Immunocytochemical characterisation of rabbit and mouse embryonic fibroblasts

By using indirect immunofluorescence we demonstrated the localisation of extracellular matrix (ECM) proteins (laminin--LAM, collagen IV--COL IV, fibronectin--FN) and the basic fibroblast growth factor (bFGF) in rabbit and mouse primary embryonic fibroblasts (PEF). Proliferating mitotically arrested PEF (by mitomycin C) were compared in both species. The stability of protein expression was ascertained during the first five successive passages. In addition, STO cells (i.e. permanent line of irradiated mouse fibroblasts) were similarly analysed. Rabbit PEF showed very high extracellular staining for FN and a negligible cytoplasmic positivity for LAM and COL IV. A totally reversed staining pattern for ECM proteins was found in mouse PEF. A dense cytoplasmic granulation (concentrated around the nucleus) was revealed for LAM and COL IV and almost no reaction for FN. The staining patterns were very stable at the culture conditions we applied. They were maintained during the first five successive passages in proliferating as well as non-proliferating mouse and rabbit PEF and were independent of cell concentration (individually dispersed cells versus cells in a confluent layer). STO cells showed the same staining for ECM proteins as the mouse PEF, thus confirming their origin from the same animal species. Light granular staining for bFGF was found in the cytoplasm of proliferating and mitotically arrested rabbit and mouse PEF and STO cells. The differences in expression of ECM proteins between the rabbit and mouse PEF, as well as the synthesis of bFGF, should be taken into consideration when these cells are used in vitro as a feeder layer for various cells (e.g. embryonic stem cells).