Determining the fate of Shh-expressing cells in the diencephalon using a BAC transgenic reporter

The thalamus and prethalamus consist of multiple distinct nuclei and their boundary is demarcated by the zona limitans intrathalamica (ZLI). The development of the primordial thalamus and prethalamus proceed within the caudal diencephalon. Shh has been shown to be essential for diencephalic patterning and regionalization. To understand the role of Shh in the specification of distinct thalamic and prethalamic nuclei, we developed a lineage marker for diencephalic cells expressing Shh by using bacterial artificial chromosome (BAC) transgenesis. A genomic fragment containing ∼210 kb of the mouse Shh locus was used to target enhanced green fluorescent protein (eGFP) in transgenic mice. This transgenic BAC reporter faithfully mimicked the pattern of endogenous Shh expression in the caudal diencephalon, including the ZLI. Fate mapping analysis at multiple developmental stages showed that descendents of Shh-expressing progenitor cells derived from ZLI contribute to a population of cells in the ventral lateral geniculate nucleus.