HOXGENE EXPRESSION IN ADULT TISSUES WITH PARTICULAR REFERENCE TO THE ADRENAL GLAND

Abstract

In comparison to the embryo, very little work has been carried out on the expression and role of Hox genes in the adult animal. An expression profile of all 39 vertebrate Hox genes on a select panel of adult human tissues reveals that in fact these genes are widely expressed throughout the adult human and a colinear pattern of expression is displayed similar to that of the developing embryo. Of particular interest is the abundance of Hox genes that are expressed within the adult adrenal gland. Adrenal cortical cells are continuously renewed to sustain production of zonal steroids. Cell proliferation occurs at the periphery of the cortex and cells are then displaced centripetally, phenotypically switching as they migrate through the gland before undergoing apoptosis at the zona reticularis/medullary boundary. It is still unclear which mechanisms cause the cells to differentiate as they cross the zonal boundaries and we hypothesise that Hox genes may be involved in the phenotypic switching of the adrenocortical cells. In situ hybridisation experiments were carried out on adult rat adrenal gland sections and Hox gene expression was localized within the zonal borders, coinciding with the localization of cells that undergo phenotypic differentiation, and thus supporting our hypothesis that Hox genes may be involved in the phenotypic switching of the adrenocortical cells. As in the developing embryo, the genes display colinear expression with the 3' Hox genes being expressed within the outer gland and the 5' genes within the inner zones.

Evolution of coding and non-coding genes in HOX clusters of a marsupial

“…In adults, HOX genes continue to be expressed and thereby retain developmental plasticity in certain tissues or maintain homeostasis. However, there has been much less work on gene expression in adult tissues compared to developing tissues [45,46]. We showed that HOX gene expression in adult marsupial tissues was tissue-specific and differentially expressed (Figure  3).…”

Integration of transcriptome and methylome analysis of aldosterone-producing adenomas

“…It is noteworthy that some of the HOX family genes (HOXA7, HOXA11, and HOXB9) are up-regulated in APA relative to AAG. A previous report demonstrated that 23 out of 39 HOX cluster genes are expressed in human adrenal glands and that HoxB2, B4, B5, and B9 are expressed in order from the capsule to the inner zona reticularis in the rat adrenal cortex (29). Because some HOX genes are involved in cellular differentiation and tumorigenesis (45), it is interesting to speculate that aberrant HOX gene activation contributes to tumorigenesis in APA.…”

“…We identified several genes that were up-regulated in APA that were not reported previously (Supplementary Table 4). These included the HOX gene family, which has been shown to play a crucial role in adrenal zonation (29). A heat map representation of the HOX gene family revealed increased expression of HOXA7, HOXA11, and HOXB9 in APA relative to AAG (Fig.…”

Antisense oligonucleotide mediated knockdown of HOXC13 affects cell growth and induces apoptosis in tumor cells and over expression of HOXC13 induces 3D-colony formation

“…Colinear expression of different HOX genes are crucial for proper cell differentiation and development (11, 12). In addition to their crucial roles in embryonic development, HOX gene appeared to play important roles in postnatal development (13). Various HOX genes such as HOXA5, HOXA7, HOXA10 etc are shown to be important for cell cycle regulation (14).…”