Positional information and gonadal differentiation in the planarian Dugesia lugubris (Turbellaria)

Abstract

The planarian Dugesia lugubris is a balanced hermaphrodite, meaning that male genetic factors are in equilibrium with female factors. Differentiation of the gonads is controlled by the region in which they develop. According to the classical theory of germ cell formation, these cells stem from neoblasts that are induced to differentiate by factors specific to the gonadal regions, factors presumably due to gradients formed by neurosecretory activity of the cephalic ganglia and longitudinal nerve cords. A more recently proposed theory holds that germ cells in regenerates originate not from neoblasts but from dedifferentiated cells and that characteristics of the gonadal regions are determined by direct interactions of cells here. Results of our experiments with homo- and autoplastic grafst support the classical theory. Prepharyngeal portions grafted onto posterior body portions retained their ability to maintain or induce development of ovaries. Post- pharyngeal portions grafted onto anterior portions produced only testes even though the brain developed normally in these regenerates. Under these experimental conditions, gonad regeneration took longer than it does in normal regeneration (i.e., that in which body regions are not displaced).