Table 2.

Transected rostral blastoderm isolates (RBIs) tested for Ganf expression with the rostral lower layer intact or removed

Stage of transection
3a/b 3c 3d 4
Lower layer tissues presentH intactH removedH and ADE intactH and ADE removedH and ADE intactH and ADE removedH and ADE intactH and ADE removed
Numbers of isolates11/192/175/194/157/123/157/120/8
  • H, hypoblast; ADE, anterior definitive endoderm.

    Type B RBIs cultured in collagen and probed for Ganf expression. At each stage, control transections were performed with the lower layer remaining intact in RBIs. RBIs with the lower layer removed are shown on the right. Central epiblast (CE) is present in stage 3a/b RBIs; lower layer is hypoblast only. Removing hypoblast dramatically reduces RBIs with Ganf expression. At stage 3c, RBIs exclude CE and ADE is not fully specified. Removal of the lower layer has no affect on Ganf expression in the few neuralised RBIs. At stage 3d/4, exclusion of CE has no effect as neural specification has occurred. Removal of the hypoblast and specified ADE results in a reduction of Ganf expression in RBIs.