A bag cell neuron-specific antigen localizes to a subset of dense core vesicles in Aplysia californica.

The bag cell neurons of Aplysia govern egg-laying through the release of a number of bioactive peptides which are processed from a common precursor. Immunoelectron microscopic studies suggest that sorting at the trans-Golgi segregates peptides from the amino terminal and carboxy terminal of the precursor into distinct classes of dense-cored vesicles (DCVs). Here we identify a novel bag cell-specific antigen (4F6 antigen) using monoclonal antibodies (MAbs). Immunoprecipitations and Western blots demonstrate that the MAb4F6 specifically recognizes a protein of 80 kDa and does not react with the egg-laying hormone precursor, processing intermediates or final products. The 4F6 antigen is localized in a subset of DCVs which also contain peptides derived from the amino terminus of the precursor. These results further demonstrate the complexity of vesicular sorting in the bag cells and also identify a novel tissue specific antigen localized to DCVs.