I am interested in how simple animals transduce mechanical stimuli into physiological responses. The research currently is divided into two projects. One project concerns how sea anemones "hear" vibrations. Anemones have mechanoreceptors called hair bundles covering the surfaces of their tentacles. The hair bundles are composed of actin-based sterecilia arising from a multicellular complex. A central senory neuron surrounded by hair cells comprise the complex. Using electrophysiology and functional imaging of intact tentacles, we investigate the mechanisms involved in detecting mechanical stimuli by the hair cells and the communication pathways used to convey the information between cells of the complex. We find that hair cells in anemones function similarly to hair cells in hearing organs of higher animals but also exhibit some interesting differences. The differences include multidirectional sensitivity, complete adaptation to prolonged stimulation, habituation to repetitive stimuli, and modulation by activated chemoreceptors. Ongoing experiments involve teasing out the mechanisms resposnsible for these unique attributes using patch-clamp techniques combined with pharmacology and computer-based microscopy. The other project concerns the cellular regulation of asexual reproduction in anemones, with an emphasis on mechanically induced events. Anemones divide periodically by longitudinal fission, a violent process with distinct stages. Using timelapse video microscopy, we find that fission begins with stretching of the animal in two directions, then enters a "tug-of-war" phase during which tissue in the center of the animal thins, and ends with tearing of the animal into two parts. We find that fission is triggered by applying mild stretch to nondividing animals and is inhibited by gadolinium in dividing animals. These results indicate that stretch, likely involving stretch-gated ion channels, serves as a mechanical stimulus to cause progression of the fission program. Furthermore, we find that programmed cell death (apoptosis) occurs in specific spatio-temporal patterns during fission. Apoptosis is induced in stretched tissues specifically. Ongoing efforts are targeted at determining the structural and molecular players involved in linking the mechanical stimulus to specific fission events with a focus on the induction of apoptosis. We use in situ TUNEL cytochemistry, immunohistochemistry, biochemistry, TEM, pharmacology, and whole animal studies to address these questions.

• Mire, P. and G.M. Watson 1997 Mechanotransduction of hair bundles arising from multicellular complexes in anemones. Hear. Res. 113:224-234.
• Mire, P. 1998 Evidence for stretch-regulation of fission in a sea anemone. J. Exp. Zool. 282:344-359.
• G.M. Watson and P. Mire 1999 A comparison of hair bundle mechanoreceptors in sea anemones and vertebrate systems. Curr. Topics Dev. Biol. 43:51-84.