Evolutionary biology. Small but mighty timekeepers.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
A Adoutte
Publications and source records attributed to A Adoutte.
The new animal phylogeny: reliability and implications.
DNA sequence analysis dictates new interpretation of phylogenic trees. Taxa that were once thought to represent successive grades of complexity at the base of the metazoan tree are being displaced to much higher positions inside the tree. This leaves no evolutionary "intermediates" and forces us to rethink the genesis of bilaterian complexity.
Animals↗
Genomes and evolution. Editorial overview
Explore the source record for details and available documents.
Journal Article↗
Hox genes in brachiopods and priapulids and protostome evolution.
Understanding the early evolution of animal body plans requires knowledge both of metazoan phylogeny and of the genetic and developmental changes involved in the emergence of particular forms. Recent 18S ribosomal RNA phylogenies suggest a three-branched tree for the Bilateria comprising the deuterostomes and two great protostome clades, the lophotrochozoans and ecdysozoans. Here, we show that the complement of Hox genes in critical protostome phyla reflects these phylogenetic relationships and reveals the early evolution of developmental regulatory potential in bilaterians. We have identified Hox genes that are shared by subsets of protostome phyla. These include a diverged pair of posterior (Abdominal-B-like) genes in both a brachiopod and a polychaete annelid, which supports the lophotrochozoan assemblage, and a distinct posterior Hox gene shared by a priapulid, a nematode and the arthropods, which supports the ecdysozoan clade. The ancestors of each of these two major protostome lineages had a minimum of eight to ten Hox genes. The major period of Hox gene expansion and diversification thus occurred before the radiation of each of the three great bilaterian clades.
Amino Acid Sequence↗
Animal evolution. The end of the intermediate taxa?
Contrary to general belief, there has not been a reliable, global phylogeny of animals at hand within the past few decades. Recent progress in molecular phylogeny is rapidly changing the situation and has provided trees that constitute a reference frame for discussing the still controversial evolution of body plans. These trees, once purged of their possible artefacts, have already yielded confirmation of traditional, anatomically based, phylogenies as well as several new and quite significant results. Of these, one of the most striking is the disappearance of two superphyla (acoelomates such as flatworms, pseudocoelomates such as nematodes) previously thought to represent grades of intermediate complexity between diploblasts (organisms with two germ layers) and triploblasts (organisms with three germ layers). The overall image now emerging is of a fairly simple global tree of metazoans, comprising only a small number of major branches. The topology nicely accounts for the striking conservation of developmental genes in all bilaterians and suggests a new interpretation of the 'Cambrian explosion' of animal diversity.
Animal Population Groups↗
Purification, in vitro reassembly, and preliminary sequence analysis of epiplasmins, the major constituent of the membrane skeleton of Paramecium.
The epiplasmic layer, a continuous rigid granulo-fibrillar sheet directly subtending the surface membranes of Paramecium, is one of the outermost of the various cytoskeletal networks that compose it cortex. We have previously shown that the epiplasm consists of a set of 30 to 50 protein bands on SDS-PAGE in the range 50 to 33 kDa, the epiplasmins. We report a purification procedure for the set of epiplasmic proteins, a description of their physicochemical and reassembly properties, and a preliminary characterization of their sequence. The conditions for solubilization of the epiplasm and for in vitro reassembly of its purified constituents ar described. Reassembly of the entire set of proteins and of some (but not all) subsets are shown to yield filamentous aggregates. Microsequences of two purified bands of epiplasmins reveal a striking amino acid sequence consisting of heptad repeats of only three main amino acids, P, V, and Q. These repeats were confirmed by DNA sequencing of polymerase chain reaction products. The motif is QPVQ-h, in which h is a hydrophobic residue. This may constitute the core of the epiplasmin sequence and, in view of the tendency of such a sequence to form a coiled-coil, may account for the remarkable self-aggregation properties of epiplasmins.
Amino Acid Sequence↗
Axonemal tubulin polyglycylation probed with two monoclonal antibodies: widespread evolutionary distribution, appearance during spermatozoan maturation and possible function in motility.
