2008-02-26T14:01:43+01:00
<p><img src="/system/illustrations/0000/0063/Cell1996_xsmall.jpg" alt="Cell1996.jpg_xsmall" title="Cell1996.jpg_xsmall" width="150" height="195" style="float: left;" /></p>
<p>We are interested in the regulatory mechanisms underlying vertebrate pattern formation, in both developmental and evolutionary contexts. For the past years, we have focused on Hox genes, a family of transcription factors that display special paradigmatic values, regarding their regulatory strategies, their functional organization and their key roles in morphological evolution. In the course of the past 8 years, we initiated a large program aimed at genetically dissecting these various aspects of Hox gene biology, either using the potential of established mouse genetic manipulations, or by designing and implementing a powerful strategy relying upon inter chromosomal meiotic recombination (TAMERE) or large chromosomal modifications (STRING).</p>
<p>Currently, a major effort is concentrated on the regulation of Hox gene expression. The past years of work have allowed us to produce the tools necessary to finally evaluate the function of these genes in a variety of developmental contexts. Experiments are also planed to investigate the potential function of this gene family in the course of our morphological evolution.</p>
<h3>Regulation of Hox gene expression </h3>
<ol>
<li>We pursue our efforts to understand the mechanistic basis of colinearity, i.e. the mechanism by which neighboring Hox genes are activated one after the other in overlapping anterior to posterior domains, in the trunk, and proximal to distal domains, in the limbs. The nature of this process is still elusive (even though our systematic approach has started to provide a conceptual framework, at least in limbs) and represents one of the key challenges for our laboratory. The analysis of the many lines of mice either already produced, or in the course of generation, should allow us to bring a definitive answer to this question.</li>
<li>We plan to characterize in details global regulatory controls which were shown to direct expression of groups of genes (shared enhancers) in a variety of structures such as the digits, the external genitalia, the intestinal hernia, the whisker pads or the emerging somites. These enhancer elements are of critical mechanistic and evolutionary importance and will be sought using both a genetic approach in vivo and a large-scale transgenic program using bacterial artificial chromosomes (BACs) tagged with a reporter transposon.</li>
<li>We will design a system of "Hox cluster replacement" whereby given BACs will be used as shuttle to replace the endogenous HoxD cluster in ES cells. Successful replacement will be then introduced in vivo. This methodology (perhaps applicable straight in vivo) should be very helpful to introduce a foreign cluster at the position of HoxD, to modify at will a given cluster by ET recombination of the target BAC in bacteria, or to reconstruct a "minimal Hox cluster"to better study regulatory mechanisms.<img src="/system/illustrations/0000/0068/G_D2000_xsmall.jpg" alt="G_D2000.jpg_xsmall" title="G_D2000.jpg_xsmall" width="150" height="194" style="float: right;" /></li>
</ol>
<h3>The function of Homeobox genes</h3>
<p>In parallel, we continue our attempts to unravel the functions of Hox genes by using a series of tools we have constructed over the past years. Because of both the large redundancy observed in this gene family, and compensatory mechanisms, multiple and conditional gene knock-out will be necessary to precisely evaluate the function of these genes.</p>
<ol>
<li>Conditional gene inactivations will be carried out using the cre/loxP system, primarily on the entire HoxA cluster. This is necessary as the inactivations of at least Hoxa13 and Hoxa1 proved to be lethal.</li>
<li>Various combinations of Hoxd gene gain of function and loss of function produced as a result of our TAMERE approach are currently being evaluated. Preliminary results, as well as a first set of data obtained in limbs, demonstrate the strong potential of- and validate this approach.</li>
<li>Gene profiling analyses will be carried out using the Affymetrix system, to look for target genes of the Hox gene network in well-defined situations, i.e. by using some of our engineered configurations. In particular, target will be looked for in relation to inter-digital spacing, as well as in the context of the ontogenetic relationships between the digits and the external genitalia.</li>
</ol>
<h3><img src="/system/illustrations/0000/0073/Nature2002_xsmall.jpg" alt="Nature2002.jpg_xsmall" title="Nature2002.jpg_xsmall" width="150" height="198" style="float: left;" />Evolutionary approaches</h3>
<p>We also continue to explore the involvement of Hox genes in morphological evolution, at the levels of both the modification of regulatory controls, and the resulting variations in the functional deployment of HOX proteins and their impacts upon the emergence of novel structures in the course of vertebrate phylogeny. In relation to this problem, molecular and functional analyses of DNA sequences highly conserved between various taxa are being carried out.</p>
<p> </p>
<p><img src="/system/illustrations/0000/0063/Cell1996_xsmall.jpg" alt="Cell1996.jpg_xsmall" title="Cell1996.jpg_xsmall" width="150" height="195" style="float: left;" /></p>
