Finally, genetic rescue experiments reveal that Cdh11 is one of the targets of the Bhlhb5/Prdm8 repressor complex whose upregulation in the absence of the Bhlhb5/Prdm8 repressor complex contributes to the abnormal phenotype observed in Bhlhb5 and Prdm8 mutant

mice. Taken together, these findings suggest that Bhlhb5 and Prdm8 are obligate components of a transcriptional repressor complex. Bhlhb5 binds to specific DNA within the regulatory regions of its target genes and recruits Prdm8 to mediate repression of the transcription of these targets. In the absence of Bhlhb5 or Prdm8 the gene targets are upregulated resulting in abnormal development of specific neural circuits. Since Bhlhb5 and Prdm8 belong to conserved gene families,

our finding Proteases inhibitor that these two factors specifically interact raises the question as to whether the functional association between bHLH factors and Prdm-related proteins is a more general occurrence. Phylogenetic analysis of SET-domain containing proteins reveals that Prdm8 is most closely related to Prdm13, and recent studies show that Prdm8 and Prdm13 are expressed in nonoverlapping patterns in the developing nervous system (Fumasoni et al., 2007 and Kinameri et al., 2008). However, we unexpectedly discovered that the gene with which Prdm8 shares the highest degree of similarity (as revealed using a blastn algorithm comparing murine genes) is not a member of the Prdm family, but rather the zinc-finger protein, Zfp488. This Selleck Dactolisib gene shares 82% similarity with Prdm8 over 80 amino acids in the C terminus (Figure 8C), suggesting that Prdm8 and Zfp488 may share a common ancestor. The idea that Prdm8 and Zfp488 are ancestrally related proteins is noteworthy

because Zfp488 was recently shown to interact physically and functionally with one of Bhlhb5′s closest relatives, Olig2 (Wang et al., 2006). This intriguing connection secondly suggests the possibility that the interaction between bHLH transcription factors and Prdm-related proteins is a general mechanism for the regulation of gene expression during neural development (Figure 8B). In this regard, it is notable that both Prdm13 and Olig3 are expressed in Class A progenitors in the dorsal spinal cord, consistent with the idea that these two factors may also couple selectively to mediate transcriptional repression in these cells (Kinameri et al., 2008 and Muller et al., 2005). We provide phenotypic and mechanistic evidence that Bhlhb5 and Prdm8 are obligate partners for certain aspects of development. However, it is likely that Prdm8 functions without Bhlhb5 in some contexts. This prediction is based on the observation that, while Prdm8 shows significant overlap with the Bhlhb5 expression domain, there are regions of the nervous system that express Prdm8 but not Bhlhb5.