Zakany J, Duboule D

National Research Centre "Frontiers in Genetics," Department of Genetics and Evolution, University of Geneva, 1211 Geneva 4, Switzerland.

Although neural substrates of mammalian female mating behavior have been described [1, 2], the association between complex courtship activity and specific underlying mechanisms remains elusive [3]. We have isolated a mouse line that unexpectedly shows altered female social behavior with increased investigation of males and increased genital biting. We investigated adult individuals by behavioral observation and genetic and molecular neuroanatomy methods. We report exacerbated inverse pursuits and incapacitating bites directed at the genitals of stud males. This extreme deviation from wild-type female courtship segregates with a deletion of the Hoxd1 to Hoxd9 genomic region. This dominant Atypical female courtship allele (HoxD(Afc)) induces ectopic Hoxd10 gene expression in several regions in newborn forebrain transitorily and stably in a sparse subpopulation of cells in the cornu ammonis fields of adult hippocampus, which may thus lead to an abnormal modulation in the sexual behavior of mutant females. The resulting compulsive sexual solicitation behavior displayed by the most affected individuals suggests new avenues to study the genetic and molecular bases of normal and pathological mammalian affect and raises the potential involvement of the hippocampus in the control of female courtship behavior. The potential relevance to human 2q.31.1 microdeletion syndrome [4, 5] is discussed.

Delpretti S, Zakany J, Duboule D

National Research Centre "Frontiers in Genetics," School of Life Sciences, Ecole Polytechnique Federale, Lausanne, Switzerland.

Background: Four posterior Hoxd genes, from Hoxd13 to Hoxd10, are collectively regulated during the development of tetrapod digits. Besides the well-documented role of Hoxd13, the function of the neighboring genes has been difficult to evaluate due to the close genetic linkage and potential regulatory interferences. We used a combination of five small nested deletions in cis, involving from two to four consecutive genes of the Hoxd13 to Hoxd9 loci, in mice, to evaluate their combined functional importance. Results: We show that deletions leading to a gain of function of Hoxd13, via regulatory re-allocation, generate abnormal phenotypes, in agreement with the dominant negative role of this gene. We also show that Hoxd10, Hoxd11, and Hoxd12 all seem to play a genuine role in digit development, though less compelling than that of Hoxd13. In contrast, the nearby Hoxd9 contributed no measurable function in digits. Conclusions: We conclude that a slight and transient deregulation of Hoxd13 expression can readily affect the relative lengths of limb segments and that all posterior Hoxd genes likely contribute to the final limb morphology. We discuss the difficulty to clearly assess the functional share of individual genes within such a gene family, where closely located neighbors, coding for homologous proteins, are regulated by a unique circuitry and all contribute to shape the distal parts of our appendages. Developmental Dynamics, 2012. (c) 2012 Wiley Periodicals, Inc.

Friedli M, Barde I, Arcangeli M, Verp S, Quazzola A, Zakany J, Lin-Marq N, Robyr D, Attanasio C, Spitz F, Duboule D, Trono D, Antonarakis S E

Department of Genetic Medicine and Development, University of Geneva Medical School and University Hospitals of Geneva, Geneva, Switzerland.

Finding sequences that control expression of genes is central to understanding genome function. Previous studies have used evolutionary conservation as an indicator of regulatory potential. Here, we present a method for the unbiased in vivo screen of putative enhancers in large DNA regions, using the mouse as a model. We cloned a library of 142 overlapping fragments from a 200 kb-long murine BAC in a lentiviral vector expressing LacZ from a minimal promoter, and used the resulting vectors to infect fertilized murine oocytes. LacZ staining of E11 embryos obtained by first using the vectors in pools and then testing individual candidates led to the identification of 3 enhancers, only one of which shows significant evolutionary conservation. In situ hybridization and 3C/4C experiments suggest that this enhancer, which is active in the neural tube and posterior diencephalon, influences the expression of the Olig1 and/or Olig2 genes. This work provides a new approach for the large-scale in vivo screening of transcriptional regulatory sequences, and further demonstrates that evolutionary conservation alone seems too limiting a criterion for the identification of enhancers.

