-- JHB
Daniel H. Shain
Assistant Professor
Rutgers University
Department of Biology
Science Building
315 Penn St.
Camden, NJ 08102
(856) 225-6590
[EMAIL PROTECTED]
Molecular and cellular development of annelids
Leeches are often viewed with a mixture of horror and disgust, but their embryos are quite beautiful and provide a particularly favorable system for examining questions in development and evolution. Leech embryos are large, robust, and they develop rapidly (from egg to juvenile in about three days). Early embryogenesis in leech is characterized by stereotypical cleavages, which permits the identification and microinjection of specific cell lineages. In addition, the leech genome is small which facilitates the analysis of gene function. We are applying modern molecular techniques to clone and examine the function of numerous developmentally associated genes. These range from maternal mRNAs to genes associated with neuronal differentiation. Our cloning strategies have been to isolate leech homologues by degenerate PCR, and to identify novel genes by Differential Display. Genes are then misexpressed in developing leech embryos by microinjecting plasmid constructs or RNA (for overexpression or RNA, respectively).
Ice worms occupy a unique niche in metazoan phylogeny in that they are one of only a few animals that complete their life cycle in ice. Although they are closely related to leeches phylogenetically, ice worms are confined geographically to western coastal glaciers of North America. Among the curious behaviors of ice worms is their remarkable ability to penetrate hard glacial ice. To address this and other questions, we have examined peculiarities of ice worm morphology by scanning and transmission electron microscopy (SEM and TEM). We find that ice worms have a number of unusual structures including a large head pore at the tip of their head,differentially-oriented setae that curve abruptly at their distal end, and an abundance of sensory organs at their anterior end. It is likely that some or all of these structures have contributed to the ice worm's ability to survive in a glacial environment. We are most interested in how ice worms develop at 0šC since the cellular and metabolic processes of most other animals cease at this temperature. As a first step, we are cloning candidate ice worm genes that are likely to be modified for cold-temperature survival (e.g., tubulin, polymerases). The National Geographic Society has recently supported our efforts by funding an expedition to Alaskan glaciers to study ice worms in their natural habitat. We hope to document their distribution, daily migrations, reproductive behaviors and their early embryonic development in the near future.
