Small GTP-binding protein RhoB is expressed in glial Müller cells in the vertebrate retina.

Among several small Rho GTPases observed in the chick retina, RhoB was transiently expressed during development and mainly present in glial Müller cells in the adult. The aim of this study was to compare the distribution of RhoB in the chick and mouse adult retinas and to study its potential role in the maintenance of cell morphology. The distribution of RhoB was studied in situ and pure Müller cell cultures were submitted to Clostridium difficile toxin A and lysophosphatidic acid (LPA) treatment in order to inactivate and activate Rho proteins, respectively. Cell morphology, F-actin arrangement, RhoB, and vimentin distribution were studied by immunofluorescence and confocal microscopy. The results showed that, in both species, all vimentin-containing cells also expressed RhoB in situ and in vitro. Toxin A promoted cell rounding and detachment due to actin depolymerization, changing the distribution of RhoB only in chick cells. In serum-starved cells LPA stimulated actin polymerization and cell spreading, but only in chick cells was RhoB distribution recruited to expanding cellular processes and newly formed focal adhesions. These data suggest that, although RhoB is expressed by Müller cells in chick and mouse, its role in the maintenance of cellular morphology and regulation may be different. In addition, we show that RhoB may be an interesting Müller cell marker in the adult retina.