A small but significant proportion of step^KG09493/step^k08110 transheterozygous embryos exhibit lethality, and a large proportion of these also exhibit epidermal defects, including head scars and a "head hole" phenotype. Prior to germband retraction, these mutants display an apparently normal columnar epithelium and apparently normal mitotic domains that expand the epidermal cell population. During germband retraction in these mutants, a large proportion of epidermal cells exhibit apical elongation, while the non-apical elongating cells are frequently clustered in long-lived rosette-like structures, as compared to controls; laser ablation of either myosin cables (labeled by fluorescent Zipper) of adherens junctions (labeled by fluorescent E-Cadherin) in these epidermal cells leads to significantly faster instantaneous recoils than in controls. During mid-dorsal closure in these mutants, the pulsatile actomyosin networks in amnioserosa cells are indistinguishable from controls.

During mid-dorsal closure, step^KG09493/Df(2L)BSC150 and step^k08110/Df(2L)BSC150 transheterozygous embryos exhibit a significant increase in the leading-edge cell contact lengths and a frequent clustering in long-lived multi-cellular rosettes, as compared to controls; step^KG09493/Df(2L)BSC150 also exhibit a significant decrease in the aspect ratios of the apicolateral circumference of the rear cells, as compared to controls.