PROLIFERATION OF CHICKEN NEURORETINA CELLS INDUCED BY V-SRC, IN-VITRO, DEPENDS ON ACTIVATION OF THE E2F TRANSCRIPTION FACTOR

Quiescent chicken or quail retina neuroblasts (NR) can be induced to p roliferate actively, in culture, by the v-src oncoprotein. The chE2F-1 transcription factor, a physiological partner of the retinoblastoma g ene product, is highly expressed in vivo, in dividing chicken neuroret ina cells (CNR), It is sharply down-regulated as cells enter the post- mitotic differentiation stage, thus suggesting that E2F activity is a prerequisite for NR cell proliferation. In the present paper, transien t expression assays of different forms of chE2F-1 mere used to investi gate the function of E2F for switching CNR cells from a quiescent to a proliferative state in vitro. Attempts to substitute the effects of v -src by an ectopic expression of E2F-1 were unsuccessful. However, in the same conditions, E2F-1 supports full growth of CEF in serum-deplet ed medium, Deletion mutants of E2F-1, with potential dominant-negative properties, mere transfected in RSV infected CNR cells. One of these truncated mutants induces a G1 phase block in RSV-transformed CNR cell s indicating that, although E2F-1 overexpression cannot overcome the c ell proliferation block of postmitotic CNR cells E2F-1, activity is an important component of the growth signal pathway delivered by v-src i n these nervous cells.