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Biomedical subjects

Stephen J Gaunt

Publications and source records attributed to Stephen J Gaunt.

5 recordsLinked to original sources
PubMed2005

cdx4/lacZ and cdx2/lacZ protein gradients formed by decay during gastrulation in the mouse.

Expression of the mouse caudal genes cdx4 and cdx2 is examined by use of lacZ reporter constructs expressed in transgenic mouse embryos. During early gastrulation, up to at least 8.5 days of development, reporter mRNA distributions are apparently similar to those of endogenous cdx mRNAs. By 8.25 to 8.8 days, cdx/lacZ protein activities have become distributed as posterior-to-anterior gradients along the neural and mesoderm tissues. The gradients form by decay of activity as cells become distanced from the regressing tailbud. In situ hybridization studies indicate that the decay is primarily in cdx/lacZ protein activities rather than mRNAs. As gastrulation proceeds, the locations of the gradients regress progressively posteriorly along the growing axis. Our results indicate how cdx4 and cdx2 protein gradients might be generated by decay during normal development. The smoothness of the gradients that we detect shows that there cannot be extensive mixing of cells once they leave the tailbud to contribute to the growing axis. An enhancer element located in the first intron of the cdx4 gene is essential for correct transgene expression.

Animals↗
PubMed2004

Additional enhancer copies, with intact cdx binding sites, anteriorize Hoxa-7/lacZ expression in mouse embryos: evidence in keeping with an instructional cdx gradient.

Expression of a Hoxa-7/lacZ reporter construct in transgenic mouse embryos is shifted anteriorly when the upstream enhancer is multimerized. The shift occurs in spinal ganglia, neurectoderm and in both paraxial and lateral plate mesoderms. Much of the multimer effect is inhibited by destruction of a single caudal (cdx) binding motif in the additional copies of the enhancer. These observations are in agreement with earlier enhancer multimerization analyses made for Hoxb-8 (Charite et al., 1998). Our findings therefore provide further evidence that the anterior limit of a Hox gene's expression domain is normally dependent upon and is determined by, the dosage of transcription factor(s) which bind to its enhancer element(s) and that these factors may be, or must include, the cdx proteins. We consider these findings in terms of both instructional (morphogen-like) gradient and timing models for the establishment of Hox gene expression domains. Enhancer multimerization results in an earlier onset of Hoxa-7/lacZ activity in the embryo. In neurectoderm at 8.7 days and in mesoderm at 10.5 days, the anterior boundaries of expression are located posterior to those seen at some earlier stages of development. We discuss how these findings are in keeping with a model where Hox expression boundaries become set along instructional cdx gradients, formed by cdx decay in cells moving away from the primitive streak region.

Amino Acid Motifs↗
PubMed2003

Vertebrate caudal gene expression gradients investigated by use of chick cdx-A/lacZ and mouse cdx-1/lacZ reporters in transgenic mouse embryos: evidence for an intron enhancer.

The vertebrate caudal proteins, being upstream regulators of the Hox genes, play a role in establishment of the body plan. We describe analysis of two orthologous caudal genes (chick cdx-A and mouse cdx-1) by use of lacZ reporters expressed in transgenic mouse embryos. The expression patterns show many similarities to the expression of endogenous mouse cdx-1. At 8.7 days, cdx/lacZ activity within neurectoderm and mesoderm forms posterior-to-anterior gradients, and we discuss the possibility that similar gradients of cdx gene expression may function as morphogen gradients for the establishment of Hox gene expression boundaries. Our observations suggest that gradients form by decay of cdx/lacZ activity in cells that have moved anterior to the vicinity of the node. The cdx-A/lacZ expression pattern requires an intron enhancer that includes two functional control elements: a DR2-type retinoic acid response element and a Tcf/beta-catenin binding motif. These motifs are structurally conserved in mouse cdx-1.

Amino Acid Motifs↗
PubMed2002

Colinearity and non-colinearity in the expression of Hox genes in developing chick skin.

Hox genes are usually expressed temporally and spatially in a colinear manner with respect to their positions in the Hox complex. We found that these characteristics apply to several Hox genes expressed in developing chick skin (Hoxb-4, Hoxa-7 and Hoxc-8), and we classed this group of genes as regionally restricted. To our surprise, we found that most of the Hox genes we examined are regionally unrestricted in their expression in the embryonic chick skin. This second group includes the Hoxd genes, Hoxd-4 to Hoxd-13, Hoxa-11 and Hoxc-6. Temporally, the expression of the regionally restricted genes can be observed by E5 within the epidermis, whereas the spatially unrestricted genes are not expressed in the epidermis until E6.25. Unexpectedly, we found that all the unrestricted genes are expressed concomitantly and therefore do not conform to temporal colinearity. Moreover, the dermal expression for both groups occurs later, but maintains the same anteroposterior patterning to that seen previously in the epidermis. During embryonic day 7-8, expression for all genes is up-regulated within the dense dermis whilst being reduced within the inter-bud regions. Later expression within the bud mesenchyme is down-regulated whilst high levels of transcriptional activity are detectable within the epidermal sheath of each feather bud. These results indicate that the transcriptional activity of Hox genes in the developing chick skin could be important during embryonic skin patterning both by providing regionally restricted positional cues, and also by imparting generic signals necessary for feather morphology.

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