The rat gene homologous to the human gene 9-27 is involved in the development of the mammary gland

We have developed a model system for studying differentiation in the mammary gland, by using two clonal cultures deriving from a rat breast adenocarcinoma, They differ in the ability to form domes, structures the significance of which is unknown. By using the subtractive cDNA library approach, we isolated a cDNA that is highly expressed in the dome-forming cells, and identical to the rats gene and highly homologous to the human 9-27 gene, Antisense treatment of the dome-forming cells specifically and reproducibly abolishes dome formation, while forced expression of the gene in non-dome-forming cells causes morphological changes suggestive of "flat" domes, In situ hybridization on rat tissues shows that the gene is expressed in epithelia, especially in those forming tubular structures, suggesting a relatedness between these structures and domes, Cytokeratin 8 and E cadherin are strongly expressed in the domes but not outside them, suggesting that the rats gene triggers the cells to express molecules that tighten the lateral connections between the cells; the process is likely to parallel that occurring during the differentiation of the mammary gland.