Genetic Control of Cytodifferentiation

Abstract

The cells of the anterior region of the larval fatbody of Drosophila melanogaster accumulate kynurenine at the end of the third larval instar, whereas the cells of the posterior region are involved in pteridine metabolism. Through a series of transplantation experiments it has been demonstrated that the anterior fat cells synthesize kynurenine. The mutant vermilion lacks kynurenine, and the anterior fat cells of this mutant strain lack the autofluorescence characteristic of kynurenine. When the non-allelic suppressor gene is combined with vermilion, the synthesis of kynurenine is restored in the anterior fat cells, and some of the cells of the posterior region contain kynurenine as well. A similar extension in the number of cells containing kynurenine can be induced in the normal Ore-R strain by feeding the precursor tryptophan. It has been concluded that the absence of a physiological process in a differentiated cell does not necessarily represent a loss of the genetic potential for that process. The normal allele at the suppressor locus inhibits the occurrence of kynurenine in the posterior fat cells, whereas the mutant allele su2-s allows the expression of this potential.

Factors Affecting the Intracellualr Synthesis of Kynurenine

“…This pattern of autofluorescence is also maintained when larvae are removed from food in the mid third instar and given only distilled water until they pupate. However, the number of fat cells containing kynurenine is increased when the larvae are fed tryptophan, as reported previously (12). For these earlier studies, L-tryptophan was dissolved in distilled water by slight heating.…”

“…Induction of kynurenine synthesis can also be achieved in Drosophila by feeding tryptophan to the larvae (14). In the latter instance, increased tryptophan pyrrolase activity is correlated with an increase in the number of cells in the fatbody which are producing kynurenine (12). The intracellular distribution of this metabolite in the larval fat cells can be conveniently determined by examination of this tissue with the fluorescence microscope, and it has been shown that the light blue autofluorescence characteristic of kynurenine is limited to the cells in the anterior region of the larval fatbody in the wild-type Ore-R strain of D. melanogaster.…”

AN INDUCIBLE ENZYME SYSTEM IN THE LARVAL CELLS OF DROSOPHILA MELANOGASTER

“…As described previously, "kynurenine cells" are in immediate contact with pteridine cells in the fatbody and diffusion of this metabolite from one region of the fatbody to another does not occur. A dietary supplement of tryptophan increases the quantity of kynurenine in the fatbody and examination with the fluorescence microscope reveals that the fluorescence characteristic of kynurenine is no longer limited to the anterior cells but is found in some posterior cells as well (12,13). It may be questioned whether, under these experimental conditions, the anterior cells produce larger quantities of kynurenine which then diffuse to other fat cells.…”

“…This regional localization of kynurenine synthesis is maintained when the larvae are fed yeast under the usual culture conditions or if the larvae are submitted to a brief period of starvation. Addition of tryptophan to the diet of third instar larvae increases kynurenine production in the fatbody with the result that a greater number of fat cells contain globular cytoplasmic inclusions displaying the characteristic light blue autofluorescence of kynurenine (12,13).…”

Pigments and Color Changes

“…Rizki (136) shows that only the cells of the anterior part of the larval fat body of Drosophila synthesize and accumulate kynurenine. In a normal strain, an extension of the number of cells containing kynurenine can be induced by feeding tryptophan, and cells which are normally differentiated for other synthesis (like pterins) may produce kynurenine as well.…”