I'm studying a neuroscientific paper, and in it the authors state that "defensive behaviors are mediated by a BLA population of magnocellular R-spondin 2-expressing (RSPO2⁺) neurons".
I know that R-spondin 2 is a protein, but what is the meaning of R-spondin 2-expressing neurons? What is an x-expressing neuron, with x = some protein?
Thank you very much.