Mutant fs(1) 1163 of Drosophila melanogaster alters yolk protein secretion from the fat body

Summary

The mutant fs(1) 1163 of Drosophila melanogaster, which was isolated by Gans et al. (1975) is a recessive homozygous female sterile at 18°C and a dominant female — sterile at 29°C. We reported previously that there are reduced quantities of the largest of the three yolk polypeptides in Drosophila melanogaster in the haemolymph and eggs of this mutant at 29°C (Bownes and Hames 1978 a). In this paper we show that the yolk protein defect maps within approximately 2.5 recombination units of the female sterility at 21±2.5 map units on the X-chromosome. The temperature-sensitive period of the yolk protein defect is after emergence. In vitro labelling of fs(1) 1163 ovaries and fat bodies showed that they were able to synthesise yolk polypeptide 1. Interestingly, studies on the proteins present in the various tissues indicate that the fat body tends to accumulate all three yolk polypeptides in the mutant. This phenotype is partially co-dominant in that an effect is seen in heterozygotes as well as homozygotes and is enhanced by increased temperature. This mutant could therefore have a defect (a) in the structural gene for yolk polypeptide 1, (b) in the processing and secretion enzyme systems; (c) in the fat body or all tissues leading to altered secretion properties.

Mutants like fs(1) 1163 which alter specific steps in vitellogenesis should be of value for analysing the genetic and biochemical control of the synthesis, transport and sequestering of the yolk polypeptides during oogenesis.