Lhx6 regulates the migration of cortical interneurons from the ventral telencephalon but does not specify their GABA phenotype

The LIM homeodomain family of transcription factors is involved in many processes in the developing CNS, ranging from cell fate specification to connectivity. A member of this family of transcription factors, lhx6, is expressed in the medial ganglionic eminence(MGE) of the ventral telencephalon, where the vast majority of cortical interneurons are generated. Its expression in the GABA-containing MGE cells that migrate to the cortex suggests that this gene uniquely or in combination with other transcription factors may play a role in the neurochemical identity and migration of these neurons. We performed loss of function studies for lhx6 in mouse embryonic day 13.5 brain slices and dissociated MGE neuronal cultures using Lhx6-targeted small interfering RNA produced by a U6 promoter-driven vector. We found that silencing lhx6 impeded the tangential migration of interneurons into the cortex, although it did not obstruct their dispersion within the ganglionic eminence. Blocking lhx6 expression in dissociated MGE cultured neurons did not interfere with the production of GABA or its synthesizing enzyme. These results indicate that lhx6, unlike the closely related member lhx7, does not regulate neurotransmitter choice in interneurons but plays an important role in their migration from the ventral telencephalon to the neocortex.