Cellular dynamics of host - parasitoid interactions: Insights from the encapsulation process in a partially resistant host.

Cotesia typhae is an eastern African endoparasitoid braconid wasp that targets the larval stage of the lepidopteran stem borer, Sesamia nonagrioides, a maize crop pest in Europe. The French host population is partially resistant to the Makindu strain of the wasp, allowing its development in only 40% of the cases. Resistant larvae can encapsulate the parasitoid and survive the infection.

Interference with the retinoic acid signalling pathway inhibits the initiation of teeth and caudal primary scales in the small-spotted catshark .

The retinoic acid (RA) pathway was shown to be important for tooth development in mammals, and suspected to play a key role in tooth evolution in teleosts. The general modalities of development of tooth and "tooth-like" structures (collectively named odontodes) seem to be conserved among all jawed vertebrates, both with regard to histogenesis and genetic regulation. We investigated the putative function of RA signalling in tooth and scale initiation in a cartilaginous fish, the small-spotted catshark .

Molecular footprinting of skeletal tissues in the catshark Scyliorhinus canicula and the clawed frog Xenopus tropicalis identifies conserved and derived features of vertebrate calcification.

Understanding the evolutionary emergence and subsequent diversification of the vertebrate skeleton requires a comprehensive view of the diverse skeletal cell types found in distinct developmental contexts, tissues, and species. To date, our knowledge of the molecular nature of the shark calcified extracellular matrix, and its relationships with osteichthyan skeletal tissues, remain scarce. Here, based on specific combinations of expression patterns of the Col1a1, Col1a2, and Col2a1 fibrillar collagen genes, we compare the molecular footprint of endoskeletal elements from the chondrichthyan Scyliorhinus canicula and the tetrapod Xenopus tropicalis.

Altered retinoic acid signalling underpins dentition evolution.

Small variations in signalling pathways have been linked to phenotypic diversity and speciation. In vertebrates, teeth represent a reservoir of adaptive morphological structures that are prone to evolutionary change. Cyprinid fish display an impressive diversity in tooth number, but the signals that generate such diversity are unknown.

Heterogeneous conservation of Dlx paralog co-expression in jawed vertebrates.

Background: The Dlx gene family encodes transcription factors involved in the development of a wide variety of morphological innovations that first evolved at the origins of vertebrates or of the jawed vertebrates. This gene family expanded with the two rounds of genome duplications that occurred before jawed vertebrates diversified. It includes at least three bigene pairs sharing conserved regulatory sequences in tetrapods and teleost fish, but has been only partially characterized in chondrichthyans, the third major group of jawed vertebrates.

Pattern and polarity in the development and evolution of the gnathostome jaw: both conservation and heterotopy in the branchial arches of the shark, Scyliorhinus canicula.

The acquisition of jaws constitutes a landmark event in vertebrate evolution, one that in large part potentiated their success and diversification. Jaw development and patterning involves an intricate spatiotemporal series of reciprocal inductive and responsive interactions between the cephalic epithelia and the cranial neural crest (CNC) and cephalic mesodermal mesenchyme. The coordinated regulation of these interactions is critical for both the ontogenetic registration of the jaws and the evolutionary elaboration of variable jaw morphologies and designs.

The homology of odontodes in gnathostomes: insights from Dlx gene expression in the dogfish, Scyliorhinus canicula.

Background: Teeth and tooth-like structures, together named odontodes, are repeated organs thought to share a common evolutionary origin. These structures can be found in gnathostomes at different locations along the body: oral teeth in the jaws, teeth and denticles in the oral-pharyngeal cavity, and dermal denticles on elasmobranch skin. We, and other colleagues, had previously shown that teeth in any location were serially homologous because: i) pharyngeal and oral teeth develop through a common developmental module; and ii) the expression patterns of the Dlx genes during odontogenesis were highly divergent between species but almost identical between oral and pharyngeal dentitions within the same species.

Evolution of repeated structures along the body axis of jawed vertebrates, insights from the Scyliorhinus canicula Hox code.

The Hox gene family encodes homeodomain-containing transcription factors involved in the patterning of structures composed of repeated elements along the antero-posterior axis of Bilateralia embryos. In vertebrate, Hox genes are thought to control the segmental identity of the rhombomeres, the branchial arches, and the somites. They are therefore thought to have played a key role in the morphological evolution of structures like the jaw, girdles, and vertebrae in gnathostomes.

Development of oral and pharyngeal teeth in the medaka (Oryzias latipes): comparison of morphology and expression of eve1 gene.

Gnathostome teeth are one of the most promising models for developmental evolutionary studies, they are the most abundant organ in the fossil record and an excellent example of organogenesis. Teeth have a complex morphology and are restricted to the mouth in mammals, whereas actinopterygian teeth have a simple morphology and are found in several locations, notably on pharyngeal bones. Morphological and developmental similarities support the hypothesis that oral and pharyngeal teeth are serially homologous.

Posterior hoxa genes expression during zebrafish bony fin ray development and regeneration suggests their involvement in scleroblast differentiation.

Expression of two zebrafish developmental posterior hoxa genes, hoxa11b and hoxa13b, was studied by in situ hybridization during pectoral and caudal fin development and regeneration. Expression was restricted to cells of the bony rays region. During fin development, molecular cytological analysis revealed that a subpopulation of mesenchymal cells expressed these two hoxa genes during their early differentiation in the subapical region of the developing ray.

Comparison of even-skipped related gene expression pattern in vertebrates shows an association between expression domain loss and modification of selective constraints on sequences.

The even-skipped related genes (evx) encode homeodomain-containing transcription factors that play key roles in body patterning and neurogenesis in a wide array of Eumetazoa species. It is thought that the genome of the last common ancestor of Chordata contained a unique evx gene linked to a unique ancestral Hox complex. During subsequent evolution, two rounds of whole genome duplication followed by individual gene losses gave rise to three paralogs: evx1, evx2, and eve1.