We recently identified the leucine-rich repeat (LRR) adhesion protein, trophoblast glycoprotein (TPBG), as a novel PKCα-dependent phosphoprotein in retinal rod bipolar cells (RBCs). Since TPBG has not been thoroughly examined in the retina, this study characterizes the localization and expression patterns of TPBG in the developing and adult mouse retina using two antibodies, one against the N-terminal LRR domain and the other against the C-terminal PDZ-interacting motif. Both antibodies labeled RBC dendrites in the outer plexiform layer and axon terminals in the IPL, as well as a putative amacrine cell with their cell bodies in the inner nuclear layer (INL) and a dense layer in the middle of the inner plexiform layer (IPL). In live transfected HEK293 cells, TPBG was localized to the plasma membrane with the N-terminal LRR domain facing the extracellular space. TPBG immunofluorescence in RBCs was strongly altered by the loss of TRPM1 in the adult retina, with significantly less dendritic and axon terminal labeling in TRPM1 knockout compared to wild type, despite no change in total TPBG detected by immunoblotting. During retinal development, TPBG expression increases dramatically just prior to eye opening with a time course closely correlated with that of TRPM1 expression. In the retina, LRR proteins have been implicated in the development and maintenance of functional bipolar cell synapses, and TPBG may play a similar role in RBCs.
Keywords: RRID 2721181; RRID AB_10846469; RRID AB_2069567; RRID AB_2242334; RRID AB_2272148; RRID AB_2338052; RRID AB_2338680; RRID AB_2340745; RRID AB_2650427; RRID AB_2716622; RRID AB_2801549; RRID AB_399431; RRID AB_477375; RRID CVCL_0045; amacrine cell; development; RRID AB_11144484; leucine-rich repeat protein; retina; rod bipolar cell; synapse; trophoblast glycoprotein.
© 2019 Wiley Periodicals, Inc.