Hereditary sensory and autonomic neuropathy type II (HSANII) is an early-onset autosomal recessive disorder characterized by loss of perception to pain, touch, and heat due to a loss of peripheral sensory nerves. Mutations in hereditary sensory neuropathy type II (HSN2), a single-exon ORF originally identified in affected families in Quebec and Newfoundland, Canada, were found to cause HSANII. We report here that HSN2 is a nervous system-specific exon of the with-no-lysine(K)-1 (WNK1) gene. WNK1 mutations have previously been reported to cause pseudohypoaldosteronism type II but have not been studied in the nervous system. Given the high degree of conservation of WNK1 between mice and humans, we characterized the structure and expression patterns of this isoform in mice. Immunodetections indicated that this Wnk1/Hsn2 isoform was expressed in sensory components of the peripheral nervous system and CNS associated with relaying sensory and nociceptive signals, including satellite cells, Schwann cells, and sensory neurons. We also demonstrate that the novel protein product of Wnk1/Hsn2 was more abundant in sensory neurons than motor neurons. The characteristics of WNK1/HSN2 point to a possible role for this gene in the peripheral sensory perception deficits characterizing HSANII.

Retinoic acid (RA) is required for diverse developmental programs, including vertebral specification. Both RA receptor disruption and excess RA result in homeotic transformations of the axial skeleton. These effects are believed to occur through altered expression of Hox genes, several of which have been demonstrated to be direct RA targets. Members of the cdx (caudal) homeobox gene family are also implicated in regulating Hox expression. Disruption of cdx1 results in vertebral homeotic transformations and alteration of Hox expression boundaries; similar homeosis is also observed in cdx2 heterozygotes. In Xenopus, gain or loss of Cdx function affects vertebral morphogenesis through a mechanism that also correlates with altered Hox expression. Taken together with the finding of putative Cdx binding motifs in several Hox promoters, these data strongly support a role for Cdx members in direct regulation of expression of at least some Hox genes. Most retinoid-responsive Hox genes have not been demonstrated to be direct RA targets, suggesting that intermediaries are involved. Based on these findings, we hypothesized that one or more cdx members may transduce the effects of RA on Hox transcription. Consistent with this, we present evidence that cdx1 is a direct RA target gene, suggesting an additional pathway for retinoid-dependent vertebral specification.

The Cdx1 gene product is essential for normal anterior-posterior vertebral patterning. Expression of Cdx1 is regulated by several pathways implicated in anterior-posterior patterning events, including retinoid and Wnt signaling. We have previously shown that retinoic acid plays a key role in early stages of Cdx1 expression at embryonic day 7.5 (E7.5), while both Wnt3a signaling and an autoregulatory loop, dependent on Cdx1 itself, are involved in later stages of expression (E8.5 to E9.5). This autoregulation is reflected by the ability of Cdx1 to affect expression from proximal Cdx1 promoter sequences in tissue culture. However, this region is devoid of a demonstrable Cdx response element(s). We have now found that Cdx1 and LEF1, a nuclear effector of Wnt signaling, synergize to induce expression from the Cdx1 promoter through previously documented LEF/T-cell factor response elements. We also found a direct physical interaction between the homeodomain of Cdx1 and the B box of LEF1, suggesting a basis for this synergy. Consistent with these observations, analysis of Cdx1 Wnt3a vt compound mutants demonstrated that Wnt and Cdx1 converged on Cdx1 expression and vertebral patterning in vivo. Further data suggest that Cdx-high-mobility group box interactions might be involved in a number of additional pathways.