Expression and regulation of protocadherin10b in the thalamus.
Lateral views and corresponding cross-sections of the left hemisphere of the same embryo at 48 hpf are displayed. Exceptions are a horizontal section in (c2) and dorsal view in (d). Asterisks mark the thalamic territory. pcdh10b expression abuts the expression domain of lhx9 in the mantle zone (MZ, black bar; a, a2). The roof plate marker, wnt3a, is adjacently expressed to the pcdh10b expression in the thalamus (b, b2). Expression of pcdh10b in the thalamus abuts posteriorly the expression domain of gsx1 and therefore respects the border to the pretecum (c) shown in a dorsal view (c2). Overexpression of lhx2 DNA via electroporation leads to a unilateral downregulation of pcdh10b expression (dorsal view, d; d2). Control embryos show pcdh10b expression in the cTh (d, d2). In lhx2 mutant embryo knocked-down for lhx9, pcdh10b expression expands into the pretectum (e), and the ventricular expression expands into the MZ (e2, white bar). Treatment of embryos with the Wnt signaling agonist BIO from 16 hpf to 48 hpf leads to an expansion of pchd10b expression into the pretectum (f, white arrow), however the expanded VZ is not detectable (f2, white bar). Although the gross morphology is altered, pcdh10b expression shows similar broadening in axin1 mutant embryos (g, g2). Consequently, blocking of Wnt signaling by IWR-1 treatment from 16 hpf to 48 hpf leads to a severe downregulation of pcdh10b (h, h2). Embryos with ubiquitous expression of the Wnt inhibitor Dkk1 after heat shock activation at 10 hpf leads to a downregulation of pcdh10 expression at 48 hpf (i, i2). Knock-down of Wnt3a in the Lhx2/Lhx9-double-deficient embryos leads to a rescue of the expansion into the pretectum (j), however the lateral expansion of the VZ is still detectable (j2). Canonical Wnt signaling—that is, Wnt3a—is required for induction of pcdh10b expression in the thalamic ventricular zone, whereas Lhx2/Lhx9 inhibits pcdh10b expression in the mantle zone of the cTh (k).