Investigation into the role of HOX factors in gonad and adrenal steroidogenesis

The gonad and adrenal cortex are derived from a common progenitor cell population and actively produce steroids during embryonic development. The regulation of steroid production in these organs and the factors that account for steroid specificity are not well understood. In this proposal we aim to investigate the role of members of the HOX family of transcription factors in the regulation of steroid production in the gonad and adrenal. HOX factors have been shown to regulate patterning in the embryo and our preliminary experiments indicate that they contribute to organ specific steroid production. We have identified HOXB9 as being expressed in the adrenal cortex but not the gonad and, conversely, we have identified HOXD9 as being gonad, but not adrenal, specific. Misexpression of HOXB9 in the gonad of transgenic mice gave rise to an increase in the presence of genes encoding enzymes involved in adrenal specific steroid production. We plan to use a combination of approaches including analysis of transgenic mice and tissue and organ culture experiments to determine the role of these HOX factors in steroidogenesis. As an extension of these studies we will investigate the ability of HOXB9 to cooperate with the nuclear hormone receptor SF-1 to induce the differentiation of adrenal steroid production in embryonic stem (ES) cells. SF-1 is a nuclear hormone receptor that has been shown to be required for the differentiation of steroid producing cells of the gonad and adrenal and can induce some aspects of steroid production in ES cells. Our studies will further these observations and may provide a framework for the production of steroid producing cells that may contribute to the development of novel therapies for patients with adrenal and gonadal failure.

The transcriptional regulation of steroid production by the gonad and adrenal is not well characterised and the factors contributing to steroid specificity are not known. In this proposal we will use transgenic mice and tissue and organ culture approaches to investigate the role of members of the HOX family of transcription factors in the regulation of steroid production and specificity in the gonad and adrenal. Our preliminary studies show that HOXB9 is found in cells of the developing adrenal cortex but not the gonad. Misexpression of this factor in the gonad of transgenic mouse embryos revealed an upregulation of expression of Cyp21 and Cyp11b1, which encode adrenal specific steroidogenic enzymes. We have also identified HOXD9 as expressed in the embryonic testis, which produces testosterone, but not in the adrenal. We aim to misexpress this factor in adrenal cortical cells and investigate the expression of gonad specific steroidogenic enzymes. We will engineer repressor versions of these HOX factors and analyse their effect when expressed in adrenal and gonadal tissue. The nuclear hormone receptor SF-1 has been shown to be important in the development of the gonad and adrenal cortex as these organs fail to form in Sf-1 mutant mice. Previous studies have indicated that SF-1 is a general regulator of steroidogenic genes and expression of this factor in embryonic stem (ES) cells induces these cells to be active in the initial step of steroid production from cholesterol. In this proposal we also aim to investigate if HOXB9 can cooperate with SF-1 to induce adrenal specific steroidogenesis in ES cells. These studies will provide novel insight into the mechanisms of transcriptional regulation of specificity in the differentiation of steroid producing cell types of the adrenal and gonad. The proposed work will also determine the contribution of HOX factors to the regeneration of steroid producing cells that may aid in the development of novel therapies for patients with adrenal and gonadal failure.