Two monoclonal antibodies, AXO 49 and TAP 952, probed with carboxy-terminal peptides from Paramecium axonemal tubulin and with polyglycylated synthetic peptides, are found to recognize differently tubulin polyglycylation, the most recently identified posttranslational modification discovered in Paramecium axonemal tubulin. With these antibodies, we show that tubulin polyglycylation is widely distributed in organisms ranging from ciliated protozoa to mammals; it arose early in the course of evolution, but seems to be absent in primitive protozoa such as the Euglenozoa. Tubulin polyglycylation is the last posttranslational modification which takes place in the course of Drosophila spermatogenesis and its occurrence corresponds to the end of spermatozoan maturation. An involvement of polyglycylated tubulin in axoneme motility is suggested since AXO 49 and TAP 952 specifically inhibit the reactivated motility of sea urchin spermatozoa.
Amino Acid Sequence↗
Genetic code deviations in the ciliates: evidence for multiple and independent events.
In several species of ciliates, the universal stop codons UAA and UAG are translated into glutamine, while in the euplotids, the glutamine codon usage is normal, but UGA appears to be translated as cysteine. Because the emerging position of this monophyletic group in the eukaryotic lineage is relatively late, this deviant genetic code represents a derived state of the universal code. The question is therefore raised as to how these changes arose within the evolutionary pathways of the phylum. Here, we have investigated the presence of stop codons in alpha tubulin and/or phosphoglycerate kinase gene coding sequences from diverse species of ciliates scattered over the phylogenetic tree constructed from 28S rRNA sequences. In our data set, when deviations occur they correspond to in frame UAA and UAG coding for glutamine. By combining these new data with those previously reported, we show that (i) utilization of UAA and UAG codons occurs to different extents between, but also within, the different classes of ciliates and (ii) the resulting phylogenetic pattern of deviations from the universal code cannot be accounted for by a scenario involving a single transition to the unusual code. Thus, contrary to expectations, deviations from the universal genetic code have arisen independently several times within the phylum.
Animals↗
Why does the genetic code deviate so easily in ciliates?
Explore the source record for details and available documents.
Animals↗
Direct visualization of a vast cortical calcium compartment in Paramecium by secondary ion mass spectrometry (SIMS) microscopy: possible involvement in exocytosis.
The plasma membrane of ciliates is underlaid by a vast continuous array of membrane vesicles known as cortical alveoli. Previous work had shown that a purified fraction of these vesicles actively pumps calcium, suggesting that alveoli may constitute a calcium-storage compartment. Here we provide direct confirmation of this hypothesis using in situ visualization of total cell calcium on sections of cryofixed and cryosubstituted cells analyzed by SIMS (secondary ion mass spectrometry) microscopy a method never previously applied to protists. A narrow, continuous, Ca-emitting zone located all along the cell periphery was observed on sections including the cortex. In contrast, Na and K were evenly distributed throughout the cell. Various controls confirmed that emission was from the alveoli, in particular, the emitting zone was still seen in mutants totally lacking trichocysts, the large exocytotic organelles docked at the cell surface, indicating that they make no major direct contribution to the emission. Calcium concentration within alveoli was quantified for the first time in SIMS microscopy using an external reference and was found to be in the range of 3 to 5 mM, a value similar to that for sarcoplasmic reticulum. After massive induction of trichocyst discharge, this concentration was found to decrease by about 50%, suggesting that the alveoli are the main source of the calcium involved in exocytosis.
Animals↗
Polyglycylation of tubulin: a posttranslational modification in axonemal microtubules.
A posttranslational modification was detected in the carboxyl-terminal region of axonemal tubulin from Paramecium. Tubulin carboxyl-terminal peptides were isolated and analyzed by Edman degradation sequencing, mass spectrometry, and amino acid analysis. All of the peptides, derived from both alpha and beta tubulin subunits, were modified by polyglycylation, containing up to 34 glycyl units covalently bound to the gamma carboxyl group of glutamyl residues. This modification, present in one of the most stable microtubular systems, may influence microtubule stability or axoneme function, or both.
Amino Acid Sequence↗
Isolation and characterization of libraries of monoclonal antibodies directed against various forms of tubulin in Paramecium.
