Exploring germ-soma differentiation in Volvox

As we sat at the bowrail sipping Bloody Marys in the early morning fog 30 years ago, we had the feeling of being suspended in space and time. With the engines of the Delta Queen – the last authentic sternwheeler on the Mississippi river – working at full throttle, the downstream rush of the fall flood waters was so powerful that our upstream movement was barely perceptible. We had planned this trip months earlier, just as a weekend immersion in river nostalgia. But the timing turned out to be perfect: it provided us three days away from ringing telephones and fretting students, and a wonderful opportunity to discuss our long-range scientific goals in a leisurely manner, and to decide which path to take at the fork in the road that we had now reached. For several years we had been frustrated by our limited ability to address fundamental issues of cellular determination and development in the avian and mammalian models with which we had been working, distressed by the competitiveness and rancor within the particular branch of developmental biology in which we found ourselves, and anxious to identify more rewarding alternatives. With that mindset, we had spent several periods at Stanford’s Hopkins Marine Station with Don Abbott, an enthusiastic and exceptionally knowledgeable invertebrate zoologist, looking for interesting and accessible new “developmental models” in the intertidal zone. Although we had identified candidate organisms that we could keep indefinitely in artificial-salt water aquaria at Hopkins, every attempt to keep them alive more than briefly in St. Louis aquaria had failed. So we had turned our attention (somewhat ruefully) to organisms that were less averse to living in the US heartland. Germ-soma specification and differentiation had long interested us, and at that time Drosophila, with its existing stock of grandchildless mutants, appeared to provide the most promising avenue for elucidating the genetic and molecular basis of germ cell determination. Because all offspring of a homozygous grandchildless mother lack germ cells, we assumed that the wild-type allele of grandchildless probably encoded an essential component of the polar plasm, which had been shown to be capable of triggering germ cell formation (Ilmensee and Mahowald 1974). Therefore, we had been on the verge of applying for the opportunity (and the funds) to spend a sabbatical year in Switzerland with Walter Gehring, to begin studying fruit fly germ-cell biology. Just as we were about to start writing those proposals, however, Richard Starr visited our department to talk about an organism we had last heard of in high school biology class: Volvox. Although leading biologists had been fascinated by Volvox since 1700, the first person to succeed in keeping any species of Volvox alive in the laboratory for more than a few weeks was one of Starr’s first doctoral students, Bill Darden (1965). That breakthrough had so fired Starr’s imagination that he had promptly circled the globe to bring into continuous culture, and study, all 18 known and several previously unknown species of Volvox. His seminar focused on asexual and sexual development in a male-female pair of V. carteri forma nagariensis Iyengar strains that he had isolated from a pond in Japan in 1967, and that he subsequently found had “an unusual combination of characteristics” that made them particularly suitable for developmental genetic studies (Starr 1970). The beautiful time-lapse movies of V. carteri development that he had projected, and the fascinating developmental mutants that he had described, were still fresh in our minds as we boarded the Delta Queen. Thus, our major preoccupation as we headed upstream was enumerating the pros and cons of Volvox vs Drosophila Perspectives