Biomedical subjects

J Deschamps

Publications and source records attributed to J Deschamps.

At least 19 recordsLinked to original sources

PubMed2001

Axial skeletal patterning in mice lacking all paralogous group 8 Hox genes.

We present a detailed study of the genetic basis of mesodermal axial patterning by paralogous group 8 Hox genes in the mouse. The phenotype of Hoxd8 loss-of-function mutants is presented, and compared with that of Hoxb8- and Hoxc8-null mice. Our analysis of single mutants reveals common features for the Hoxc8 and Hoxd8 genes in patterning lower thoracic and lumbar vertebrae. In the Hoxb8 mutant, more anterior axial regions are affected. The three paralogous Hox genes are expressed up to similar rostral boundaries in the mesoderm, but at levels that strongly vary with the axial position. We find that the axial region affected in each of the single mutants mostly corresponds to the area with the highest level of gene expression. However, analysis of double and triple mutants reveals that lower expression of the other two paralogous genes also plays a patterning role when the mainly expressed gene is defective. We therefore conclude that paralogous group 8 Hox genes are involved in patterning quite an extensive anteroposterior (AP) axial region. Phenotypes of double and triple mutants reveal that Hoxb8, Hoxc8 and Hoxd8 have redundant functions at upper thoracic and sacral levels, including positioning of the hindlimbs. Interestingly, loss of functional Hoxb8 alleles partially rescues the phenotype of Hoxc8- and Hoxc8/Hoxd8-null mutants at lower thoracic and lumbar levels. This suggests that Hoxb8 affects patterning at these axial positions differently from the other paralogous gene products. We conclude that paralogous Hox genes can have a unique role in patterning specific axial regions in addition to their redundant function at other AP levels.

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PubMed1999

Targeted inactivation of Hoxb8 affects survival of a spinal ganglion and causes aberrant limb reflexes.

Hoxb8 mutant mice were generated by inserting the lacZ coding sequence in frame with the first exon of Hoxb8. These mice express a fusion protein with a functional beta-galactosidase activity instead of Hoxb8. Mutant embryos were analyzed for anatomical changes. The results indicate that Hoxb8 is not an indispensable regulator of A-P patterning in the forelimb, unlike suggested by our Hoxb8 gain of function experiments (Charité J, DeGraaff W, Shen S, Deschamps J. Cell 1994;78:589-601). The null mutant phenotypic traits include degeneration of the second spinal ganglion (C2), an abnormality opposite to the alteration in the gain of function transgenic mice. Subtle changes in the thoracic part of the vertebral column were observed as well. Adult homozygous mutants exhibit an abnormal clasping reflex of the limbs.

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PubMed1999

Initiation, establishment and maintenance of Hox gene expression patterns in the mouse.

Spatially and temporally restricted expression of the Hox genes along the main and appendicular axes is essential for correct patterning of vertebrate embryos. In this overview we discuss the latest data that shed light on the mechanisms underlying the generation of the expression domains of the Hox genes. The molecular genetic interactions governing initial transcription of the Hox genes in the posterior part of the primitive streak during mouse and chick gastrulation remain enigmatic. But the recent discovery by Kondo and Duboule (Cell, 97, 1999, 407-417) of a "cluster repressive regulation", will undoubtedly lead to a better understanding of the molecular genetic mechanism underlying colinear and sequential initiation of Hox gene transcription. Recently progress has been booked in characterizing the basal processes driving progression of the Hox expression domains during their establishment. Hox expression is still labile while being established. The transcriptional state of Hox genes in anterior tissues can be reprogrammed under the influence of more posterior locations. Posteriorizing activity may involve RA and FGF signaling. It is only when these interactions and, in some cases at least, regulatory interactions with Hox and cdx gene products occur appropriately, that the Hox expression domains would be correctly established. After the Hox expression domains have been established, regulatory processes involving the products of Polycomb and trithorax- Group genes start operating, perpetuating the transcriptional state of the Hox genes within and outside the expression domains. Whether control at the level of chromatin structure, believed to operate during the late maintenance phase of Hox gene expression, is also involved in regulating concerted initial expression of these genes, is a possibility that has been suggested.

