ROLE OF HOXA2 IN MOUSE EXTERNAL EAR MORPHOGENESIS: A MODEL TO DECIPHER HUMAN CRANIOFACIAL GENETIC DISORDERS

Oral Communication presentad at the ";;Forum des Jeunes Chercheurs";; Brest (France) October 2011. Substituting abstract

Mice with targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 reveal synergistic interactions.

Journal ArticleThe Hox genes encode transcription factors which mediate the formation of the mammalian body plan along the anteroposterior and appendicular axes. Paralogous Hox genes within the separate linkage groups are closely related with respect to DNA sequence and expression, suggesting that they could have at least partially redundant functions. We showed previously that mice homozygous for independent targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 had no defects in common. But our current analysis of double mutants has revealed strong, dosage-dependent interactions between these genes. We report here that in hoxd-3- homozygotes the first cervical vertebra, the atlas, is homeotically transformed to the adjacent anterior structure. Unexpectedly, in double mutants, rather than observing a more extensive homeotic transformation, the entire atlas is deleted. These observations are interpreted in terms of a model in which these Hox genes differentially regulate the proliferation rates of the appropriate sets of precursor cells

Biomedical Discovery Acceleration, with Applications to Craniofacial Development

The profusion of high-throughput instruments and the explosion of new results in the scientific literature, particularly in molecular biomedicine, is both a blessing and a curse to the bench researcher. Even knowledgeable and experienced scientists can benefit from computational tools that help navigate this vast and rapidly evolving terrain. In this paper, we describe a novel computational approach to this challenge, a knowledge-based system that combines reading, reasoning, and reporting methods to facilitate analysis of experimental data. Reading methods extract information from external resources, either by parsing structured data or using biomedical language processing to extract information from unstructured data, and track knowledge provenance. Reasoning methods enrich the knowledge that results from reading by, for example, noting two genes that are annotated to the same ontology term or database entry. Reasoning is also used to combine all sources into a knowledge network that represents the integration of all sorts of relationships between a pair of genes, and to calculate a combined reliability score. Reporting methods combine the knowledge network with a congruent network constructed from experimental data and visualize the combined network in a tool that facilitates the knowledge-based analysis of that data. An implementation of this approach, called the Hanalyzer, is demonstrated on a large-scale gene expression array dataset relevant to craniofacial development. The use of the tool was critical in the creation of hypotheses regarding the roles of four genes never previously characterized as involved in craniofacial development; each of these hypotheses was validated by further experimental work

A Zn-finger protein, Xfin, is expressed during cone differentiation in the retina of the frog Xenopus laevis

Xfin is a member of a Zn-finger multigene family that shares homology with the Drosophila segmentation gene, Kr\ufcppel. This paper reports on our identification and cellular localization, through the utilization of specific antibodies, of the expression product of Xfin in the Xenopus laevis retina, and its pattern of expression during the retinal developmental stages. By immunostaining sections of the retina, we show that the major staining is localized in the cytoplasm of the cones. The protein appears at an early differentiation stage of the cones, when they can not be univocally identified by morphological criteria, and is maintained up to the adult retina. The same antigenicity pattern is detectable in the retina of the anuran genus Bufo. The immunostaining data are confirmed by Western blot analysis on Xenopus eye protein extracts. Because of its cytoplasmic localization, and because of the ability of Zn-finger proteins to bind nucleic acids, we think that Xfin may be involved in the terminal differentiation of the cones through RNA-protein interactions

A Xenopus multifinger protein, Xfin, is expressed in specialized cell types and is localized in the cytoplasm

