Elements of transcription factor network design for T-lineage specification.

The complex spectrum of cell types produced in mammalian hematopoiesis can be understood as the output of highly combinatorial transcription factor action. The generation of multiple diverse combinations of transcription factors from the common starting state of the hematopoietic stem cell must be explained through the cross-regulatory interactions of these transcription factors at several levels. Here, the operation of such a network is addressed through a focus on murine T cell development, where we have recently established regulatory linkages between GATA-3 and PU.1 and multiple other factors essential to this differentiation pathway. The action of both essential/rate-limiting factors and factors with effects that shift qualitatively with dose and time of action can be traced through the regulatory interaction network. Hypothetical models are proposed to indicate the network nodes that are differentially activated in normal T cell lineage progression and in cells diverted to other potential fates.