1,721,056 research outputs found
Hox and ParaHox genes in bivalves molluscs.
No full textIn this study, we sought the presence and analysed the sequences of the Hox and ParaHox genes in bivalve molluscs. The clustered Hox genes play a central role in anterior-posterior axial patterning in bilaterian metazoa, whereas the ParaHox gene cluster is a paralogue (evolutionary sister) of the Hox cluster. Using polymerase chain reaction (PCR)-based approaches, we isolated nine different sequences in five species belonging to three of the main bivalve subclasses: Ensis ensis and Tapes philippinarum (Heterodonta), Pecten maximus and Mytilus galloprovincialis (Pteriomorphia), and Yoldia eightsi (Protobranchia). Comparison with the Hox and ParaHox genes of other bilaterians, particularly lophotrochozoans, allowed us to attribute six of these sequences to the Hox gene cluster (one to paralog group [PG] 3 class, and five to the central class), two to the ParaHox cluster and one to the Gbx gene family. The results of our investigation seem to indicate that homeotic Hox and ParaHox gene clusters are homogeneous for both presence and characteristics in molluscs. © 2003 Elsevier B.V. All rights reserved
Hox genes in the Antarctic polyplacophoran Nuttallochiton mirandus.
No full textABSTRACT Hox genes are conserved across all bilaterians and encode transcription factors
involved in the formation of the anteroposterior axis during embryo development. Differences in
homeotic gene evolution have been observed not only between deuterostomes and protostomes, but
also between the two large protostome clades, Ecdysozoa and Lophotrochozoa.
Among lophotrochozoans, the phylum Mollusca displays high diversity of body plans, ranging from
the wormlike appearance of aplacophorans to the complex body plan of cephalopods. Using a PCRbased
method, we were able to identify eight Hox genes in the polyplacophoran Nuttallochiton
mirandus, two orthologous to the anterior class (lab, pb), four to the central class (Scr, Lox5, Antp,
Lox2) and two to the posterior class (Post-1, Post-2). Comparison with the results obtained in other
molluscs seems to confirm the conservation of Hox genes in this phylum in terms of both presence
and characteristics
Transposable elements in vertebrates: species evolution and environmental adaptation.
No full textThe evolutionary success of species is strictly related to their genome in terms of composition and functionality. Transposable elements (TEs) represent a considerable fraction of the nuclear DNA content, and given to their ability to spread throughout the genome, they are able to create genetic diversity at sequence, gene structure, and chromosome level. Vertebrates represent a highly successful taxon and its lineages are characterized by a variable TE content suggesting a different impact on the genome. In this manuscript, we highlight the importance of TEs in creating new regulatory sequences and genetic innovations extremely useful for diversification of vertebrates. Moreover, an increasing number of evidence suggests a link between TEs and environment. Indeed, given the richness of species adapted to a wide range of habitats and conditions, vertebrates are exposed to several ecological pressures with consequent effects on evolutionary adaptation
Molecular data from the 16S rRNA gene for the phylogeny of Pectinidae (Mollusca: Bivalvia).
No full textMolecular phylogeny of the family Pectinidae (Mollusca: Bivalvia) based on mitochondrial 16S and 12S rRNA genes.
No full textAbstract:
Pectinidae is a large bivalve family characterised by almost circular, flat shells. Species are distributed worldwide and fall into three life-styles: swimming, byssally attached to hard substrates, and cemented to rocks with one valve. Despite these very different life strategies, pectinid shells are highly conservative in shape and offer few clues for the unravelling of phylogenetic issues. Consequently, phylogenetic studies based on morphological features have not yielded conclusive results. We thus set out to analyse partial sequences of mitochondrial 12S and 16S rRNA genes from 23 species of 16 genera with molecular techniques. The results are largely in contrast, both at the genus and the subfamily level, with the systematic classifications based on adult morphological characters, whereas they agree with the morphological classifications based on the more conserved non-adaptive features
Taxonomic consideration on the Antarctic species Adamussium colbecki based on molecular data
No full textComparative analysis of the karyology of some Antarctic and Mediterranean Perciform fish species
No full textPhylogenetic relationships within the Ovulidae (Gastropoda: Cypraeoidea) based on 16S rRNA sequences
No full textClosely interacting groups, such as hosts and parasites, sometimes provide useful models to study evolution and adaptive processes. In Ovulidae, a widespread family of specialised browsing carnivorous molluscs that feed on polyps and tissues of Anthozoa, close association with the host has produced a plethora of adaptations affecting shell morphology, colour pattern and mantle shape. These morphological characters have been widely used in ovulid taxonomy, although putative differences are often based on trivial and inconsistent variations. In this work we used a molecular approach to generate the basal phylogeny of the family. Phylogenetic analyses of mitochondrial 16S rRNA gene sequences of 32 species from 23 genera reveal unexpected taxonomic groupings from the genus up to the family level, as well as unexpected phenomena of homoplasy in conchological features. Since molecular phylogenies also provide an evolutionary framework where character transformations are polarised, we used this basal ovulid phylogeny to explore the specificity of the association and the degree of morphological adaptation to the hos
Phylogenetic relationships within Ovulidae (Gastropoda: Cypraeoidea) based on molecular data from the 16S rRNA gene.
No full textAbstract: Closely interacting groups, such as hosts and parasites, sometimes provide useful models to study
evolution and adaptive processes. In Ovulidae, a widespread family of specialised browsing carnivorous molluscs that feed on polyps and tissues of Anthozoa, close association with the host has produced a plethora of adaptations affecting shell morphology, colour pattern and mantle shape. These morphological characters have been widely used in ovulid taxonomy, although putative differences are often based on trivial and inconsistent variations. In this work we used a molecular approach to generate the basal phylogeny of the family. Phylogenetic analyses of mitochondrial 16S rRNA gene sequences of 32 species from 23 genera reveal unexpected taxonomic groupings from the genus up to the family level, as well as unexpected phenomena of homoplasy in conchological features. Since molecular phylogenies also
provide an evolutionary framework where character transformations are polarised, we used this basal ovulid
phylogeny to explore the specificity of the association and the degree of morphological adaptation to the hos
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