Determination and Regulation Capacities of the Wing Disc of the Fleshfly, Sarcophaga peregrina. (wingdisc/determination/fleshfly (savcophaga)/regulation capacity)

Abstract

Unilateral extirpation of the wing discs was performed on mid-and late-third instar larvae of Sarcophaga peregrina to investigate the regulation capacities of the thoracic discs. Out of 636 operated larvae, 175 became adult and all of them exhibited hemithoracic structures, lacking any adult structures in the operated side, which were normally produced from a wing disc. These findings suggest that the wing disc does not possess the capacity of bicentric regulation to produce the thoracic structures of the opposite side.Ample evidence has revealed that the state of determination of imaginal disc cells in Drosophilu establishes succesively through a series of determining steps which lead the disc cells to a stepwise restriction of their developmental capacities. Several authors described that the fragments of imaginal discs in mature larvae implanted into the larval abdomen differentiated into particular adult structures corresponding to the location of the fragment in the disc, as they metamorphosed with the host (1). However, if the discs were cultured in adult female abdomen before the cultivation in the larvae, these fragments made duplicates or regenerates (2, 3). Although formation of duplicates or regenerates was based on regulation capacity existing within a disc, there was a question whether or not such capacity could be extended to regulate the differentiation of adult structures in the opposite side of the thorax, when the animal was dificient in the wing disc on one side. When the wing disc was implanted into mature larva and immediately metamorphosed with the host, no regenerate for duplicate formation was observed (4, 5). ZALOKAR (6) performed total excision of the wing disc and reported that the surviving adult usually possessed a half-mesonotum and one side of the wing (known as the half-thorax or hemithorax fly). The capacites of contralateral regulation between wing discs were first described by WADDINGTON (7). He mentioned that the failure of one mesothoracic bud to evert must lead to regulatory development in the mesothoracic bud of the opposite side in the vg mutant of Drosophilu, and that determination of the form and chaetotaxy of the thoracic rudiment is not complete until some time after the puparium formation. PANTELOURIS and WADDINGTON (8) further investigated this regulation capacity between a pair of wing discs, and reported that in 20 operated flies, 5 specimens were not of the hemithoracic type, but bristles and cuticle of the intact side overgrew to the operated side. Therefore, they speculated that the wing disc possessed a considerable regulation capacity, and that two wing discs are secondarily separated halves of a single median bicentric field.However, MURPHY (9) pointed out with the data obtained from more careful experiments * to whom reprint request should be addressed. 191