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PubMed1998

Transducing positional information to the Hox genes: critical interaction of cdx gene products with position-sensitive regulatory elements.

Studies of pattern formation in the vertebrate central nervous system indicate that anteroposterior positional information is generated in the embryo by signalling gradients of an as yet unknown nature. We searched for transcription factors that transduce this information to the Hox genes. Based on the assumption that the activity levels of such factors might vary with position along the anteroposterior axis, we devised an in vivo assay to detect responsiveness of cis-acting sequences to such differentially active factors. We used this assay to analyze a Hoxb8 regulatory element, and detected the most pronounced response in a short stretch of DNA containing a cluster of potential CDX binding sites. We show that differentially expressed DNA binding proteins are present in gastrulating embryos that bind to these sites in vitro, that cdx gene products are among these, and that binding site mutations that abolish binding of these proteins completely destroy the ability of the regulatory element to drive regionally restricted expression in the embryo. Finally, we show that ectopic expression of cdx gene products anteriorizes expression of reporter transgenes driven by this regulatory element, as well as that of the endogenous Hoxb8 gene, in a manner that is consistent with them being essential transducers of positional information. These data suggest that, in contrast to Drosophila Caudal, vertebrate cdx gene products transduce positional information directly to the Hox genes, acting through CDX binding sites in their enhancers. This may represent the ancestral mode of action of caudal homologues, which are involved in anteroposterior patterning in organisms with widely divergent body plans and modes of development.

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PubMed1997

Hoxb-8 gain-of-function transgenic mice exhibit alterations in the peripheral nervous system.

To understand the developmental role of Hoxb-8, this relatively 5' Hoxb gene was ectopically expressed in embryonic regions where only more 3' Hox genes are normally expressed. Hoxb-8 coding sequences driven by a retinoic acid receptor beta2 promoter fragment were introduced in the mouse germ line by pronuclear injection. The promoter was chosen with the aim to extend rostrally the expression domain of the gene in neurectoderm and mesoderm at the time of development when Hox gene expression domains are being established. Embryos developing from DNA-injected zygotes, and from transgenic mouse lines were analyzed. Pattern alterations were observed in transgenic embryos, some of which involved the peripheral nervous system. Spinal ganglia in the mouse are first detectable around embryonic day 9.5. By day 11.5, the first of these ganglia (C1, Froriep's ganglion) has degenerated in the mouse and other amniotes. In contrast, this first ganglion did persist in the Hoxb-8 gain-of-function transgenic mice. We have started to take advantage of the phenotype of transgenic versus wild-type embryos to understand the mechanisms underlying the ontogeny and degeneration of Froriep's ganglion in wild-type mice, and the role of Hoxb-8 in C1 maintenance in transgenic embryos. The present work describes a morphological, histological and immunocytological analysis of both the degenerating and the permanent C1, and a preliminary characterization of the axonal extensions from the transgenic C1. We discuss the methodology of generating gain-of-function transgenic mice to study the genetics of pattern formation along the antero-posterior axis, and the usefulness of analyzing these particular Hoxb-8 transgenic embryos to understand some aspects of the ontogenesis and development of the upper cervical dorsal root ganglia.

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PubMed1997

A 3' remote control region is a candidate to modulate Hoxb-8 expression boundaries.

