunoreactivity (SLI) is displayed in parts of the brain, the longitudinal neurite bundles and a large part of the supramuscular plexus, while FMRFamide-like immunoreactivity (RFLI) is displayed in parts of the brain and a distinct set of neurons, the longitudinal neurite bundles and the submuscular plexus. Despite this overlap SLI and RFLI are never colocalized. Most remarkable though is the presence of a distinct functional neuro-muscular system consisting of the statocyst, tracts, motor neurons and inner muscles, as well as the presence of various muscles that differ with regard to their ultrastructure and innervation.ConclusionsThe nervous system of Isodiametra pulchra consists of an insunk, bilobed brain, a peripheral part for perception and innervation of the smooth body-wall musculature as well as tracts and motor neurons that together with pseudostriated inner muscles are responsible for steering and quick movements. The insunk, bilobed brains with two to three commissures found in numerous acoels are homologous and evolved from a ring-commissural brain that was present in the stem species of acoelomorphs. The acoelomorph brain is bipartite, consisting of a Six3/6-dependend animal pole nervous system that persists throughout adulthood and an axial nervous system that does not develop by exhibiting a staggered pattern of conserved regulatory genes as in other bilaterians but by a nested pattern of these genes. This indicates that acoelomorphs stem from an ancestor with a simple brain or with a biphasic life cycle.

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The nervous system of Convolutriloba (Acoela) and its patterning during regeneration after asexual reproduction

Cited by 24 publications

References 22 publications

Complex neural architecture in the diploblastic larva of Clava multicornis (Hydrozoa, Cnidaria)

Complex neural architecture in the diploblastic larva of Clava multicornis (Hydrozoa, Cnidaria)

Radical modification of the A–P axis and the evolution of asexual reproduction in Convolutriloba acoels

The nervous system of Isodiametra pulchra (Acoela) with a discussion on the neuroanatomy of the Xenacoelomorpha and its evolutionary implications

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