Tschopp P, Tarchini B, Spitz F, Zakany J, Duboule D

Department of Zoology and Animal Biology, National Research Centre Frontiers in Genetics, University of Geneva, Sciences III, Geneva, Switzerland.

During development of the vertebrate body axis, Hox genes are transcribed sequentially, in both time and space, following their relative positions within their genomic clusters. Analyses of animal genomes support the idea that Hox gene clustering is essential for coordinating the various times of gene activations. However, the eventual collinear ordering of the gene specific transcript domains in space does not always require genomic clustering. We analyzed these complex regulatory relationships by using mutant alleles at the mouse HoxD locus, including one that splits the cluster into two pieces. We show that both positive and negative regulatory influences, located on either side of the cluster, control an early phase of collinear expression in the trunk. Interestingly, this early phase does not systematically impact upon the subsequent expression patterns along the main body axis, indicating that the mechanism underlying temporal collinearity is distinct from those acting during the second phase. We discuss the potential functions and evolutionary origins of these mechanisms, as well as their relationship with similar processes at work during limb development.

Di-Poi N, Zakany J, Duboule D

Department of Zoology and Animal Biology, University of Geneva, Geneva, Swizerland.

Hox genes encode homeodomain-containing proteins that control embryonic development in multiple contexts. Up to 30 Hox genes, distributed among all four clusters, are expressed during mammalian kidney morphogenesis, but functional redundancy between them has made a detailed functional account difficult to achieve. We have investigated the role of the HoxD cluster through comparative molecular embryological analysis of a set of mouse strains carrying targeted genomic rearrangements such as deletions, duplications, and inversions. This analysis allowed us to uncover and genetically dissect the complex role of the HoxD cluster. Regulation of metanephric mesenchyme-ureteric bud interactions and maintenance of structural integrity of tubular epithelia are differentially controlled by some Hoxd genes during renal development, consistent with their specific expression profiles. We also provide evidence for a kidney-specific form of colinearity that underlies the differential expression of two distinct sets of genes located on both sides and overlapping at the Hoxd9 locus. These insights further our knowledge of the genetic control of kidney morphogenesis and may contribute to understanding certain congenital kidney malformations, including polycystic kidney disease and renal hypoplasia.

Zacchetti G, Duboule D, Zakany J

National Research Centre 'Frontiers in Genetics', Department of Zoology and Animal Biology, University of Geneva, Sciences III, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland.

The digestive tract is made of different subdivisions with various functions. During embryonic development, the developing intestine expresses combinations of Hox genes along its anterior to posterior axis, suggesting a role for these genes in this regionalization process. In particular, the transition from small to large intestine is labelled by the transcription of all Hoxd genes except Hoxd12 and Hoxd13, the latter two genes being transcribed only near the anus. Here, we describe two lines of mice that express Hoxd12 ectopically within this morphological transition. As a consequence, budding of the caecum is impeded, leading to complete agenesis in homozygous individuals. This effect is concurrent with a dramatic reduction of both Fgf10 and Pitx1 expression. Furthermore, the interactions between ;anterior' Hox genes and ectopic Hoxd12 suggest a model whereby anterior and posterior Hox products compete in controlling Fgf10 signalling, which is required for the growth of this organ in mice. These results illuminate components of the genetic cascade necessary for the emergence of this gut segment, crucial for many vertebrates.

Zakany J, Duboule D

National Research Centre Frontiers in Genetics, Department of Zoology and Animal Biology, University of Geneva, Sciences III, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland. jozsef.zakany@zoo...

