Fig. 1.

Whole mount in situ hybridization indicating embryonic expression of β4.1 and β4.2. To minimize cross-reactivity between the two genes, antisense probes were designed to regions of 3′ untranslated sequence not significantly conserved between the β4.1 and β4.2 loci. A–D: at 18 hours postfertilization (hpf), expression occurs in the spinal cord (sc), forebrain (fb), midbrain (mb), hindbrain (hb), and yolk syncytial layer (ysl). Insets in A and C show dorsal views of the cardiac cone. In A, inset, β4.1 is not expressed strongly in the cardiac cone (arrowhead), prior to heart tube elongation, whereas (C, inset) strong β4.2 expression is detected in the heart (ht). E, F: central nervous system expression in the trunk decreases by 24 hpf. G, H, K, L, M, N: widespread but differential expression is detected in the brain at 32–36 hpf, specifically in the diencephalon (di) and telencephalon (tel), tegmentum (teg), cerebellum (ce), midbrain-hindbrain boundary (mhb), and the hindbrain. I, J: sense probes (negative controls) for β4.1 and β4.2, respectively, produced no signal. O, R: cardiac expression in 48 hpf embryos was primarily limited to the atrium (a). P, S: for comparison, sodium calcium exchanger, heart (NCX1h) expression occurs in both chambers, whereas ventricle myosin heavy chain (vmhc) expression is limited to the ventricle. U–Y: at 72 hpf, embryos express β4.1 in the pharyngeal arches (pa), including the mandibular arch (m) and ethmoid plate (ep), β4.2 in the habenular nuclei (ha), and both genes in the retina (r).