Ciliates are very good models for studying post-translationally generated tubulin heterogeneity because they exhibit highly differentiated microtubular networks in combination with reduced genetic diversity. We have approached the analysis of tubulin heterogeneity in Paramecium through extensive isolation and characterization of monoclonal antibodies using various antigens and several immunization protocols. Eight monoclonal antibodies and 10 hybridoma supernatants were characterized by: i) immunoblotting on ciliate and pig brain tubulins as well as on peptide maps of Paramecium axonemal tubulin; ii) immunoblotting on ciliate tubulin fusion peptides generated in E coli, a procedure which allows in principle to discriminate antibodies that are directed against tubulin sequence (reactive on fusion peptides) from those directed against a post-translational epitope (non-reactive); and iii) immunofluorescence on Paramecium, 3T3 and PtK2 cells. Twelve antibodies labeled all microtubules in Paramecium cells and were found to be directed against tubulin primary sequences (nine of them being located in the alpha N-terminal domain, one in the beta C-terminal one, and two in alpha and beta central stretches). The remaining ones decorated only a specific subset of microtubules within the cell and were presumably directed against post-translational modifications. Among these, three antibodies are directed against an N-terminal acetylated epitope of alpha-tubulin whereas the epitopes of three other ones (TAP 952 degrees, AXO 58 and AXO 49 degrees) apparently correspond to still unidentified post-translational modifications, located in the C-terminal domain of both alpha- and beta-tubulins. The AXO 49 degrees specificity is similar to that of a previously described polyclonal serum raised against Paramecium axonemal tubulin [2]. The results are discussed in terms of identification and accessibility of the epitopes and immunogenicity of ciliate tubulin with reference to mammalian and ciliate tubulin sequences.
Amino Acid Sequence↗
The major lines of metazoan evolution: summary of traditional evidence and lessons from ribosomal RNA sequence analysis.
Explore the source record for details and available documents.
Animals↗
A broad molecular phylogeny of ciliates: identification of major evolutionary trends and radiations within the phylum.
The cellular architecture of ciliates is one of the most complex known within eukaryotes. Detailed systematic schemes have thus been constructed through extensive comparative morphological and ultrastructural analysis of the ciliature and of its internal cytoskeletal derivatives (the infraciliature), as well as of the architecture of the oral apparatus. In recent years, a consensus was reached in which the phylum was divided in eight classes as defined by Lynn and Corliss [Lynn, D. H. & Corliss, J. O. (1991) in Microscopic Anatomy of Invertebrates: Protozoa (Wiley-Liss, New York), Vol. 1, pp. 333-467]. By comparing partial sequences of the large subunit rRNA molecule, and by using both distance-matrix and maximum-parsimony-tree construction methods (checked by boot-strapping), we examine the phylogenetic relationships of 22 species belonging to seven of these eight classes. At low taxonomic levels, the traditional grouping of the species is generally confirmed. At higher taxonomic levels, the branching pattern of these seven classes is resolved in several deeply separated major branches. Surprisingly, the first emerging one contains the heterotrichs and is strongly associated with a karyorelictid but deeply separated from hypotrichs. The litostomes, the oligohymenophorans, and the hypotrichs separate later in a bush-like topology hindering the resolution of their order of diversification. These results show a much more ancient origin of heterotrichs than was classically assumed, indicating that asymmetric, abundantly ciliated oral apparatuses do not correspond to "highly evolved" traits as previously thought. They also suggest the occurrence of a major radiative explosion in the evolutionary history of the ciliates, yielding five of the eight classes of the phylum. These classes appear to differ essentially according to the cytoskeletal architecture used to shape and sustain the cellular cortex (a process of essential adaptative and morphogenetic importance in ciliates).
Animals↗
ATP synthase subunit c/III/9 gene sequences as a tool for interkingdom and metaphytes molecular phylogenies.
