LDB1 Is Required for the Early Development of the Dorsal Telencephalon and the Thalamus.

LIM domain binding protein 1 (LDB1) is a protein cofactor that participates in several multiprotein complexes with transcription factors that regulate mouse forebrain development. Since null mutants display early embryonic lethality, we used a conditional knockout strategy to examine the role of LDB1 in early forebrain development using multiple Cre lines. Loss of from E8.75 using Foxg1Cre caused a disruption of midline boundary structures in the dorsal telencephalon. While this Cre line gave the expected pattern of recombination of the floxed locus, unexpectedly, standard Cre lines that act from embryonic day (E)10.5 (Emx1Cre) and E11.5 (NesCre) did not show efficient or complete recombination in the dorsal telencephalon by E12.5. Intriguingly, this effect was specific to the floxed allele, since three other lines including floxed Ai9 and mTmG reporters, and a floxed line, each displayed the expected spatial patterns of recombination. Furthermore, the incomplete recombination of the floxed locus using NesCre was limited to the dorsal telencephalon, while the ventral telencephalon and the diencephalon displayed the expected loss of . This permitted us to examine the requirement for LDB1 in the development of the thalamus in a context wherein the cortex continued to express . We report that the somatosensory VB nucleus is profoundly shrunken upon loss of LDB1. Our findings highlight the unusual nature of the locus in terms of recombination efficiency, and also report a novel role for LDB1 during the development of the thalamus.