Pleiotropic effects in the four jointed mutant of Drosophila melanogaster.

Abstract

Studies of the adult morphology of male D. melanogaster suggest that a shortening of body parts is the common aspect of the pleiotropic effects of fj (four jointed tarsi) on the development of the leg, wing, scutellum, distal parts of antenna, and one of three tergite segments measured. In the scutellum and distal antenna the only detected effect of fj is overall shortening, whereas local effects appear in leg and wing. Shortening of the leg is maximal (44%) at the proximal tarsal segments and absent at the distal two, confirming earlier studies. In the wing, total length is reduced 10% and maximum shortening (50%) occurs in the area between the anterior (ACV) and posterior (PCV) cross veins, while the proximal longitudinal veins are longer or unchanged. The effect of fj on wing width is small. Observations on cell density and bristle spacing also indicate that the strongest effect of fj is in the central area, between the ACV and PCV. We interpret the primary effect of fj to be a general reduction in the longitudinal growth pattern of many different imaginal discs. Secondary effects in the leg include a change in tarsal segmentation, followed by a bristle pattern change. In the wing, the angle of veins, bristle pattern on the subcosta vein, positions of ACV and PCV, and cell density variations are secondary effect of fj. A decrease in cell density on the wing surface between ACV and PCV may be related to a final stretching of wing tissue after the process of vein formation. Local effects are not seen in other discs which lack sequential regional patterning mechanisms emphasizing the effects of general shortening. The similarities in developmental aspects between leg and wing are discussed in relation to homoeotic changes by certain mutants.