The 38 sequences of the ATPase c/III/9 gene determined in bacteria, fungi, mammals, and higher plants have been used to construct phylogenetic trees by distance matrix and parsimony methods (checked by bootstrapping); alignments have been performed on the deduced amino-acid sequences and then transferred back to the nucleotide sequences. Three lineages stand out: (1) eubacteria (except cyanobacteria and alpha purple bacteria), (2) chloroplasts, together with cyanobacteria, and (3) mitochondria together with nuclei and alpha purple bacteria. The clear monophyly of the mitochondrial/nuclear lineage, taken all together, strongly suggests that the nuclear copies of the gene now residing in the eukaryotic nucleus originate from a mitochondrial transfer. Within this lineage, metaphytes emerge late and as a cohesive group, after fungi (as a dispersed group) and metazoa, yielding an order that markedly differs from that obtained through typical RNA nuclear molecules. The possible biphyletic origin of mitochondria based on mitochondrial rRNA sequences is not evidenced by these sequences. Internal branches within both the chloroplastic and the mitochondrial lineages are consistent with botanical evolutionary schemes based on morphological characters. In spite of its relatively small size, the ATPase c/III/9 gene therefore displays remarkable properties as a phylogenetic index and adds a new tool for molecular evolutionary reconstructions, especially within the metaphytes.
Amino Acid Sequence↗
An analysis of the origin of metazoans, using comparisons of partial sequences of the 28S RNA, reveals an early emergence of triploblasts.
In order to study the origin of metazoans, we have compared sequences from the 5' end of the large subunit ribosomal RNA of a number of protists, fungi, plants and metazoans, including all diploblastic phyla (sequences of 10 new species have been determined, including that of the placozoan, Trichoplax adhaerens). These sequences were analyzed using distance matrix, maximum parsimony and maximum likelihood methods, and the validity of the results was ascertained with bootstrapping and species removal or addition. Triploblasts and diploblasts formed two clearly separated monophyletic units; this divergence, which apparently preceded the diversification of diploblastic animals (i.e. the successive sponge, ctenophore, cnidarian radiations), showed a much more ancient origin of triploblasts with respect to diploblasts than classically assumed. These results do not exclude the possibility that triploblasts and diploblasts arose independently from different protists.
Animals↗
Microtubule diversity in ciliated cells: evidence for its generation by post-translational modification in the axonemes of Paramecium and quail oviduct cells.
The diversity of microtubular networks was analyzed in quail oviduct and in Paramecium cells using conventional and confocal immunofluorescence as well as pre- and post-embedding EM immunocytochemistry with a variety of anti-tubulin antibodies. The 6-11B-1 monoclonal antibody, specific for the post-translational acetylation of Lys 40 of alpha-tubulin, and a polyclonal antibody raised against Paramecium axonemal tubulin (anti-PA tubulin antibody) both decorated stable microtubular arrays in Paramecium ie ciliary axonemes and a set of microtubular bundles associated with the cortex, suggesting that the two antibodies may be directed against the same epitope. However, several differences in the immunocytological patterns yielded by each antibody on the two cell types were evident. For example, in quail, as in all other Metazoa, the anti-PA tubulin antibody only decorated axonemes enclosed in normal ciliary membrane while it was unreactive on cytoplasmic tubulins. Immunoblotting of peptide maps of axonemal tubulins demonstrated that the epitopes of the two antibodies were indeed completely different. Double immunolabelling of dividing paramecia using a universal anti-tubulin antibody and the anti-PA tubulin one revealed that all newly assembled microtubular arrays were first detected by the universal antibody and, only shortly afterwards, by the anti-PA tubulin one. This provided a strong indication that the anti-PA tubulin antibody is directed against a post-translational modification taking place on already assembled microtubules (MTs) (as previously known to be the case for acetylation and detyrosination). In taxol-treated quail cells undergoing ciliogenesis, massive assembly of MTs and even axonemes occurred in the cytoplasm. These MTs were not decorated by the anti-PA tubulin antibody however, suggesting that in Metazoa the post-translational modification can only take place within the ciliary lumen. The present work provides one further mechanism for generating MT immunological and biochemical diversity post-translationally; this may account for the high multiplicity of tubulin isoforms observed in ciliates which contain very little if any genetic diversity of tubulin genes.
Animals↗