Figure 4.

Biased migration of melanocytes along the left-right axis. (a) Xenopus embryos at stage 30 analyzed by in situ hybridization for melanocyte marker trp2 show a higher number of melanocytes on the left side (i) as compared to the right side (ii) of the embryo. Red arrowheads indicate the melanocytes being counted. (b) Quantification of a number of stage 30 embryos showing biased trp2 spots indicates that 78.6% of embryos show a leftward bias of trp2 staining. 21.4% of embryos showed higher trp2 staining on the right side. The data were analyzed using a two-tailed Binomial calculation; n = 28. (See Table 1 for details). (c) Quantification of Xenopus embryos at stage 26 analyzed by in situ hybridization for trp2 shows no asymmetry in melanocyte number prior to their migration. Due to dense staining at this early stage individual stained cells could not be resolved and counted, hence the stained region was marked, and the area was quantified. Quantification of the trp2 stain on the left and right sides of embryos (n = 10) shows no significant difference in the staining. The areas of the signal on right and left sides were compared using a t-test. (d) Transverse agarose sections of in situ hybridized Xenopus embryo at stage 26 showing left-right distribution of the melanocyte marker trp2 as measured. Illustration shows the plane of sectioning of the stage 26 embryo. Symmetric trp2 expression (red arrowheads) is found in the area around the neural tube. Scale bar = 200 μ.