The potential role of Hox genes during vertebrate limb development was brought into focus by gene expression analyses in mice (P Dolle, JC Izpisua-Belmonte, H Falkenstein, A Renucci, D Duboule, Nature 1989, 342:767-772), at a time when limb growth and patterning were thought to depend upon two distinct and rather independent systems of coordinates; one for the anterior-to-posterior axis and the other for the proximal-to-distal axis (see D Duboule, P Dolle, EMBO J 1989, 8:1497-1505). Over the past years, the function and regulation of these genes have been addressed using both gain-of-function and loss-of-function approaches in chick and mice. The use of multiple mutations either in cis-configuration in trans-configuration or in cis/trans configurations, has confirmed that Hox genes are essential for proper limb development, where they participate in both the growth and organization of the structures. Even though their molecular mechanisms of action remain somewhat elusive, the results of these extensive genetic analyses confirm that, during the development of the limbs, the various axes cannot be considered in isolation from each other and that a more holistic view of limb development should prevail over a simple cartesian, chess grid-like approach of these complex structures. With this in mind, the functional input of Hox genes during limb growth and development can now be re-assessed.

Zakany J, Zacchetti G, Duboule D

Department of Zoology and Animal Biology and National Research Centre/Frontiers in Genetics, University of Geneva, Sciences III, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland.

The development of the vertebrate limb is dependent upon two signaling centers, the apical ectodermal ridge (AER), which provides the underlying mesenchyme with essential growth factors, and the zone of polarizing activity (ZPA), the source of the Sonic hedgehog (SHH) product. Recent work involving gain and loss of function of Hox genes has emphasized their impact both on AER maintenance and Shh transcriptional activation. Here, we describe antagonistic interactions between posterior Hoxd genes and Gli3, suggesting that the latter product protects the AER from the deleterious effect of the formers, and we present evidence that Fgf10 is the mediator of HOX-dependent AER expansion. Furthermore, the striking similarity between some of the hereby observed Hox/Gli3-dependent morphogenetic defects and those displayed by fetuses with severely altered retinoic acid metabolism suggests a tight connection between these various pathways. The nature of these potential interactions is discussed in the context of proximal-distal growth and patterning.

Duboule D, Tarchini B, Zakany J, Kmita M

Department of Zoology and Animal Biology, University of Geneva, Sciences III, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland.

Genes belonging to both HoxA and HoxD clusters are required for proper vertebrate limb development. Mice lacking all, or parts of, Hoxa and Hoxd functions in forelimbs, as well as mice with a gain of function of these genes in the early limb bud, have helped us to understand functional and regulatory issues associated with these genes, such that, for example, the tight mechanistic interdependency that exists between the production of the limb and its anterior to posterior (AP) polarity. Our studies suggest that the evolutionary recruitment of Hox gene function into growing appendages was crucial to implement hedgehog signalling, subsequently leading to the distal extension of tetrapod appendages, with an already built-in AP polarity. We propose that this process results from the evolutionary co-option, in the developing limbs, of a particular regulatory mechanism (collinearity), which is necessary to pattern the developing trunk. This major regulatory constraint imposed a polarity to our limbs as the most parsimonious solution to grow appendages.

Kmita M, Tarchini B, Zakany J, Logan M, Tabin C J, Duboule D

Department of Zoology and Animal Biology and National Research Centre Frontiers in Genetics, University of Geneva, Sciences III, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland.

Vertebrate HoxA and HoxD cluster genes are required for proper limb development. However, early lethality, compensation and redundancy have made a full assessment of their function difficult. Here we describe mice that are lacking all Hoxa and Hoxd functions in their forelimbs. We show that such limbs are arrested early in their developmental patterning and display severe truncations of distal elements, partly owing to the absence of Sonic hedgehog expression. These results indicate that the evolutionary recruitment of Hox gene function into growing appendages might have been crucial in implementing hedgehog signalling, subsequently leading to the distal extension of tetrapod appendages. Accordingly, these mutant limbs may be reminiscent of an ancestral trunk extension, related to that proposed for arthropods.