In our recent paper, Park, M. & Moon, R. T. Nature Cell Biology 4, 20–25 (2002), we reported that modulation of Strabismus levels alters convergent extension movement and the expression pattern of some neural genes. As modulation of other planar cell polarity protein levels in the laboratory (M. Veeman, data not shown), and mutations in strabismus (L. Solnica-Krezel, personal communication) do not result in neural deficits, we have repeated the experiments shown in Fig. 3a.

Based on further injections and staining with additional neural markers, we conclude that overexpression of strabismus in zebrafish embryos results primarily in the inhibition of convergent extension movements, as monitored by abnormal myoD staining, with what are likely to be indirect effects on the expression of neural markers (Fig. 1b versus a, and g versus f).

Figure 1: Effects of Strabismus on neural markers.
figure 1

Lateral (a–e) and dorsal (f–j) views, of injected zebrafish embryos. A representative embryo (lateral (a) and dorsal (f) views) was injected with control green fluorescent protein (GFP) RNA and compared with an embryo injected with strabismus RNA ((b,g) otx-1, arrowhead; myoD, m). An embryo was injected with control morpholino oligonucleotide (c,h) and compared with embryos injected with strabismus morpholino ((d,e,i,j) opl, open arrowhead; engrailed-2, arrow; krox-20, asterisks; and myoD, m).

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With further injections of antisense strabismus morpholinos into embryos, we continue to see examples of reduced anterior neural markers in embryos injected with strabismus morpholinos (Fig. 1e versus c), but most embryos show little effect on neural markers (Fig. 1d versus c). Moreover, further analysis of those individual embryos displaying reduced neural marker staining reveals previously undetected neural cell death. We therefore conclude that the loss of anterior neural markers reported previously was caused by cell death.