Biomedical subjects

Francine Boucher

Publications and source records attributed to Francine Boucher.

4 recordsLinked to original sources

PubMed2006

Laminar organization of the early developing anterior hypothalamus.

The bHLH-PAS transcription factor SIM1 is required for the development of neurons of the anterior hypothalamus (AH). In order to dissect this developmental program, we compared gene expression in the AH of E12.5 Sim1(+/+) and Sim1(-/-) littermates using an oligonucleotide-based microarray. Our analysis identified 48 genes that were downregulated and 8 genes that were upregulated. We examined the expression pattern of 10 of the identified genes--Cart, Cbln1, Alcam, Unc-13c, Rgs4, Lnx4, Irx3, Sax1, Ldb2 and Neurod6--by in situ hybridization in E12.5 embryos. All of these genes are expressed in domains that are contained within that of Sim1 and their expression is changed in Sim1(-/-) embryos as predicted by the microarray analysis. Classical dating studies have established that the hypothalamus follows an "outside-in" pattern of neurogenesis, with neurons of the lateral hypothalamus being born before the medial ones. Analysis of the genes identified in this microarray study showed that the developing AH is characterized by different layers of gene expression that most likely correspond to distinct waves of neurogenesis. In addition, our analysis suggests that Sim1 function is required for the production or the survival of postmitotic neurons as well as for correct positioning of AH neurons.

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PubMed2005

Sim1 and Sim2 are required for the correct targeting of mammillary body axons.

The mammillary body (MB), and its axonal projections to the thalamus (mammillothalamic tract, MTT) and the tegmentum (mammillotegmental tract, MTEG), are components of a circuit involved in spatial learning. The bHLH-PAS transcription factors SIM1 and SIM2 are co-expressed in the developing MB. We have found that MB neurons are generated and that they survive at least until E18.5 in embryos lacking both Sim1 and Sim2 (Sim1(-/-);Sim2(-/-)). However, the MTT and MTEG are histologically absent in Sim1(-/-);Sim2(-/-) embryos, and are reduced in embryos lacking Sim1 but bearing one or two copies of Sim2, indicating a contribution of the latter to the development of MB axons. We have generated, by homologous recombination, a null allele of Sim1 (Sim1(tlz)) in which the tau-lacZ fusion gene was introduced, allowing the staining of MB axons. Consistent with the histological studies, lacZ staining showed that the MTT/MTEG is barely detectable in Sim1(tlz/tlz);Sim2(+/-) and Sim1(tlz/tlz);Sim2(-/-) brains. Instead, MB axons are splayed and grow towards the midline. Slit1 and Slit2, which code for secreted molecules that induce the repulsion of ROBO1-producing axons, are expressed in the midline at the level of the MB, whereas Robo1 is expressed in the developing MB. The expression of Rig-1/Robo3, a negative regulator of Slit signalling, is upregulated in the prospective MB of Sim1/Sim2 double mutants, raising the possibility that the growth of mutant MB axons towards the midline is caused by a decreased sensitivity to SLIT. Finally, we found that Sim1 and Sim2 act along compensatory, but not hierarchical, pathways, suggesting that they play similar roles in vivo.

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PubMed2005

Looking for trouble: a search for developmental defects of the hypothalamus.

The hypothalamus is a critical integrator of several homeostatic processes that are required for the survival of vertebrates. Disruption of the development of the hypothalamus thus has the potential of perturbing important physiological processes with lifelong consequences. We review current knowledge about how cell types are specified and circuits are formed within the developing hypothalamus. We emphasize the potential clinical impact of the perturbations of these pathways using the regulation of energy balance as a model. We predict that disruption of hypothalamic development is a common, previously unsuspected cause of disorders of homeostatic processes such as obesity and high blood pressure.

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PubMed2003

Regulatory interaction between arylhydrocarbon receptor and SIM1, two basic helix-loop-helix PAS proteins involved in the control of food intake.

The basic helix-loop-helix PAS (bHLH-PAS) transcription factors SIM1 and arylhydrocarbon receptor (AHR) are involved in the control of feeding behavior. Sim1 haploinsufficiency causes hyperphagia in mice and humans, most likely by perturbing the hypothalamus function. The administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a ligand of AHR, causes severe anorexia, which also appears to be of central origin. Both SIM1 and AHR require heterodimerization either with ARNT or ARNT2 to function. Here, we characterize the promoter for Sim1 and show that a consensus AHR-ARNT/2 binding site positively regulates its activity in the context of transfection experiments in Neuro-2A cells. A gel shift assay indicated that AHR-ARNT/2 can bind its putative site in the Sim1 promoter. Overexpression of Arnt, Arnt2, or Ahr increased the activity of a reporter construct containing the Sim1 promoter by 1.8-, 1.5-, and 2.2-fold, respectively, but failed to do so when the AHR-ARNT/2 binding site was mutated. Similarly, TCDD increased the activity of the reporter construct by 1.8-fold but not that of its mutated version. Finally, we found that TCDD increased Sim1 expression in Neuro-2A cells and in mouse kidney and hypothalamus by 4-, 3-, and 2-fold, respectively. We conclude that Sim1 expression is regulated by AHR-ARNT/2. This result raises the possibility that Sim1 mediates the effect of TCDD on feeding and points to a complex network of regulatory interactions between bHLH-PAS proteins.

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