Apoptosis in the rat mammary gland and ventral prostate: Detection of cell death-associated genes using a coincident-expression cloning approach

Apoptosis plays a striking role in the hormone-dependent involution of the mammary gland, but it has proved difficult to distinguish between the 'cell death' associated genes and the 'tissue remodelling' genes which are expressed concurrently. To identify cell death-associated genes, we have established a 'coincidence analysis', based on the previously described 'RNA differential display' method of Liang and Pardee (1992). Coincidence analysis allows the detection of genes expressed during related processes in different organs and was employed here to identify transcripts in which expression patterns are seen to be associated with apoptosis during involution of both rat mammary- and the ventral prostate glands. That the coincidence analysis is a promising approach can be seen from the fact that while widely accepted apoptosis markers such as transglutaminase (Fesus et al, 1987; Strange et al, 1992) and sulfated glycoprotein-2 (Buttyan et al, 1989; Strange et al, 1992; Guenette et al, 1994) exhibited similar expression in both regressing tissues, transcription of tissue remodelling enzymes was minimal in the involuting prostate. We describe here the characteristics of five clones isolated which show coincident expression during programmed cell death in mammary and prostate tissues. Partial sequence analysis revealed for three clones high homologies with previously described genes; the putative rat homolog of the growth arrest gene gas-1 (Schneider et al, 1988; Del Sat et al, 1992), a homolog of the mouse 'Integrin Associated Protein' (IAP) (Brown et al, 1990; Lindberg et al, 1993) and the sequence encoding for the 'Allograft inflammatory Factor' AIF-1 (Autieri et al, 1995; Utans et al, 1995). One clone displayed homology with an expressed human sequence tag and one clone unrelated to any known DNA sequence was isolated. The expression of these genes in involuting rat mammary and ventral prostate, was correlated with that in other organs and in situ hybridization was applied to establish that the secretary epithelial cells which undergo programmed cell death are the site of elevated expression during the course of involution. Furthermore, we conclude that the coincidence analysis approach described here could be easily applied to facilitate the characterization of gene expression i.e. for the detection and comparison of hormonally regulated genes in different organs.