C-terminal kinase domain of Drosophila Four-jointed (Fj), mouse Fjx1, and related proteins
Drosophila Fj is a Golgi type II transmembrane protein that is partially secreted, and is a kinase that phosphorylates Ser or Thr residues within extracellular cadherin domains of a transmembrane receptor Fat and its ligand, Dachsous (Ds). Mutation of three conserved Asp residues at the Drosophila Fj putative active site abolished its ability to phosphorylate Ft and Ds cadherin domains. The Fat signaling pathway regulates growth, gene expression, and planar cell polarity (PCP). Defects from mutation in Drosophila Fj include loss of the intermediate leg joint, and a PCP defect in the eye. The expression of the Drospophila fj gene is modulated by Notch, Unpaired (JAK/STAT), and Wingless signals. Mouse Fjx1, has been shown to be involved in both the Fat and Hippo signaling pathways; these two pathways intersect at multiple points. The Hippo pathway is important in organ size control and in cancer. The expression of the mouse fjx1 gene is also Notch dependent; fjx1 is expressed in the brain, the peripheral nervous system, in epithelial structures of different organs, and during limb development.
Jiyao W et al.(2023). "The conserved domain database in 2023.",