Evolution of Development in Tardigrades (Water Bears)

I began studying tardigrade development as a side project soon after setting up my lab at UNC in 1999. My initial goal was to explore whether tardigrades could be a useful model for studying the evolution of development. This goal was sparked by the discovery in the late 1990's that C. elegans and Drosophila are much more closely related to each other than previously expected, both members of the Ecdysozoa^[1]. We postulated that phyla closely related to these two models could become valuable evo-devo models, if organisms with a set of useful characteristics for study in the lab could be found. Our work on water bear development is summarized on our tardigrades web site.

Cell interactions can change the fates of large groups of cells.  In recent years, it has become clear that developmental cell interactions can also polarize single cells.  Such polarization events often depend on Wnt signals, important players in both development and cancer cell biology.  It has not been clear whether Wnt signals truly act as asymmetric cues that polarize cells, or, alternatively, whether Wnt signals simply must be present while other signals polarize cells.  For example, expressing Wnts in worms either ubiquitously or in an abnormal position can rescue normal Wnt-dependent cell polarity (Herman et al 1995, Whangbo et al 2000) -- suggesting that the asymmetric presentation of the Wnt signal could be unimportant, at least in some cases of cell polarization.  Planar cell polarity in Drosophila can be reoriented by repositioning the transmembrane receptor frizzled, but a Wnt ligand has not been identified for planar cell polarity (Adler, 2002).  I have investigated this issue by placing cells bearing Wnt or other signals at specific positions on individual responding cells, using direct manipulations of cells from wild-type and mutant C. elegans embryos.