Fig. 2. HTL is required for the attachment of the mesoderm to the ectoderm. Embryos (stage 7; phase 1 of migration) were fixed and stained with anti-NRT (red) and anti-TWI (green) antibodies (A,C) or with anti-CD2 antibodies (B,D). (A) In the wild type, the mesodermal tube is attached to those ectodermal cells that lie adjacent to the basal cells of the tube (arrowheads). (B) The invaginated mesoderm cells are aligned along the midline of the embryo, indicated with arrowheads. (C) In embryos homozygously mutant for htl^AB42, the basal cells of the mesodermal tube fail to adhere to the ectoderm. (D) Misalignment of mesoderm cells in htl mutants with respect to the ventral midline (arrowheads in B,D). (B,D) Projections of a stack of confocal images covering a total of 25 µm from the ventral surface of the embryo to the interior.