Meeting Abstract
P3.93 Monday, Jan. 6 15:30 Expression and Function of Otx during Ciliated Band Development in the Pilidium Larva SWIDER, Z.*; HIEBERT, L.S.; MASLAKOVA, S.A.; VON DASSOW, G.; Oregon Institute of Marine Biology zac.swider@gmail.com
We identified a homolog of orthodenticle, MaOtx, in a transcriptome of the pilidiophoran nemertean Micrura alaskensis. MaOtx is expressed during cleavage in the descendants of 1q2 (primary trochoblasts), 1q12 (accessory trochoblasts in canonical spiralians), and 2q cells (some of which form secondary trochoblasts in other spiralians). In the blastosquare, Otx-expressing cells make an unbroken ring around the perimeter, likely the primordial ciliated band. Otx expression persists in axils – recesses within the primary ciliated band, which are sites of growth and intercalation of new cells into both larval and juvenile bodies. We evaluated MaOtx function using morpholino-mediated knockdown and ectopic expression from injected mRNA. MaOtx morphants gastrulate and make a stomach, esophagus, apical organ and larval epidermis, but fail to develop lappets or a defined ciliated band. Nor do they possess “cone cells”, sense organs embedded within the ciliated band. By the time normal pilidia would have begun to feed and grow, MaOtx morphants have instead begun to seal off their own mouths from the outside world. Phospho-histone labeling showed plenty of dividing cells in morphants, suggesting that it is the differentiation of axillary cells, rather than their proliferation, that is impaired. Overexpression of Otx in all cells led to a superficially similar phenotype to morpholino injection – post-gastrulas had a stomach, esophagus, and apical organ but no defined ciliated band. However, a great excess of cone cells in Otx-injected larvae suggested that ectopic Otx diverts would-be epithelial cells to this fate. We conclude that the normal function of Otx is likely to promote differentiation of various constituents of the primary ciliated band, both in the embryo and during larval growth.
