Figure 6.
HCN4 helps coordinate the distribution of Xenopus nodal-related 1 (Xnr-1) expression. (A) During normal development, Xnr-1 is expressed exclusively in the left lateral plate mesoderm following the completion of neurulation as seen via in situ hybridization (NF stage 21, i). Both overexpression and injection of HCN4-DN(AAA) resulted in bilateral expression of Xnr-1, with the secondary Xnr-1 field ranging from a small partial field containing few cells (yellow arrow, iii) to an equivalent right-sided field (white arrow, ii). In addition to generating a second field of Xnr-1, punctate dots of expression were observed along the fused neural tube (iii, red arrow) and flanks of embryos. These ectopic dots were found on both sides of embryos regardless of the presence of endogenous Xnr-1 expression. Dorsal views, anterior at top. (B) While abnormal (bilateral, punctate, and right-sided reversed) expression was observed in all injection conditions, only HCN4-DN(AAA) injection caused a significant increase in abnormal phenotypes compared with uninjected embryos (χ2 = 31.0207, df = 4, *p < 0.05). n = 73–84 per condition across 3 biological replicates. OE = HCN4-OE, DN = HCN4-DN(AAA). Scale bars = 200 μm.