Most peb¹¹⁴²/y embryos do not successfully complete germ band retraction.

Mutant embryos do not retract their germband during stage 13. In mutants embryos the early aspects of tracheal cell fate specification and morphogenesis are indistinguishable from wild-type. During stages 14 and 15, mutant embryos exhibit several tracheal defects, foremost of which is the constriction and expansion of the dorsal trunk to form sac-like structures. Similar defects are seen in the smaller tracheal branches which collapse and become misshapen. By stage 16 many sacs have pinched off and tubes no longer connect these sacs. the lumen is no longer continuous and secondary branching does not occur. Tracheal defects are most severe in the posterior region of the embryo. The tracheal epithelium in peb¹¹⁴² mutant embryos has ultrastructurally normal zonula adherentes that are present apicolaterally as in wild-type. Regions of the trachea are either collapsed or expanded compared with wild-type and in places the lumen is severely reduced in size. There are no obvious defects in either the polarity or the general cytological organisation of the surviving tracheal cells in peb¹¹⁴² mutants either prior to or during loss of normal epithelial architecture. In peb¹¹⁴² mutant trachae the epicuticle is secreted but there are no taenidial folds in either the collapsed or the expanded regions.