Figure 2.

Heterochronic transplanted cells polarize according to their own age rather than the host schedule. (A) Schematic of isochronic and heterochronic cell transplantation strategy. (B) Isochronic transplanted cells integrate into the host neural tube and display the typical morphology of neuroepithelial cells at 24 hours post fertilization (hpf). (C) Green fluorescent protein/polarity protein partitioning defective 3 fusion (Pard3-GFP) is largely cytoplasmic in non-transplanted neural rod cells at 15 hpf, although there are a few small puncta at the developing midline (arrowheads). (D) Pard3-GFP is localized to the midline in non-transplanted neural rod cells at 18 hpf. (E) Isochronic transplanted cells at 15 hpf show Pard3-GFP localization typical of their age (compare to (C)), with some small puncta of Pard3-GFP (arrowheads). (F) Isochronic transplanted cells at 18 hpf show strong midline Pard3-GFP polarization, typical of their age (compare to (D)). (G) Dorsal view of 15 hpf host embryo (green nuclei) containing old (18 hpf) cells (red nuclei). Tissue has been stained for zonula occludens 1 (ZO-1) immunoreactivity (white) revealing high levels of ZO-1 expression adjacent to old cells (bracket) and low levels in regions containing only host cells. White arrows indicate neural midline. Yellow arrow indicates an isolated donor nucleus. (H) Pard3-GFP expression in isolated cells, transplanted isochronically (old into old and young into young) or heterochronically (old into young and young into old). White dots indicate basal surface. Scale bar 20 μm. (I) Quantification of Pard3-GFP polarization in isochronic and heterochronic cells. n, number of cells; ns, not significant; *P <0.01, Fishers test.