The Development of Gastric Tumours in Drosophila Larvae

Abstract

ABSTRACT A sex-linked factor in Drosophila, lethal-no-imaginal-buds (1-nib) produces two main effects: reduction, or even complete absence of the imaginal buds; and excessive proliferation of the epithelium of the stomach, leading to occlusion of the gut and death from starvation. The intensity with which these two effects are expressed varies independently in different stocks. This paper is primarily concerned with the formation of the gastric tumour. The first pair of lymph glands, after their breakdown in the later part of the first instar, usually regenerate only incompletely. With increasing abnormality of the glands, there was an increasing tendency for excessive proliferation, or for cellular degeneration, in the testes, hind-gut primordia, and stomach, in that order. In severely affected larvae, the lymph glands degenerate at the end of the second instar. This is followed by, and is thought to be the cause of, a strong hypertrophy of the gastric epithelium, which leads to the filling up of the gut lumen with cells and anuclear cytoplasmic masses. It is probable that a preliminary stage in the development of this hypertrophy is the proliferation of the cells of the mid-gut imaginal primordia. Similar proliferation and/or hypertrophy occurs in the hind-gut and salivary gland primordia. The cells of all these proliferations eventually undergo degenerative processes involving the deposition of melanin, when they become converted into melanotic ‘tumours’. These are usually anchored to their places of origin, in contrast to the free tumours found in some other Drosophila stocks. Preliminary experiments indicate that the development of the proliferations can be suppressed by the injection of normal lymph glands into early third instar larvae. In individuals from which the cephalic buds are missing, there is no development of the optic glomeruli in the brain. In the stock lethal-malignant (Shatoury, 1955) the lymph glands undergo pathological changes of a different type; they become excessively hypertrophied in the late third instar, and develop into a metastasizing tumour which eventually undergoes various degenerative changes. In this stock also the gastric epithelium begins to exhibit excessive hypertrophy at the same time as the lymph glands become abnormal. A full gastric tumour may develop; in this case the basement cells are involved in addition to the main epithelium. It is suggested that the complex interrelations between the lymph glands, the migratory cells given off from them (oikocytes), and the apparently hormonally controlled proliferative tendencies of tissues such as the gastric epithelium, constitute a novel type of epigenetic system, which may be special to the larvae of holometabolous insects or even of Drosophila alone.