<p>We are interested in the regulatory mechanisms underlying vertebrate pattern formation, in both developmental and evolutionary contexts. For the past years, we have focused on Hox genes, a family of transcription factors that display special paradigmatic values, regarding their regulatory strategies, their functional organization and their key roles in morphological evolution. In the course of the past 8 years, we initiated a large program aimed at genetically dissecting these various aspects of Hox gene biology, either using the potential of established mouse genetic manipulations, or by designing and implementing a powerful strategy relying upon inter chromosomal meiotic recombination (TAMERE) or large chromosomal modifications (STRING).</p>
<p>Currently, a major effort is concentrated on the regulation of Hox gene expression. The past years of work have allowed us to produce the tools necessary to finally evaluate the function of these genes in a variety of developmental contexts. Experiments are also planed to investigate the potential function of this gene family in the course of our morphological evolution.</p>
<h3>Regulation of Hox gene expression </h3>
<ol>
<li>We pursue our efforts to understand the mechanistic basis of colinearity, i.e. the mechanism by which neighboring Hox genes are activated one after the other in overlapping anterior to posterior domains, in the trunk, and proximal to distal domains, in the limbs. The nature of this process is still elusive (even though our systematic approach has started to provide a conceptual framework, at least in limbs) and represents one of the key challenges for our laboratory. The analysis of the many lines of mice either already produced, or in the course of generation, should allow us to bring a definitive answer to this question.</li>
<li>We plan to characterize in details global regulatory controls which were shown to direct expression of groups of genes (shared enhancers) in a variety of structures such as the digits, the external genitalia, the intestinal hernia, the whisker pads or the emerging somites. These enhancer elements are of critical mechanistic and evolutionary importance and will be sought using both a genetic approach in vivo and a large-scale transgenic program using bacterial artificial chromosomes (BACs) tagged with a reporter transposon.</li>
<li>We will design a system of "Hox cluster replacement" whereby given BACs will be used as shuttle to replace the endogenous HoxD cluster in ES cells. Successful replacement will be then introduced in vivo. This methodology (perhaps applicable straight in vivo) should be very helpful to introduce a foreign cluster at the position of HoxD, to modify at will a given cluster by ET recombination of the target BAC in bacteria, or to reconstruct a "minimal Hox cluster"to better study regulatory mechanisms.<img src="/system/illustrations/0000/0068/G_D2000_xsmall.jpg" alt="G_D2000.jpg_xsmall" title="G_D2000.jpg_xsmall" width="150" height="194" style="float: right;" /></li>
</ol>
<h3>The function of Homeobox genes</h3>
<p>In parallel, we continue our attempts to unravel the functions of Hox genes by using a series of tools we have constructed over the past years. Because of both the large redundancy observed in this gene family, and compensatory mechanisms, multiple and conditional gene knock-out will be necessary to precisely evaluate the function of these genes.</p>
<ol>
<li>Conditional gene inactivations will be carried out using the cre/loxP system, primarily on the entire HoxA cluster. This is necessary as the inactivations of at least Hoxa13 and Hoxa1 proved to be lethal.</li>
<li>Various combinations of Hoxd gene gain of function and loss of function produced as a result of our TAMERE approach are currently being evaluated. Preliminary results, as well as a first set of data obtained in limbs, demonstrate the strong potential of- and validate this approach.</li>
<li>Gene profiling analyses will be carried out using the Affymetrix system, to look for target genes of the Hox gene network in well-defined situations, i.e. by using some of our engineered configurations. In particular, target will be looked for in relation to inter-digital spacing, as well as in the context of the ontogenetic relationships between the digits and the external genitalia.</li>
</ol>
<h3><img src="/system/illustrations/0000/0073/Nature2002_xsmall.jpg" alt="Nature2002.jpg_xsmall" title="Nature2002.jpg_xsmall" width="150" height="198" style="float: left;" />Evolutionary approaches</h3>
<p>We also continue to explore the involvement of Hox genes in morphological evolution, at the levels of both the modification of regulatory controls, and the resulting variations in the functional deployment of HOX proteins and their impacts upon the emergence of novel structures in the course of vertebrate phylogeny. In relation to this problem, molecular and functional analyses of DNA sequences highly conserved between various taxa are being carried out.</p>
1
Homeobox containing genes and the molecular biology of vertebrate development
Homeobox containing genes and the molecular biology of vertebrate development
17
Vertebrate development
2009-05-08T15:58:08+02:00