Patterning and compartment formation in the diencephalon

Abstract

The diencephalon gives rise to structures that play an important role in connecting the anterior forebrain with the rest of the central nervous system. The thalamus is the major diencephalic derivative that functions as a relay station between the cortex and other lower order sensory systems. Almost two decades ago, neuromeric/prosomeric models were proposed describing the subdivision and potential segmentation of the diencephalon. Unlike the laminar structure of the cortex, the diencephalon is progressively divided into distinct functional compartments consisting principally of thalamus, epithalamus, pretectum, and hypothalamus. Neurons generated within these domains further aggregate to form clusters called nuclei, which form specific structural and functional units. We review the recent advances in understanding the genetic mechanisms that are involved in the patterning and compartment formation of the diencephalon.

Keywords: Gbx2; Shh; ZLI; compartment boundary; fate mapping; organizer; prosomere; thalamus.

Figure 1

Schematic representation of a sagittal view of the various domains of the diencephalon in mouse embryos at E12.5. The prosomere model predicts that the diencephalon consists of three principal prosomeres/segments. Prosomere1 (p1) corresponds to the pretectum and p3 corresponds to the prethalamus. The p2 domain consists of the progenitor domains of the rostral thalamus (rTh), the caudal thalamus (cTh), and the epithalamus. The progeny of the latter give rise to the Gbx2-positive thalamus proper. The ZLI wedge arises from the Shh positive basal plate and acts as an organizer. The entire area shaded in gray indicates the neural tube. Ncx: Neocortex.