Hox genes have been shown to play a key role in the acquisition of positional identity by precursors of embryonic axial, paraxial and limb structures. This function is thought to depend on the sequential, concerted expression of these genes in time and space. However the underlying molecular mechanisms of this collinear expression are still largely unknown. So far we had identified proximal regulatory elements driving expression of Hoxb-8/LacZ transgenes in Hox-like expression patterns with rostral boundaries more posterior than those of the endogenous gene. In this work we have analyzed 30 kb of 3' genomic sequences for Hoxb-8 regulatory activity in transgenic mice. We have identified a control region in the Hoxb-5/b-4 intergenic region that rostrally extends the Hoxb-8/LacZ expression domain into the posterior hindbrain. In combination with the Hoxb-8 minimal promoter, the 3' control region drives transgene expression with boundaries more anterior than those of Hoxb-8 in the neural tube. When combined with a 4.5 kb Hoxb-8 upstream sequence, where essential proximal regulatory sequences are located, the 3' control region drives transgene expression in a domain which seems to correspond to that of the endogenous Hoxb-8. By deletion analysis we have narrowed down to 550bp the regulatory activity interacting with the Hoxb-8 minimal promoter. We discuss the possibility that this remote 3' enhancer, which is the closest regulatory region found in the cluster to rostrally extend Hoxb-8/LacZ expression, could be involved in the regulation of Hoxb-8 and interact with the proximal control elements.

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PubMed1996

The Polycomb-group homolog Bmi-1 is a regulator of murine Hox gene expression.

Drosophila homeotic genes and vertebrate Hox genes are involved in the anteroposterior organization of the developing embryo. In Drosophila, the Polycomb- and trithorax-group genes are required to maintain the homeotic genes throughout development in the repressed or activated state, respectively. The murine Bmi-1 proto-oncogene was shown to exhibit homology to the Polycomb-group gene Posteior sex combs. Mice lacking the Bmi-1 gene revealed posterior transformations along the axial skeleton, whereas transgenic mice overexpressing Bmi-1 display anterior transformations. We have analysed the expression patterns of several Hox genes by RNA in situ hybridization on serial sections of 11.5- and 12.5-day Bmi-1 null mutant embryos. Furthermore, we have analysed the expression of a Hoxc-8/LacZ fusion gene in younger embryos. Our analyses show that Bmi-1 is involved in the repression of a subset of Hox genes from different clusters from at least day 9.5 onwards. We discuss the possibility that members of the murine Polycomb-group can form multimeric protein complexes of different compositions with varying affinity or specificity for different subsets of Hox genes.

Age Factors↗

PubMed1995

Specification of multiple vertebral identities by ectopically expressed Hoxb-8.

We have recently generated Hoxb-8 gain-of-function mutant embryos, using a Hoxb-8 transgene driven by a retinoic acid receptor beta 2 promoter to extend the expression domain to more anterior regions of the embryo (Charité et al. [1994] Cell 78:589-601). Here we describe the phenotype in the axial skeleton of transgenic embryos. The severity of the phenotype was variable, and cervical vertebrae and the base of the skull were affected in different ways. We observed fusion of the anterior arch of the atlas to the dens of the axis, partial splitting of the vertebral body and the neural arch of the axis, and abnormal morphology of the basioccipital and exoccipital bones. The basioccipital bone projected into the atlas, sometimes fusing to the dens of the axis; the exoccipitial bones appeared to be transformed towards neural arch-like structures. A novel pattern of posterior homeotic transformations was observed, involving cervical vertebrae C3 to C7: the ventral aspect of vertebrae C5 to C7 could acquire different morphologies characteristic of more posterior vertebrae: C5 could be transformed into C6, C7, or T1, C6 into C7 or T1, and C7 into T1. Phenotypes of different severity could be arranged into a phenotypic series, starting with the transformation of C7 to T1 and involving transformation of increasingly more anterior vertebrae into increasingly more posterior identities; no vertebra acquired a more posterior morphology than that of the vertebra immediately caudal to it. Ribs appeared to be formed relatively independently of rib heads; cervical ribs (but not rib heads) could be observed as anterior as C3. The results suggest that higher levels of ectopically expressed Hoxb-8 result in specification of more posterior vertebral identities.

