Fig. 2. Expression of Grg1, Grg4 and En2 in developing chick tecta. (A) Approximate position of the figures. (B-I) In situ hybridization for Grg4: (B) E4 (stage 22), (C,D) late E5 (stage 28, C at the caudal and D at the rostral), (E,F) E6 (stage 29, E at the caudal and F at the middle, E shows immunohistochemistry with anti-Hu-C/D in red and in situ hybridization for Grg4 in green), (G) late E6 (stage 30), (H) E8 (stage 34) and (I) E14 (stage 40). I' is higher magnification of I. (J-M) In situ hybridization for Grg1: (J) E4 (stage 22), (K) late E6 (stage 30), (L) E8 (stage 34), (M) E14 (stage 40). (N,O) Immunohistochemistry with anti-En2 antibody at late E5 (stage 28; N, caudal; O, rostral). Grg4 is not expressed at late E3 (B). Its expression resumes at late E5 in a gradient along rostrocaudal axis; rostral high (D) and caudal low (C). Grg4 is expressed in the neuroepithelium (NE) and in the Hu-C/D-positive early neuronal layer (*). At late E6.5, Grg4 expression is observed in laminae II and I (F,G). Expression in the ventricular layer (VL) is still observed at stage 40 (I). Grg1 is continuously expressed in the ventricular layer to E14 (J-M). En2 is expressed at late E5 in an opposite gradient to Grg4: caudal high (N) and rostral low (O). Scale bars: 100 µm.