Growth and degeneration of the larval abdominal epidermis in Calliphora erythrocephala (meig.) (Diptera: Calliphoridae) during larval life and metamorphosis

Programmed cell death during metamorphosis in the blow-fly Calliphora vomitoria

During metamorphosis, the salivary glands of the blow-fly undergo programmed cell death. Data is presented indicating that this programmed cell death does not in many respects emulate classical apoptosis. The cells are seen to vacuolate and swell rather than condense and shrink. There appears to be a transient enhancement in autophagy and an increase in acid phosphatase activity. This is followed by the characteristic appearance of ribosomal and extracisternal sources of the enzyme leading to autolysis. There appears to be no lysosomal leakage of acid phosphatase. As in apoptosis, the mitochondria persist until the cell fragments. The nucleus, however, does not show the distinct chromatin margination and blebbing that is typical of apoptosis. These changes are compared with necrotic changes induced by experimental anoxia. Overall the results show that a programmed cell death distinct from classical apoptosis is taking place.

Pattern regulation in the ventral histoblasts of the housefly: induction of sternal pattern abnormalities by mechanical wounding of larval epidermal cells

In higher Diptera, two nests of diploid cells called the ventral histoblasts, located one on either side of each abdominal segment among the polytene larval epidermal cells, give rise to the sternite and its surrounding pleura. During metamorphosis of the insect, these two groups of cells migrate and meet with each other in the midventral region of the developing adult. The cuticular pattern elements and pigmentation in the fifth sternite of the male housefly, when compared to those of other segments as well as the tergites of both sexes, are quite distinct. The above-mentioned features, coupled with the smaller number and predictable occurrence of one of the pattern elements in this sternite, viz, the primary forceps, help one to determine the developmental potential of the histoblast nest and the regulation of its potential which occur at the time of fusion of the two contralateral nests of this segment. A simple operation of slitting the larval epidermal cells (LEC) in a hemisegment in the vicinity of the histoblast nest or extirpation or rotation of a small rectangular piece of LEC between the ventral nest and the midventral line produced pattern abnormalities including mirror image duplication in the hemisternite. An analysis of these pattern abnormalities in the different segments and, in particular, in the fifth segment provides a dynamic picture of the formation of the median sternite. Further, these abnormalities indicate the significance of the presence of the intervening pleural cells between the confronting hemisternites under experimental conditions. Thus, each of the fifth ventral nests has the developmental potential to form more than half of the final sternite pattern. Possible mechanisms for the formation of the normal median sternite during metamorphosis and for the formation of duplicated hemisternites and their fusion products under experimental conditions are discussed in light of current models of pattern regulation.