Fig. 3

Rescue of cerebellar primordium morphogenesis in gbx-embryos with otx knock-down. Timelapse of embryos during the initial stages of cerebellar morphogenesis. Dorsal views with anterior to the left; genotypes are indicated at the top. Arrowheads indicate the isthmic constriction. (A–E) In WT embryos, inflation of the midbrain (III) and hindbrain (IV) ventricles combined with cell shape changes at the MHB creates a sharp isthmic constriction flanked posteriorly by a thickened bilateral cerebellar primordium (CbP, indicated on the left side with dotted white lines and on the right side by a white bracket indicating thickness). Red lines indicate a 90° rotation of the CbP relative to the more posterior hindbrain epithelium. (H–L) Ventricle inflation is delayed in gbx mutants, the isthmic region is short and no thickened CbP forms. (O–S; V–Z) In otxMO and gbx-;otxMO the isthmic region is extended and a thickened CbP forms. (F, M, T, and AA) The “isthmic region” is where the left and right sides of the neuroepithelium are in contact (white line), and can be easily measured at 22 hpf in WT (F). This region is nearly absent in gbx- (M), but extended in otxMO (T) and gbx-;otxMO (AA). (G, N, U, and BB) atoh1a expression in granule cell progenitors in the upper rhombic lip (URL, black arrows) is lost in gbx- (N) and rescued in both otxMO (U) and gbx-;otxMO (BB).