Since my days as a graduate student with Klaus Kratochwil in Salzburg, Austria, I have been studying many aspects of mammary gland development. Using targeted gene strains, I analyzed a number of mutants with defects in mammary gland development to identify genes that regulate ductal and alveolar development during puberty and pregnancy. Among them are activinB, the transcription factors C/EBPbeta, and ID-2, Shh, connexins, SOCS3, and Notch signals. Presently, I am investigating the role of the Jak2/Stat5 pathway in the proliferation and differentiation of secretory epithelial cells. I also study the epigenetic alterations that regulate these events. I collaborate with several researchers who perform mammary epithelial transplantations, particularly of anlagen from mutants that do not survive to adulthood.