Building a bridal chamber: development of the thalamus.

The thalamus is a central brain region that plays a crucial role in distributing incoming sensory information to appropriate regions of the cortex. The thalamus develops in the posterior part of the embryonic forebrain, where early cell fate decisions are controlled by a local signaling center - the mid-diencephalic organizer - which forms at the boundary between prospective prethalamus and thalamus. In this review we discuss recent observations of early thalamic development in zebrafish, chick, and mouse embryos, that reveal a conserved set of interactions between homeodomain transcription factors. These interactions position the organizer along the neuraxis. The most prominent of the organizer's signals, Sonic hedgehog, is necessary for conferring regional identity on the prethalamus and thalamus and for patterning their differentiation.