Animal Evolution: A Soap Opera of Unremarkable Worms

Lowe, Christopher J.; Pani, Ariel M.

doi:10.1016/j.cub.2010.12.017

Cited by 11 publications

(9 citation statements)

References 15 publications

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“…Likewise, within the Chordata, TnI isoforms in vertebrates and urochordates branched after these groups split, suggesting that these isoforms are derived from a single common ancestor rather than multiple isoform‐specific ancestors. Although phylogenetic positioning of the acoel flatworm (Xenacoelomorpha) is still under debate [Egger et al, ; Lowe and Pani, ], our unbiased analysis suggests that TnI from Symsagittifera (acoel flatworms) is an early branch within the Deuterostomia TnI group (Fig. ), which agrees with the placement based on extensive molecular phylogenetic analysis [Philippe et al, ].…”

Section: Phylogenetic Relationships Of Troponin I Sequences Suggest Tsupporting

confidence: 87%

Molecular evolution of troponin I and a role of its N‐terminal extension in nematode locomotion

et al. 2016

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Summary The troponin complex, composed of troponin T (TnT), troponin I (TnI), and troponin C (TnC), is the major calcium-dependent regulator of muscle contraction, which is present widely in both vertebrates and invertebrates. Little is known about evolutionary aspects of troponin in the animal kingdom. Using a combination of data mining and functional analysis of TnI, we report evidence that an N-terminal extension of TnI is present in most of bilaterian animals as a functionally important domain. Troponin components have been reported in species in most of representative bilaterian phyla. Comparison of TnI sequences shows that the core domains are conserved in all examined TnIs, and that N- and C-terminal extensions are variable among isoforms and species. In particular, N-terminal extensions are present in all protostome TnIs and chordate cardiac TnIs but lost in a subset of chordate TnIs including vertebrate skeletal-muscle isoforms. Transgenic rescue experiments in C. elegans striated muscle show that the N-terminal extension of TnI (UNC-27) is required for coordinated worm locomotion but not in sarcomere assembly and single muscle-contractility kinetics. These results suggest that N-terminal extensions of TnIs are retained from a TnI ancestor as a functional domain.

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Section: Phylogenetic Relationships Of Troponin I Sequences Suggest Tsupporting

confidence: 87%

Molecular evolution of troponin I and a role of its N‐terminal extension in nematode locomotion

et al. 2016

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“…Nowhere is this more evident than in the xenoturbellids (and acoelomorph flatworms) which now appear to be massively simplified deuterostomes (now comprising the Xenocoelomorpha) and the sister group to the ambulacrarians [46]. As such they are uninformative as to either the appearance of the most primitive deuterostomes (let alone bilaterians [47]) or by implication the putative position of the vetulicolians.…”

Section: Discussionmentioning

confidence: 99%

Evidence for gill slits and a pharynx in Cambrian vetulicolians: implications for the early evolution of deuterostomes

Morris

Han

et al. 2012

BMC Biol

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BackgroundVetulicolians are a group of Cambrian metazoans whose distinctive bodyplan continues to present a major phylogenetic challenge. Thus, we see vetulicolians assigned to groups as disparate as deuterostomes and ecdysozoans. This divergence of opinions revolves around a strikingly arthropod-like body, but one that also bears complex lateral structures on its anterior section interpreted as pharyngeal openings. Establishing the homology of these structures is central to resolving where vetulicolians sit in metazoan phylogeny.ResultsNew material from the Chengjiang Lagerstätte helps to resolve this issue. Here, we demonstrate that these controversial structures comprise grooves with a series of openings. The latter are oval in shape and associated with a complex anatomy consistent with control of their opening and closure. Remains of what we interpret to be a musculature, combined with the capacity for the grooves to contract, indicate vetulicolians possessed a pumping mechanism that could process considerable volumes of seawater. Our observations suggest that food captured in the anterior cavity was transported to dorsal and ventral gutters, which then channeled material to the intestine. This arrangement appears to find no counterpart in any known fossil or extant arthropod (or any other ecdysozoan). Anterior lateral perforations, however, are diagnostic of deuterostomes.ConclusionsIf the evidence is against vetulicolians belonging to one or other group of ecdysozoan, then two phylogenetic options seem to remain. The first is that such features as vetulicolians possess are indicative of either a position among the bilaterians or deuterostomes but apart from the observation that they themselves form a distinctive and recognizable clade current evidence can permit no greater precision as to their phylogenetic placement. We argue that this is too pessimistic a view, and conclude that evidence points towards vetulicolians being members of the stem-group deuterostomes; a group best known as the chordates (amphioxus, tunicates, vertebrates), but also including the ambulacrarians (echinoderms, hemichordates), and xenoturbellids. If the latter, first they demonstrate that these members of the stem group show few similarities to the descendant crown group representatives. Second, of the key innovations that underpinned deuterostome success, the earliest and arguably most seminal was the evolution of openings that define the pharyngeal gill slits of hemichordates (and some extinct echinoderms) and chordates.

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“…The sister clade of Chordata, the Ambulacraria, comprises hemichordates plus echinoderms. The enigmatic, possibly primitive, possibly highly reduced, worm-like bilaterian Xenoturbella will not be further considered here, as its phylogenetic position as a basal deuterostome remains too controversial [20-22], and has recently been rigorously challenged [23]. …”

Section: Introductionmentioning

confidence: 99%

How Hox genes can shed light on the place of echinoderms among the deuterostomes

David

Mooi

2014

EvoDevo

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BackgroundThe Hox gene cluster ranks among the greatest of biological discoveries of the past 30 years. Morphogenetic patterning genes are remarkable for the systems they regulate during major ontogenetic events, and for their expressions of molecular, temporal, and spatial colinearity. Recent descriptions of exceptions to these colinearities are suggesting deep phylogenetic signal that can be used to explore origins of entire deuterostome phyla. Among the most enigmatic of these deuterostomes in terms of unique body patterning are the echinoderms. However, there remains no overall synthesis of the correlation between this signal and the variations observable in the presence/absence and expression patterns of Hox genes.ResultsRecent data from Hox cluster analyses shed light on how the bizarre shift from bilateral larvae to radial adults during echinoderm ontogeny can be accomplished by equally radical modifications within the Hox cluster. In order to explore this more fully, a compilation of observations on the genetic patterns among deuterostomes is integrated with the body patterning trajectories seen across the deuterostome clade.ConclusionsSynthesis of available data helps to explain morphogenesis along the anterior/posterior axis of echinoderms, delineating the origins and fate of that axis during ontogeny. From this, it is easy to distinguish between ‘seriality’ along echinoderm rays and true A/P axis phenomena such as colinearity within the somatocoels, and the ontogenetic outcomes of the unique translocation and inversion of the anterior Hox class found within the Echinodermata. An up-to-date summary and integration of the disparate lines of research so far produced on the relationship between Hox genes and pattern formation for all deuterostomes allows for development of a phylogeny and scenario for the evolution of deuterostomes in general, and the Echinodermata in particular.

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Animal Evolution: A Soap Opera of Unremarkable Worms

Cited by 11 publications

References 15 publications

Molecular evolution of troponin I and a role of its N‐terminal extension in nematode locomotion

Molecular evolution of troponin I and a role of its N‐terminal extension in nematode locomotion

Evidence for gill slits and a pharynx in Cambrian vetulicolians: implications for the early evolution of deuterostomes

How Hox genes can shed light on the place of echinoderms among the deuterostomes

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