Stolen vs. Hydranth Determination in Pennaria Tiarella Planulae: A Role for DNA Synthesis

Lesh-Laurie, Georgia

Larvae of the gymnoblastic hydroid Pennaria tiarella develop and metamorphose in a synchronous and predictable manner. They progress from ovoid pre-planulae 12 hours after fertilization to definitive, filiform planulae by 24 hours of development. Planulae are free living for a defined period of time (approximately 5 days at 21°C) and then metamorphose with the anterior regions of larvae becoming stolons, the posterior regions forming hydranths. The uniformity of this developmental pattern allows the utilization of Pennaria as an experimental system to investigate the principal morphogenetic determination occurring in hydroid larvae, that of stolon versus hydranth. Previous autoradiographic studies (Haynes et al., 1974) revealed regional patterns of 3H-thymidine incorporation during larval development in Pennaria. Early planulae exhibited concentrations of precursor incorporation in the epidermis and posterior portions of the larvae. In later planulae, however, the greatest level of incorporation was reported in the gastrodermis and at the anterior regions of the larvae. Because the autoradiographic observations are consistent with a possible involvement of DNA synthesis and/or mitotic activity in the regional commitment to stolon and hydranth development that occurs in planula larvae, attention was focused on the role of DNA synthesis in this morphogenetic determination. Initially, the kinetics of 3H-thymidine incorporation into DNA in P. tiarella had to be examined to verify the efficacy of this probe to analyze synthetic activity in this organism. Once linearity of incorporation was established, morphological and biochemical events of larval development were compared in unmanipulated planulae, half planulae and planulae exposed to an inhibitor of DNA synthesis (hydroxyurea) or a mitotic blocking agent (colchicine).