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PubMed1995

Regulation of the Hoxb-8 gene: synergism between multimerized cis-acting elements increases responsiveness to positional information.

Hox genes play a key role in the specification of regional development in the vertebrate embryo. They are expressed in regionally restricted domains along the anterior-posterior axis, generally extending from a sharp rostral boundary toward the posterior end. We have studied the regulation of the murine Hoxb-8 gene in vivo using reporter constructs and found that 11 kb of genomic sequences upstream of Hoxb-8 confer a Hox-like pattern of expression on a lacZ reporter gene fused in-frame to the first exon of Hoxb-8. Reporter gene expression was detectable from early stages onwards, but reached rostral expression boundaries in mesoderm and neurectoderm that were more posterior than those of the endogenous gene. Within the upstream region, we have identified several cis-acting elements which are individually capable of driving regionally restricted expression in combination with the Hoxb-8 promoter, and we have investigated their relative contributions to the expression pattern. The results suggest that, in this experimental context, these upstream elements, as well as previously identified elements located within the Hoxb-8 gene, cooperate in setting the rostral expression boundaries. Furthermore, we show that multiple identical copies of cis-acting elements can cooperate, causing a pronounced anterior shift in the expression boundaries. This indicates that the rostral extent of expression is limited by the activity of a transcription factor binding to these elements and that this activity was, at some point in development, higher in precursors of more posterior structures than in precursors of anterior structures. This factor is thus very likely to be involved in the transduction of positional signals.

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PubMed1994

Ectopic expression of Hoxb-8 causes duplication of the ZPA in the forelimb and homeotic transformation of axial structures.

Transgenic embryos were generated carrying a Hoxb-8 transgene under control of the mouse RAR beta 2 promoter, which extends the normal expression domain to more anterior regions of the embryo. These embryos showed mirror-image duplications in the forelimb, analogous to the duplications observed in chick in response to transplantation of a ZPA to the anterior margin of the limb bud. Examination of Sonic hedgehog, Fgf-4, and Hoxd-11 gene expression confirmed that a second ZPA had been generated at the anterior side of the limb bud. Besides other alterations, posterior homeotic transformations of axial structures were observed, involving the first spinal (Froriep's) ganglion and several cervical vertebrae.

Animals↗

PubMed1994

Posterior transformation, neurological abnormalities, and severe hematopoietic defects in mice with a targeted deletion of the bmi-1 proto-oncogene.

The bmi-1 proto-oncogene has been implicated in B-cell lymphomagenesis in E mu-myc transgenic mice. Distinct domains of the Bmi-1 protein are highly conserved within the Drosophila protein Posterior Sex Combs, a member of the Polycomb group involved in maintaining stable repression of homeotic genes during development. We have inactivated the bmi-1 gene in the germ line of mice by homologous recombination in ES cells. Null mutant mice display three phenotypic alterations: (1) a progressive decrease in the number of hematopoietic cells and an impaired proliferative response of these cells to mitogens; (2) neurological abnormalities manifested by an ataxic gait and sporadic seizures; and (3) posterior transformation, in most cases along the complete anteroposterior axis of the skeleton. The observations indicate that Mbi-1 plays an important role in morphogenesis during embryonic development and in hematopoiesis throughout pre- and postnatal life. Furthermore, these data provide the first evidence of functional conservation of a mammalian Polycomb group homolog.

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PubMed1993

Two phases in the establishment of HOX expression domains.

Vertebrate HOX genes are thought to play a role in the transmission of anteroposterior (A-P) positional information to the cellular precursors of embryonic axial and paraxial structures. We present an in situ analysis of the expression of two adjacent HOX genes, Hox-2.3 and Hox-2.4. We discuss the data on early gene expression in the light of what is known about cell behavior, cellular fate maps, and A-P regionalization during gastrulation. After the genes are switched on in the most posterior part of the embryo at the late primitive streak stage, the expression domains spread, in a way that does not correlate with cell lineage, toward more cranial positions within and along the streak in mesoderm and ectoderm. A second phase of HOX gene expression takes place at the early somite stage after the expression domains have reached the region around and lateral to the anterior part of the streak (the equivalent of the chicken Hensen's node). HOX gene expression during this second phase is probably clonally transmitted and would be directly associated with the acquisition of A-P positional identity by the progenitors of paraxial mesoderm and neurectoderm which are located anterolaterally to the node.

