Conservation, loss, and redeployment of Wnt ligands in protostomes: implications for understanding the evolution of segment formation.

Background: The Wnt genes encode secreted glycoprotein ligands that regulate a wide range of developmental processes, including axis elongation and segmentation. There are thirteen subfamilies of Wnt genes in metazoans and this gene diversity appeared early in animal evolution. The loss of Wnt subfamilies appears to be common in insects, but little is known about the Wnt repertoire in other arthropods, and moreover the expression and function of these genes have only been investigated in a few protostomes outside the relatively Wnt-poor model species Drosophila melanogaster and Caenorhabditis elegans.

Hedgehog signaling regulates segment formation in the annelid Platynereis.

Annelids and arthropods share a similar segmented organization of the body whose evolutionary origin remains unclear. The Hedgehog signaling pathway, prominent in arthropod embryonic segment patterning, has not been shown to have a similar function outside arthropods. We show that the ligand Hedgehog, the receptor Patched, and the transcription factor Gli are all expressed in striped patterns before the morphological appearance of segments in the annelid Platynereis dumerilii.

Orthologs of key vertebrate neural genes are expressed during neurogenesis in the annelid Platynereis dumerilii.

The molecular mechanisms underlying the formation and patterning of the nervous system are relatively poorly understood for lophotrochozoans (like annelids) as compared with ecdysozoans (especially Drosophila) and deuterostomes (especially vertebrates). Therefore, we have undertaken a candidate gene approach to study aspects of neurogenesis in a polychaete annelid Platynereis dumerilii. We determined the spatiotemporal expression for Platynereis orthologs of four genes (SoxB, Churchill, prospero/Prox, and SoxC) known to play key roles in vertebrate neurogenesis.

Insights into the evolution of the snail superfamily from metazoan wide molecular phylogenies and expression data in annelids.

Background: An important issue concerning the evolution of duplicated genes is to understand why paralogous genes are retained in a genome even though the most likely fate for a redundant duplicated gene is nonfunctionalization and thereby its elimination. Here we study a complex superfamily generated by gene duplications, the snail related genes that play key roles during animal development. We investigate the evolutionary history of these genes by genomic, phylogenetic, and expression data studies.

atonal- and achaete-scute-related genes in the annelid Platynereis dumerilii: insights into the evolution of neural basic-Helix-Loop-Helix genes.

Background: Functional studies in model organisms, such as vertebrates and Drosophila, have shown that basic Helix-loop-Helix (bHLH) proteins have important roles in different steps of neurogenesis, from the acquisition of neural fate to the differentiation into specific neural cell types. However, these studies highlighted many differences in the expression and function of orthologous bHLH proteins during neural development between vertebrates and Drosophila. To understand how the functions of neural bHLH genes have evolved among bilaterians, we have performed a detailed study of bHLH genes during nervous system development in the polychaete annelid, Platynereis dumerilii, an organism which is evolutionary distant from both Drosophila and vertebrates.

Complementary striped expression patterns of NK homeobox genes during segment formation in the annelid Platynereis.

NK genes are related pan-metazoan homeobox genes. In the fruitfly, NK genes are clustered and involved in patterning various mesodermal derivatives during embryogenesis. It was therefore suggested that the NK cluster emerged in evolution as an ancestral mesodermal patterning cluster.

The expression of a hunchback ortholog in the polychaete annelid Platynereis dumerilii suggests an ancestral role in mesoderm development and neurogenesis.

Orthologs of the Drosophila gap gene hunchback have been isolated so far only in protostomes. Phylogenetic analysis of recently available genomic data allowed us to confirm that hunchback genes are widely found in protostomes (both lophotrochozoans and ecdysozoans). In contrast, no unequivocal hunchback gene can be found in the genomes of deuterostomes and non-bilaterians.

Expression of a SoxB and a Wnt2/13 gene during the development of the mollusc Patella vulgata.

