STUDIES ON THE EXPRESSION OF THE TRANSFORMER GENE OF DROSOPHILA MELANOGASTER

Abstract

TURTEVANT's transformer gene (tra) of Drosophila melanogaster is a third Schromosomal recessive which has no effect on males but converts homozygous females into flies which resemble normal males. These transformed females show malelike abdominal tergites, anal plates, external genitalia, and the typical male abdominal coloration. Transformed females possess male sex combs, and dissec-tion reveals normal male genital ducts, accessory glands and an ejaculatory bulb. The testes, however, while showing the characteristic yellow pigmentation of the sheath and the normal attachment to the ejaculatory duct, are greatly reduced in size and fail to develop the usual coiled condidon. Although these "males" mate with females, their testes fail to develop sperm, and they are thus completely sterile. STURTEVANT (1945) pointed out two ways in which XX tra/tra individuals resemble normal females; they are generally larger than males and are found more often in young than in older cultures (as are normal females which have a slightly shorter developmental period than males). STURTEVANT located the tra gene in chromosome I11 between scarlet (44.0) and clipped (45.3). By suitable crosses STURTEVANT transferred the gene to an attached-X stock and found the X%Y tra/tra individuals to be phenotypically identical to flies of genotype XX traltra. Thus, the Y chromosome is without effect upon the action of tra. MULLER (1955) found XXYY tra/tra individuals (containing two Ys.X.YL chromosomes) to be sterile, and XY tra/tra individuals (containing one Ys. X,YL chromosome) to be fertile. Thus, the sterility of transformed females cannot be due to insufficient doses of Y chromosomal fertility factors or to the presence of a third chromosomal recessive gene which causes male sterility when homozygous. NOVITSKI (1951) synthesized a stock carrying "transformer" and an unstable ring X chromosome (XcZ, Zn(l)wvc), which is frequently lost during early cleavage. The loss of the ring X produces XXY tra/tra mosaics which contain large patches of XY tra/tra tissue. Of the fertile mosaics (8 out of 24) none produced female offspring carrying the ring X chromosome. This finding indicates that the testes of the fertile "male" mosaics were composed, at least in part, of cells having the XY AA constitution characteristic of normal males, and only these cells underwent normal spermatogenesis. STURTEVANT also established a triploid stock carrying transformer, and XXX tra/tra/tra individuals were found to resemble the diploid transformed females,