HOX Protein Function in Development and Disease
My laboratory is focused on discerning the molecular functions of vertebrate Hox proteins in normal development and disease. The Hox proteins are an evolutionarily conserved group of helix turn helix transcription factors that exhibit remarkable conservation in sites of expression, chromosomal clustering, and loss of function phenotypes in both vertebrate and invertebrate species.
In humans and mice, there are 39 Hox genes, which have been shown to be required for the proper development of many tissues and structures including the vascular endothelia, hand and foot skeletal elements, the external genitalia, bladder, ureter, and kidney.
How Hox proteins actually control the formation of specific embryonic regions is poorly understood. Indeed, while it is known that Hox proteins bind DNA to facilitate gene expression, the actual DNA sequences bound by these proteins, as well as the interacting factors that help modulate specific transcriptional functions, are largely unknown. As these proteins regulate development or contribute to a disease state by controlling target gene expression, a major emphasis of our research group is to define the DNA sequences used by these transcription factors to regulate the expression of specific target genes. Through the identification of specific HOX transcription factor binding sites and the cis-regulatory elements necessary to regulate target gene expression, the HOX programs necessary for tissue development or causative in a disease state can be identified. Finally the developmental programs regulated by HOX proteins can also be used to repair/regenerate tissues affected by injury or disease.
Limb Development and Postnatal RegenerationWe have generated knockout mice bearing mutations in Hoxa13 and Hoxd13 to examine their functions in the developing limb. While similar in their expression patterns, the Hoxa13 and Hoxd13 mutant phenotypes are remarkably different. Indeed while Hoxa13 mutants exhibit an absence of many autopod (hand or foot) skeletal elements, Hoxd13 mutants exhibit an opposite phenotype with additional digits and an overgrowth of cartilage and bone in the joints and interdigital tissues. Read more.
Biochemistry of HOX Protein DNA Binding
The Stadler Laboratory uses the systematic evolution of ligands by exponential enrichment (SELEX) approach (invented by Larry Gold at the University of Colorado, Boulder) to identify individual HOX protein binding sites. Our adaptation of the SELEX approach, uses purified HOX proteins to identify their preferred binding site from a random mixture of DNA binding sites (see figure below). HOX protein DNA complexes are fractionated on acrylamide gels and the DNA protein complex can be identified by the change in electrophoretic mobility. Read more.
Development of the External Genitalia and Hypospadias
In humans and mice, mutations in Hoxa13 cause hypospadias, a common birth defect affecting the growth and closure of the external genitalia. In humans, hypospadias affects 1 in 125 live male births each year making this malformation one of the most prevalent defects in industrialized nations including the United States. Read more.
Bladder-Ureter Integration and Vesicouretal Reflux
Vesicouretal reflux is a common urologic defect caused by incorrect flow of urine from the bladder to the kidneys causing expansion of the ureter and kidney damage. The Hoxa13 mutant mouse models this defect. A comparative analysis of genes expressed in Hoxa13 heterozygous control (+/-) and homozygous mutant (-/-) mice using Affymetrix microarrays and ChIP-seq have identified several candidate genes we are currently investigating for a role in bladder/ureter integration and direct regulation by HOXA13. Read more.