Fig. 1. L-R asymmetric development and gene expression in developing gonads of chick. (A,B) The number of cortical and medullary cells was determined as described (see Materials and methods and Fig. S2E,F in the supplementary material). The relative fold changes in the number of cortical (A) and medullary (B) cells are plotted, with the numbers in the right cortex and right medulla of the female gonad at stage 27 set at 1. (C-F) Cell proliferation was examined at stage 27 (C) and stage 29 (D). The developing gonads in BrdU-labeled embryos were sectioned and subjected to immunostaining for BrdU (green) and cytokeratin (red) (C,D). Relative fold changes in the number of BrdU-positive cells in the gonadal cortex and medulla are plotted, with the numbers in the right cortex (E) and right medulla (F) of the female gonad at stage 27 set at 1. (G-L) The expression of RALDH2 (G), CYP26A1 (H), RAR (I), PITX2c (J), Ad4BP/SF-1 (K) and LHX9 (L) in the embryonic gonad at stage 27 was examined in both sexes by whole-mount in situ hybridization. Sections of female (ZW) gonads are shown. R and L indicate right and left, respectively. ZW and ZZ indicate female and male, respectively. Scale bars: 100 µm.