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ABSTRACT

The orphan nuclear receptor steroidogenic factor 1 (SF-1) plays key roles in endocrine development and function. Initially identified as a positive regulator of the cytochrome P450 steroid hydroxylases, analyses of knockout mice deficient in SF-1 revealed that SF-1 is essential for adrenal and gonadal development, pituitary gonadotropin expression and formation of the ventromedial hypothalamic nucleus. Although more limited in scope, analyses of SF-1 in humans similarly have suggested that SF-1 is important for differentiated function in adrenocortical and gonadotrope adenomas. In the hope of extending our understanding of SF-1 function by identifying possible roles of SF-1 in clinical endocrine disorders, we isolated the FTZ-F1 gene encoding human SF-1 and mapped it to chromosome 9q33. In this report, we characterize the sequence and structural organization of the human cDNA and gene encoding SF-1, providing new insights into comparative aspects of SF-1 structure that will facilitate efforts to study the role of this transcription factor in human endocrine disorders.

ABSTRACT

After weaning, the mammary gland ceases lactation and involutes. The wet weight of the gland decreases by 70% within 4 days of weaning. This involves significant tissue remodelling as the ducts regress and return to the resting state. The presence of apoptotic bodies in the luminal epithelial compartment 2 to 3 days after weaning provides clear evidence that a substantial proportion of the regression is attributable to the induction of active cell death (ACD) of the epithelial cells.

These changes in the architecture of the gland were found to be mirrored by changes in gene expression. The steady-state level of β-casein mRNA decreased rapidly after weaning from the high levels seen during lactation to undetectable levels by 8 days after weaning. The steady-state levels of expression of a number of genes associated with ACD, including TRPM-2, tissue transglutaminase (TGase) and poly(ADP-ribose) polymerase (PARP), increased transiently during this time-frame. The steady-state level of TRPM-2 mRNA increased 2 days after weaning, reaching a peak on day 4, and decreasing to undetectable levels by day 8 after weaning. The steady-state levels of two other mRNAs, TGase and PARP, showed very similar kinetics. In contrast, the mRNA for Hsp 27, which has been shown to be induced during prostate regression, was not significantly induced in the regressing mammary gland. In-situ hybridization demonstrated that the TRPM-2, TGase and PARP genes were expressed predominantly in the luminal epithelial cells of the ducts. These cells expressed β-casein mRNA during lactation, and underwent ACD after weaning.

While the ultrastructural changes in the mammary gland after weaning, and the induction of TRPM-2, TGase and PARP mRNAs, are reminiscent of apoptosis in the prostate, several features of the process are different. Most notably, the disruption of the secretory processes and the lack of increased expression of Hsp 27 in the regressing mammary gland suggest that there may be a number of important events in ACD that are not common to all cells.