Publications

The mammalian vomeronasal organ (VNO), a part of the olfactory system, detects pheromones--chemical signals that modulate social and reproductive behaviours. But the molecular receptors in the VNO that detect these chemosensory stimuli remain undefined. Candidate pheromone receptors are encoded by two distinct and complex superfamilies of genes, V1r and V2r (refs 3 and 4), which code for receptors with seven transmembrane domains. These genes are selectively expressed in sensory neurons of the VNO. However, there is at present no functional evidence for a role of these genes in pheromone responses. Here, using chromosome engineering technology, we delete in the germ line of mice an approximately 600-kilobase genomic region that contains a cluster of 16 intact V1r genes. These genes comprise two of the 12 described V1r gene families, and represent approximately 12% of the V1r repertoire. The mutant mice display deficits in a subset of VNO-dependent behaviours: the expression of male sexual behaviour and maternal aggression is substantially altered. Electrophysiologically, the epithelium of the VNO of such mice does not respond detectably to specific pheromonal ligands. The behavioural impairment and chemosensory deficit support a role of V1r receptors as pheromone receptors.

The origin of eusociality in haplo-diploid organisms such as Hymenoptera has been mostly explained by kin selection. However, several studies have uncovered decreased relatedness values within colonies, resulting primarily from multiple queen matings (polyandry) and/or from the presence of more than one functional queen (polygyny). Here, we report on the use of microsatellite data for the investigation of sociogenetic parameters, such as relatedness, and levels of polygyny and polyandry, in the ant Pheidole pallidula. We demonstrate, through analysis of mother-offspring combinations and the use of direct sperm typing, that each queen is inseminated by a single male. The inbreeding coefficient within colonies and the levels of relatedness between the queens and their mate are not significantly different from zero, indicating that matings occur between unrelated individuals. Analyses of worker genotypes demonstrate that 38% of the colonies are polygynous with 2-4 functional queens, and suggest the existence of reproductive skew, i.e. unequal respective contribution of queens to reproduction. Finally, our analyses indicate that colonies are genetically differentiated and form a population exhibiting significant isolation-by-distance, suggesting that some colonies originate through budding.

Mammalian circadian rhythms are generated by a feedback loop in which BMAL1 and CLOCK, players of the positive limb, activate transcription of the cryptochrome and period genes, components of the negative limb. Bmal1 and Per transcription cycles display nearly opposite phases and are thus governed by different mechanisms. Here, we identify the orphan nuclear receptor REV-ERBalpha as the major regulator of cyclic Bmal1 transcription. Circadian Rev-erbalpha expression is controlled by components of the general feedback loop. Thus, REV-ERBalpha constitutes a molecular link through which components of the negative limb drive antiphasic expression of components of the positive limb. While REV-ERBalpha influences the period length and affects the phase-shifting properties of the clock, it is not required for circadian rhythm generation.

Large phylogeny estimation is a combinatorial optimization problem that no future computer will ever be able to solve exactly in practical computing time. The difficulty of the problem is amplified by the need to use complex evolutionary models and large taxon samplings. Hence, many heuristic approaches have been developed, with varying degrees of success. Here, we report on a heuristic approach, the metapopulation genetic algorithm, involving several populations of trees that are forced to cooperate in the search for the optimal tree. Within each population, trees are subjected to evaluation, selection, and mutation events, which are directed by using inter-population consensus information. The method proves to be both very accurate and vastly faster than existing heuristics, such that data sets comprised of hundreds of taxa can be analyzed in practical computing times under complex models of maximum-likelihood evolution. Branch support values produced by the metapopulation genetic algorithm might closely approximate the posterior probabilities of the corresponding branches.

The Su(var)3-7 gene, a haplo-suppressor and triplo-enhancer of position-effect variegation (PEV), encodes a zinc finger heterochromatin-associated protein. To understand the role of this protein in heterochromatin and genomic silencing, mutations were generated by homologous recombination. The donor fragment contained a yellow(+) gene and 7.6 kb of the Su(var)3-7 gene inserted between two FRTs. The Su(var)3-7 sequence contained three stop codons flanking an I-SceI cut site located in the 5' half of the gene. Using two different screening approaches, we obtained an allelic series composed of three mutant alleles. The three mutations are dominant suppressors of PEV. One behaves as a null mutation and results in a maternal-effect recessive lethal phenotype that can be rescued by a zygotic paternal wild-type gene. A P transposon zygotically expressing a Su(var)3-7 full-length cDNA also rescues the mutant phenotype. One hypomorphic allele is viable and the pleiotropic phenotype showed by adult flies indicates that rapidly and late dividing cells seem the most affected by reduced amounts of Su(var)3-7 protein. All three mutants were characterized at the molecular level. Each expresses a portion of the Su(var)3-7 protein that is unable to enter the nucleus and bind chromatin.

A new genus and new species of an ichthyodectiform fish, a new species of the pachyrizodontid Goulmimichthys, as well as specimens of Araripichthys sp. are described from the Agua Nueva Formation (Turonian) of Vallecillo, State of Nuevo León, NE Mexico. The ichthyodectiform fish shows a combination of characters from different families, warranting the creation of a new genus and questioning the monophyly of these families. We report herein the first record of Goulmimichthys and Araripichthys in North America.

Complete sexual development is not easily amenable to experimentation in hydra. Therefore, the analysis of gene function and gene regulation requires the introduction of exogenous DNA in a large number of cells of the hydra polyps and the significant expression of reporter constructs in these cells. We present here the procedure whereby we coupled DNA injection into the gastric cavity to electroporation of the whole animal in order to efficiently transfect hydra polyps. We could detect GFP fluorescence in both endodermal and ectodermal cell layers of live animals and in epithelial as well as interstitial cell types of dissociated hydra. In addition, we could confirm GFP protein expression by showing colocalisation between GFP fluorescence and anti-GFP immunofluorescence. Finally, when a FLAG epitope was inserted in-frame with the GFP coding sequence, GFP fluorescence also colocalised with anti-FLAG immunofluorescence. This GFP expression in hydra cells was directed by various promoters, either homologous, like the hydra homeobox cnox-2 gene promoter, or heterologous, like the two nematode ribosomal protein S5 and L28 gene promoters, and the chicken beta-actin gene promoter. This strategy provides new tools for dissecting developmental molecular mechanisms in hydra; more specifically, the genetic regulations that take place in endodermal cells at the time budding or regeneration is initiated.

The mammalian olfactory system consists of two anatomically segregated structures, the main olfactory system and the vomeronasal system, which each detect distinct types of chemical stimuli in the environment. During development, sensory neurons establish precise axonal connections with their respective targets within the olfactory bulb. The specificity of the odorant or vomeronasal receptor expressed by the sensory neuron is crucial in this process, yet it is less clear which of the more conventional axon guidance molecules are involved. Here, we show that neuropilin-2, a coreceptor for some of the class 3 semaphorins, is expressed in subpopulations of olfactory and vomeronasal sensory neurons. We generated a knock-out mutation in the neuropilin-2 gene by gene targeting in embryonic stem cells. Neuropilin-2 mutant mice exhibit profound and distinct effects on target innervation within the olfactory bulb. In the main olfactory system, axons of olfactory sensory neurons penetrate into the deeper layers of the main olfactory bulb. In the vomeronasal system, axonal fasciculation within the vomeronasal nerve is affected; some axons are misrouted and innervate glomeruli in an ectopic domain of the accessory olfactory bulb.