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PubMed1993

Proximal cis-acting elements cooperate to set Hoxb-7 (Hox-2.3) expression boundaries in transgenic mice.

The Hox genes have been proved to be instrumental in establishing the positional identity of cells along the embryonic anteroposterior (A-P) axis. Studying the regulation of these genes is a first step toward elucidating the molecular basis of regionalization during embryogenesis. We report here on the identification of cis-acting elements controlling the expression of Hoxb-7 (Hox-2.3). We show that elements driving A-P restricted gene expression are located within the 3.5 kb proximal upstream sequences of the Hoxb-7 gene. A deletion analysis provides evidence for at least three cis-acting control elements upstream from Hoxb-7, and for cooperative interactions between some of these elements in generating the A-P restricted transgenic pattern. One element, conferring by itself Hox-like expression boundaries to the transgene, has been studied in more detail and found to act in an orientation-and promoter-dependent manner. Together the 3.5 kb sequences proximal to Hoxb-7 mediate A-P restricted Hoxb-7/lacZ gene expression in a domain showing rostral boundaries more posterior than those of Hoxb-7. The evolution throughout embryogenesis of the expression pattern of a transgene carrying these sequences has been analysed and shown to mimick that of the endogenous gene, except for a slight delay in the initial expression. We conclude that the transgenes that we tested, spanning a total of 27 kb genomic sequences, do not reproduce all the features of the Hoxb-7 expression pattern. The differences in expression between Hoxb-7 and the transgenes may reveal an aspect of the Hox regulation for which either remote cis-acting control elements and/or gene clustering is required. Additional features that may have favoured maintenance of clustered organisation during evolution are partial overlap of transcription units with the regulatory regions of the neighbouring genes, and cis-regulatory interactions between multiple Hox genes: not only do cis-acting control elements of the Hoxb-7 gene map in the 3' untranslated sequences of the Hoxb-8 (Hox-2.4) gene, but our experiments suggest that Hoxb-7 control sequences modulate expression of the Hoxb-8 gene as well.

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PubMed1992

The murine Hox-2.4 promoter contains a functional octamer motif.

Like other HOX genes the murine Hox-2.4 gene is thought to be involved in regional specification along the antero-posterior axis. In addition it has been reported to have oncogenic potential. We studied expression Hox-2.4 in murine EC cells and determined the transcription start site. Studies of DNA-protein interactions in the promoter region showed that the Hox-2.4 promoter contains a CCAAT box and a perfect octamer motif, which is capable of binding Oct-factors. Cotransfection of Oct expression vectors influences the transcriptional activity of the promoter, suggesting that the Oct-gene family may be involved in regulating HOX genes.

Animals↗

PubMed1992

Mammalian homeobox genes in normal development and neoplasia.

