Meeting Abstract

P3.108  Sunday, Jan. 6  How the pilidium larva grows BIRD, AM; VON DASSOW, G; MASLAKOVA, SA*; Oregon Institute of Marine Biology, Univ. of Oregon svetlana@uoregon.edu

Many benthic marine invertebrates have ciliated planktonic larvae which must feed and grow in order to reach metamorphosis. The fact that ciliated cells in animals are apparently unable to divide while in possession of a cilium implies possible constraints on how ciliated larvae can grow. Monociliated cells may lose their cilium, divide, and regrow the cilium, but cells that develop multiple cilia can no longer divide. The planktotrophic pilidium larva of nemertean worms grows considerably during its long pelagic life (weeks to months), and its overall size and the length of its ciliary bands has likely consequences for its feeding efficiency. The epidermis of the pilidium consists of multiciliated cells. Do these cells simply stretch to accommodate an increase in size, or are there non-ciliated or monociliated cells that contribute to the growing larval body? By using an anti-phosphohistone antibody, BrdU labeling and confocal microscopy, we detected dividing cells in the pilidium of Micrura alaskensis. They are restricted to several discrete regions of the larval body, most notably in the pits between the larval lobes and lappets. We refer to these regions as “axils” (Latin “pits”). We show with BrdU pulse-chase that proliferating cells in the axils contribute both to the larval body (including the ciliary band), as well as the imaginal discs from which the juvenile worm develops. We also located the putative growth zones in the pilidial axils by scanning electron microscopy – the cells in the growth zones are smaller than the neighboring cells, and have a single rudimentary cilium each, as opposed to multiple well-developed cilia. These findings not only illustrate how this multiciliated body can grow, they also suggest a mechanism by which growth of larval and juvenile bodies could be coupled.