Early Event of Sexual Induction in Volvox: Chemical Modification of the Extracellular Matrix

The sexual pheromone of Volvox carter-i elicits drastic changes in the synthesis of extracellular sulfated glycoproteins. Synthesis of at least two sulfated glycoproteins is turned on. Induction of this synthetic capacity is as sensitive to the pheromone (-10-i6M) as the overall process of sexual induction. The earliest response, detectable a few minutes after the application of the pheromone, is the synthesis of a tyrosine sulfate-containing glycoprotein (SG 70). SG 70 is a short-lived molecule (half-life 20 min) and serves as a precursor for an insoluble extracellular matrix structure. The pheromone-induced sulfated glycoproteins described are exclusively synthesized by somatic cells, rather than by reproductive cells, the ultimate recipients of the pheromone’s message. Contrary to earlier reports in the literature, it is demonstrated that isolated reproductive cells remain responsive to the sexual pheromone and develop to sexual spheroids. In the light of this finding together with the site of their synthesis the role of these pheromone-induced glycoproteins is discussed.