Mammary gland involution is a regressive process for the gland to return to its prepregnancy state after lactation and comprises an initial reversible and second remodeling stage. Although many genes and the multiple expression profiles of their mRNAs have been found in this process, the mechanisms controlling the profiles are largely unknown. In this study, we identified and analyzed transcription factor Sox4 in mammary gland involution. Elevated expression of Sox4 gene in the first stage (48 h after weaning) was observed at the mRNA and protein levels in the mouse mammary gland. Immunohistochemistry of the involuting gland indicated that Sox4 was located in the nuclei of epithelial cells. Nuclear Sox4 was also detected in the second stage, but unlikely to be involved in cell death, one of the characteristic events of involution. To clarify the functional roles of Sox4 in involution, we introduced a model, including a normal mammary epithelial cell line, for finding candidate target genes of this transcription factor and examined its effect on tenascin C mRNA expression.
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