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Fate and nature of the onychophoran mouth-anus furrow and its contribution to the blastopore.

ABSTRACT: The ancestral states of bilaterian development, and which living groups have conserved them the most, has been a controversial topic in biology for well over a hundred years. In recent years, the idea that gastrulation primitively proceeded via the formation of a slit-like blastopore that then evolved into either protostomy or deuterostomy has gained renewed attention and some molecular developmental support. One of the key pieces of evidence for this 'amphistomy' theory comes from the onychophorans, which form a clear ventral groove during gastrulation. The interpretation of this structure has, however, proved problematic. Based on expression patterns of forkhead (fkh), caudal (cad), brachyury (bra) and wingless (wg/Wnt1), we show that this groove does not correspond to the blastopore, even though both the mouth and anus later develop from it. Rather, the posterior pit appears to be the blastopore; the posterior of the groove later fuses with it to form the definitive anus. Onychophoran development therefore represents a case of 'concealed' deuterostomy. The new data from the onychophorans thus remove one of the key pieces of evidence for the amphistomy theory. Rather, in line with other recent results, it suggests that ancestral bilaterian development was deuterostomic.

SUBMITTER: Janssen R

PROVIDER: S-EPMC4389607 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Fate and nature of the onychophoran mouth-anus furrow and its contribution to the blastopore.

Janssen Ralf R Jörgensen Mette M Lagebro Linda L Budd Graham E GE

Proceedings. Biological sciences 20150401 1805

The ancestral states of bilaterian development, and which living groups have conserved them the most, has been a controversial topic in biology for well over a hundred years. In recent years, the idea that gastrulation primitively proceeded via the formation of a slit-like blastopore that then evolved into either protostomy or deuterostomy has gained renewed attention and some molecular developmental support. One of the key pieces of evidence for this 'amphistomy' theory comes from the onychopho ...[more]

PMID: 25788603

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Project description:Viral RNA-dependent RNA polymerases (RdRps) are major determinants of high mutation rates and generation of mutant spectra that mediate RNA virus adaptability. The RdRp of the picornavirus foot-and-mouth disease virus (FMDV), termed 3D, is a multifunctional protein that includes a nuclear localization signal (NLS) in its N-terminal region. Previous studies documented that some amino acid substitutions within the NLS altered nucleotide recognition and enhanced the incorporation of the mutagenic purine analogue ribavirin in viral RNA, but the mutants tested were not viable and their response to lethal mutagenesis could not be studied. Here we demonstrate that NLS amino acid substitution M16A of FMDV serotype C does not affect infectious virus production but accelerates ribavirin-mediated virus extinction. The mutant 3D displays polymerase activity, RNA binding, and copying processivity that are similar to those of the wild-type enzyme but shows increased ribavirin-triphosphate incorporation. Crystal structures of the mutant 3D in the apo and RNA-bound forms reveal an expansion of the template entry channel due to the replacement of the bulky Met by Ala. This is a major difference with other 3D mutants with altered nucleotide analogue recognition. Remarkably, two distinct loop ?9-?11 conformations distinguish 3Ds that exhibit higher or lower ribavirin incorporation than the wild-type enzyme. This difference identifies a specific molecular determinant of ribavirin sensitivity of FMDV. Comparison of several polymerase mutants indicates that different domains of the molecule can modify nucleotide recognition and response to lethal mutagenesis. The connection of this observation with current views on quasispecies adaptability is discussed.IMPORTANCE The nuclear localization signal (NLS) of the foot-and-mouth disease virus (FMDV) polymerase includes residues that modulate the sensitivity to mutagenic agents. Here we have described a viable NLS mutant with an amino acid replacement that facilitates virus extinction by ribavirin. The corresponding polymerase shows increased incorporation of ribavirin triphosphate and local structural modifications that implicate the template entry channel. Specifically, comparison of the structures of ribavirin-sensitive and ribavirin-resistant FMDV polymerases has identified loop ?9-?11 conformation as a determinant of sensitivity to ribavirin mutagenesis.

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Fate and nature of the onychophoran mouth-anus furrow and its contribution to the blastopore.

Publications

Fate and nature of the onychophoran mouth-anus furrow and its contribution to the blastopore.

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