Pheromone-Binding and Matrix-Mediated Events in Sexual Induction of Volvox carteri

A Gender-Specific Retinoblastoma-Related Protein inVolvox carteriImplies a Role for the Retinoblastoma Protein Family in Sexual Development

“…The evolution of multicellularity also involved a change in the mode of sexual reproduction from isogamy (as found, for example, in C. reinhardtii ), which involves gametes of the same size, to oogamy (as found, for example, in V. carteri ), in which the nonmotile female gamete (egg) is significantly larger than the motile male gamete (sperm). In V. carteri, sexual development of both males and females is triggered by a sexinducer glycoprotein at concentrations as low as 10 216 M (Starr, 1970;Starr and Jaenicke, 1974;Gilles et al, 1984;Tschochner et al, 1987). The consequences of the evolutionary switch to oogamy for the RB pathway are thus far unknown.…”

Early event of sexual induction in Volvox: Chemical modification of the extracellular matrix

“…In this respect, it is of considerable interest whether isolated gonidia still respond to the sexual pheromone and develop sexual individuals. It has repeatedly been stated in the literature (Gilles et al, 1984;Jaenicke, 1979) that this is not the case, without, however, any presentation of experimental conditions. We therefore reinvestigated the pheromone's action on gonidia in isolation under a number of different experimental conditions.…”

“…This model predicts that isolated free gonidia will not respond to the pheromone because they lack the essential signal transducing system provided by the extracellular matrix. It has repeatedly been reported in the literature (e.g., Gilles et al, 1984) that gonidia in isolation indeed will not respond to the pheromone, even though they remain healthy and capable of normal asexual development. In our hands, however, up to 100% of a population of isolated gonidia reproducibly initiated sexual development in the presence of pheromone.…”

The sexual inducer of Volvox carteri Primary structure deduced from cDNA sequence

“…The inducer is one of the most potent biological effector molecules known as it exhibits full effectiveness at about lo-l6 M [2,7]. Only recently has it become possible to purify this inducer in sufficiently large amounts to obtain amino acid sequence data and to identify the inducer gene [8].…”