Models of pattern formation in insect oocytes.

Pattern formation in early insect development is dominated by coordination of the germ lines polarity with the polarity of the follicle cell layer. The production of an elaborate protective chorion, covering the ovulated oocyte, has made establishing parallel polarity of germ line and soma absolutely essential. Genetics and molecular biology, particularly on Drosophila melanogaster, have identified numerous signals passed from follicle cell to oocyte and vice versa. The physiological basis of this communication is beginning to be established with the identification of several membrane receptors and potential signal transduction steps. The contributions of three physiological models of pattern formation are discussed as they relate to the growing genetic model. Evidence for and against ionic currents as factors in polarity determinations is particularly emphasized.