This review aims at providing an evaluation of the currently available data concerning the role of homeobox genes in mammalian embryonic pattern formation, and their involvement in oncogenic processes. The literature dealing with mouse and human homeobox genes is covered, with some excursions into Xenopus and chicken work because studies regarding particular aspects of development in the latter systems often complement those in mammals. Other studies in amphibians, chicken, and fish are omitted as they fall outside the scope of this survey devoted to mammalian genes. Emphasis is placed on expression and regulation during normal embryogenesis, on present hypotheses regarding gene function, on effects on development of modifying the expression patterns, and on observed aberrations in structure or expression associated with and possibly causally linked to neoplasia. The studies specifically dealing with the structure of the homeodomain and the mechanism of its interactions with DNA, which have been recently reviewed, are not considered here. The most thoroughly studied mammalian homeobox genes bear sequence homology to the Drosophila Antennapedia (Antp) homeotic gene and are thought to be involved in determination of regional identity along the anteroposterior (A-P) axis. Studies on these genes, the HOX genes, are oftem compared with related investigations in flies. In addition to the HOX genes, a number of genes containing a homeobox related to that in other Drosophila developmental control genes have been isolated from the mammalian genome and are being intensively studied. Homeodomains divergent from the Antp prototype have been discovered in an increasing number of transcription factors. Some of these may play a crucial role in local pattern formation, while others are tissue-specific or ubiquitous transcription regulators. As is unsurprising of genes, whose products regulate transcription, some of the homeobox-containing genes have been associated with malignancy, usually on the basis of abnormal structure, or deletions found to occur in tumor cells. The degree of probability that these mutated forms were causative in the generation of the tumors in which they were found is discussed.

Amino Acid Sequence↗

PubMed1991

Characterization of the murine Hox-2.3 promoter: involvement of the transcription factor USF (MLTF).

The murine homeobox-containing gene Hox-2.3 contains a basal promoter in a 210-bp region upstream of the transcription start site. In vitro studies of DNA-protein interactions in this region, and in a 1.3-kb upstream region which is known to play a role in tissue specific expression in vivo, led to the identification of DNA elements interacting with nuclear proteins from embryocarcinoma cells. Among the factors binding to the basal promoter is the upstream stimulating factor (USF), also known as major late transcription factor (MLTF). A single point mutation in its binding site abolishes binding in vitro and leads to 50% reduction of the transcriptional activity as measured in receptor gene experiments, showing that it is an activator of Hox-2.3 expression.

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PubMed1991

The mouse homeobox gene, S8, is expressed during embryogenesis predominantly in mesenchyme.

The murine S8 gene, originally identified by Kongsuwan et al. [EMBO J. 7(1988)2131-2138] encodes a homeodomain which resembles those of the paired family. We studied the expression pattern during mid-gestation embryogenesis of S8 by in situ hybridization. Expression was detected locally in craniofacial mesenchyme, in the limb, the heart and the somites and sclerotomes all along the axis, and was absent from the central and peripheral nervous system, splanchnopleure, and endodermal derivatives. This pattern differs considerably from that of most previously described homeobox containing genes. By genetic analysis, the gene was located on chromosome 2, about 20 cM from the HOX-4 cluster.

Amino Acid Sequence↗

PubMed1990

Hox-2.3 upstream sequences mediate lacZ expression in intermediate mesoderm derivatives of transgenic mice.

The mouse Hox-2.3 gene contains an Antp-like homeobox sequence and is expressed in a spatially restricted anteroposterior domain during development. To study the molecular basis of this differential gene regulation, we set out to characterize the cis-regulatory elements mediating Hox-2.3 expression during embryogenesis. We show that a fragment extending 1316 base pairs (bp) upstream of the transcription start site, thus corresponding to the Hox-2.4/Hox-2.3 intergenic sequences is capable of mediating luciferase gene transcription in transfected cells in vitro and lacZ expression in transgenic mice. The beta-galactosidase-staining pattern in embryos was found to be strikingly similar to the Hox-2.3 in situ hybridization pattern in intermediate mesoderm derivatives: high levels of both Hox-2.3 transcripts and beta-galactosidase activity were found in the mesonephric duct-derived epithelium of the meso- and metanephric kidney and associated ducts, from the time these structures first appeared on throughout development. The transgene apparently lacks sequences needed for correct Hox-2.3 expression in somitic and lateral plate mesoderm and in neurectoderm. These results document the involvement of distinct regulatory elements in Hox gene expression in subsets of cells with distinct developmental fate, situated at similar positions along the anteroposterior axis of the embryo.

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