We cloned and analysed the expression of a SoxB gene ( PvuSoxB) in the marine mollusc, Patella vulgata. Like its orthologues in deuterostomes, after an early broad ectodermal distribution, PvuSoxB expression only persists in cells competent to form neural structures. In the post-gastrulation larva, PvuSoxB is expressed in the prospective neuroectoderm in the head and in the trunk.

A group II intron has invaded the genus Azotobacter and is inserted within the termination codon of the essential groEL gene.

A group II intron that was previously identified within Azotobacter vinelandii by polymerase chain reac-tion with consensus primers has been completely sequenced, together with its flanking exons. In contrast to other bacterial members of group II, which are associated with mobile or other presumably non-essential DNA, the A. vinelandii intron is inserted within the termination codon of the groEL coding sequence, which it changes from UAA to UAG.

The expression of a caudal homologue in a mollusc, Patella vulgata.

We cloned and analyzed the expression of a caudal homologue (PvuCdx) during the early development of the marine gastropod, Patella vulgata. PvuCdx is expressed at the onset of gastrulation in the ectodermal cells that constitute the posterior edge of the blastopore, as well as in the paired mesentoblasts, the stem cells that generate the posterior mesoderm of the trochophore larva. During larval stages, PvuCdx is expressed in the posterior neurectoderm of the larva, as well as in part of the mesoderm.

Expression patterns of fork head and goosecoid homologues in the mollusc Patella vulgata supports the ancestry of the anterior mesendoderm across Bilateria.

We have characterised orthologues of the genes fork head and goosecoid in the gastropod Patella vulgata. In this species, the anterior-posterior (AP) axis is determined just before gastrulation, and leads to the specification of two mesodermal components on each side of the presumptive endoderm, one anterior (ectomesoderm), and one posterior (endomesoderm). Both fork head and goosecoid are expressed from the time the AP axis is specified, up to the end of gastrulation.

Yeast Pab1 interacts with Rna15 and participates in the control of the poly(A) tail length in vitro.

In Saccharomyces cerevisiae, the single poly(A) binding protein, Pab1, is the major ribonucleoprotein associated with the poly(A) tails of mRNAs in both the nucleus and the cytoplasm. We found that Pab1 interacts with Rna15 in two-hybrid assays and in coimmunoprecipitation experiments. Overexpression of PAB1 partially but specifically suppressed the rna15-2 mutation in vivo.

Multiple group II self-splicing introns in mobile DNA from Escherichia coli.

By PCR (polymerase chain reaction) amplification and cloning, we have identified four group II self-splicing introns encoding proteins related to reverse transcriptases in natural Escherichia coli isolates belonging to the ECOR collection. One intron, IntD, interrupts a DNA sequence virtually identical to that of the previously described IS3411 Insertion Sequence. A second intron, IntC, is located within an open reading frame that is closely related to a reading frame in the T-DNA of Agrobacterium tumefaciens.

Organization of the yeast URA2 gene: identification of a defective dihydroorotase-like domain in the multifunctional carbamoylphosphate synthetase-aspartate transcarbamylase complex.

The 6636 bp of the yeast URA2 gene encoding the carbamoylphosphate synthetase-aspartate transcarbamylase complex have been sequenced. The protein is organized into four regions, three of which are functional domains as indicated previously by genetic analysis. The fourth domain corresponds to a defective dihydroorotase called DHOase-like.

The primary structure of the aspartate transcarbamylase region of the URA2 gene product in Saccharomyces cerevisiae. Features involved in activity and nuclear localization.

The yeast URA2 locus encodes a multifunctional protein which possesses the carbamylphosphate synthetase and aspartate transcarbamylase activities and which catalyzes the first two reactions of the pyrimidine pathway. We report here the nucleotide sequence of the central and the 3' region of this locus. The latter encodes that part of the multifunctional protein which has the aspartate transcarbamylase activity.