Figure 1.

Interdependence of prolactin receptor (PrlR) and signal transducer and activator of transcription 5 (Stat5) signaling. (a) The 'classical' PrlR-Jak2-Stat5 pathway contributes to alveolar development. (b) Alternative routes to activate Stat5 are required for alveologenesis. (c) Potential contribution of multiple PrlR-dependent pathways to the proliferative response to estrogen and progesterone. PI-3K, PI 3-kinase; MAPK, mitogen-activated protein kinase.