Regulation of cell polarity and morphogenesis by Tousled-like kinase in Drosophila. Jenn-Yah Yu, Tsung-Han Yeh, Shu-Yu Huang, Gwo-Jen Liaw. Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan.

   Tousled-like kinase (Tlk) is a conserved Serine/Threonin kinase. It is involved in DNA replication, chromatin assembly, and DNA repair. Interestingly, the expression profile of TLK2, a human tlk homolog, is similar to those of some apical-basal polarity-related genes during cancer progression. Therefore, we test if Tlk plays a role in cell polarity by using Drosophila follicle cells as a model. Forced-expression or knockdown of tlk led to morphological changes in the follicle cells at stage-9 to -10 egg chambers. Some tlk knockdown cells were detached from the apical side, suggesting that tlk is involved in cell polarity and morphogenesis. We further generated tlk mutant follicle cell clones by using the FLP/FRT system and examined the levels and localization of some cell polarity components. A key regulator, aPKC, was increased in tlk mutant cells. Adherens junction proteins Armadillo and DE-cadherin were also increased in the mutant cells. Discs large, a basolateral complex protein, was re-distributed to the apical-lateral region. These results suggest a role of tlk in apical-basal cell polarity. In addition, morphology of the tlk mutant cells was changed from columnar to irregular shape and the filamentous actin was increased in the apical region. In conclusion, we found a novel role of Tlk in regulating epithelial cell polarity and morphogenesis.