Signaling mechanisms in pituitary morphogenesis and cell fate determination

The development of the pituitary gland has provided an instructive model sy stem for exploring the mechanisms by which differentiated cell types arise from a common primordium in response to extrinsic and intrinsic signals. Re cent studies have established that organ commitment, early patterning, prol iferation and positional determination of cell types in the developing pitu itary are mediated through the integral actions of multiple signaling gradi ents acting on an initially uniform ectodermal cell population. Studies of the cell-autonomous transcriptional mediators of the transient signaling ev ents have also provided insight into the molecular mechanisms by which over lapping patterns of transcription factor expression can positionally specif y pituitary cell lineages. There is emerging evidence for a morphogenetic c ode for the development of the pituitary gland based on the cooperative and opposing actions of multiple signaling gradients, mediated by correspondin g expression patterns of temporally and spatially induced transcription fac tors.