Wound healing and regenerative response of fragments of the Drosophila wing imaginal disc cultured in vitro

Fragments of imaginal discs of the fruitfly Drosophila undergo growth and pattern regulation when cultured in vivo in adult female hosts for several days prior to metamorphosis in host larvae. Pattern regulation results in either regeneration of excised pattern elements or duplication of elements whose fate map positions lay within the fragment. Initial wound healing along the cut edge of a fragment is thought to be a crucial first step in the process of pattern regulation. We have examined the capacity for wound healing and pattern regulation of fragments (distal halves) of the wing disc cultured in vitro, using the culture system recently reported to support extensive growth and transdetermination of slightly wounded whole imaginal discs in vitro. Our results suggest that disc fragments and whole discs apparently respond differently in the culture system. With disc fragments, wound healing did not occur in vitro. When fragments were first cultured overnight in adult female hosts to allow initial wound healing prior to explantation in vitro, then some volume increase and regeneration of excised portions occurred during 2–3 weeks of culture in vitro. The extent of apparent growth was much less than that reported for whole discs, and the frequency of regeneration in vitro (19%), while highly significant relative to controls not cultured in vitro (0%), was much less than that observed for fragments cultured in vivo (84%). Furthermore the extent of regeneration which occurred in vitro was considerably smaller than that which occurs during regeneration in vivo.