Xfin is a member of a large family of Kr\ufcppel-type transcripts stored in the Xenopus egg, whose function is unknown. By using polyclonal antibodies raised against fusion proteins containing different portions of Xfin, we have identified the Xfin gene product and established its pattern of expression in some adult tissues and during oogenesis and embryogenesis. The corresponding mRNA localization has been studied by in situ hybridization on ovary and testis sections. The Xfin product is found in the cytoplasm, both during oogenesis and adulthood; in adult tissues, it is differentially expressed in a cell-type specific fashion. The expression of the protein in specialized cell types and its cytoplasmic localization may favour the hypothesis that it could be involved in cell differentiation events through protein-RNA interactions

Two dispersed highly repeated DNA families of Triturus vulgaris meridionalis (Amphibia Urodela) are widely conserved among Salamandridae

Two BamHI families of repeated sequences were characterized from the genome of the Italian smooth newt, Triturus vulgaris meridionalis (Amphibia, Urodela). The first family, which is divided into subfamilies, consists of tandemly arranged arrays whose basic repeat is around 398 bp long; these arrays are dispersed throughout the entire chromosome sets of the various species of Triturus tested. Moreover the family is widely conserved among Salamandridae, being detected by genomic DNA blotting of Notophthalmus viridescens, Taricha granulosa, Salamandrina terdigitata and Euproctus platycephalus. The second BamHI family is represented by a cloned sequence of 419 bp, which is dispersed in the chromosome set of several species of Triturus. The sequence is also conserved in S. terdigitata and in E. platycephalus but is not detectable in N. viridescens or T. granulosa. The cloned sequence is most probably only part of a longer unit interspersed within the Triturus genome

2 DISPERSED HIGHLY REPEATED DNA FAMILIES OF TRITURUS-VULGARIS-MERIDIONALIS (AMPHIBIA, URODELA) ARE WIDELY CONSERVED AMONG SALAMANDRIDAE

Two BamHI families of repeated sequences were characterized from the genome of the Italian smooth newt, Triturus vulgaris meridionalis (Amphibia, Urodela). The first family, which is divided into subfamilies, consists of tandemly arranged arrays whose basic repeat is around 398 bp long; these arrays are dispersed throughout the entire chromosome sets of the various species of Triturus tested. Moreover the family is widely conserved among Salamandridae, being detected by genomic DNA blotting of Notophthalmus viridescens, Taricha granulosa, Salamandrina terdigitata and Euproctus platycephalus. The second BamHI family is represented by a cloned sequence of 419 bp, which is dispersed in the chromosome set of several species of Triturus. The sequence is also conserved in S. terdigitata and in E. platycephalus but is not detectable in N. viridescens or T. granulosa. The cloned sequence is most probably only part of a longer unit interspersed within the Triturus genome

Integration of anteroposterior and dorsoventral regulation of Phox2b transcription in cranial motoneuron progenitors by homeodomain proteins

Little is known about the molecular mechanisms that integrate anteroposterior (AP) and dorsoventral (DV) positional information in neural progenitors that specify distinct neuronal types within the vertebrate neural tube. We have previously shown that in ventral rhombomere (r)4 of Hoxb1 and Hoxb2 mutant mouse embryos, Phox2b expression is not properly maintained in the visceral motoneuron progenitor domain (pMNv), resulting in a switch to serotonergic fate. Here, we show that Phox2b is a direct target of Hoxb1 and Hoxb2. We found a highly conserved Phox2b proximal enhancer that mediates rhombomere-restricted expression and contains separate Pbx-Hox (PH) and Prep/Meis (P/M) binding sites. We further show that both the PH and P/M sites are essential for Hox-Pbx-Prep ternary complex formation and regulation of the Phox2b enhancer activity in ventral r4. Moreover, the DV factor Nkx2.2 enhances Hox-mediated transactivation via a derepression. mechanism. Finally, we show that induction of ectopic Phox2b-expressing visceral motoneurons in the chick hindbrain requires the combined activities of Hox and Nkx2 homeodomain proteins. This study takes an important first step to understand how activators and repressors, induced along the AP and DV axes in response to signaling pathways, interact to regulate specific target gene promoters, leading to neuronal fate specification in the appropriate developmental context