Serum factors and v-src control two complementary mitogenic pathways in quail neuroretinal cells in culture

Quail neuroretinal cells (QNR cells) from 7-day-old embryos do not proliferate even in the presence of 8% fetal calf serum. After infection by the Rous sarcoma virus (RSV) they proliferate actively and exhibit a transformed phenotype; this effect is mediated by the oncoprotein pp60v-src. Secondary cultures infected by the thermosensitive strain tsNY68 of RSV are blocked in G0 either by thermal inactivation of pp60v-src at 41.5 degrees C or by serum deprivation at the permissive temperature (36.5 degrees C). Cell division is reinduced either by pp60v-src thermal renaturation or by subsequent serum addition. Our results indicate that v-src and serum control two synergic pathways leading to G0/G1 transition in QNR cells. In order to characterize genes related to the mitogenic and transforming effects of v-src in nerve cells, we have constructed a cDNA library from QNR cells transformed by tsNY68. We report the properties of five molecular clones isolated by differential screening of this library. Unlike immediate-early genes like c-fos, they are induced in mid and late G1. Four of them correspond to unknown mRNAs and the last one codes for nucleolin. This set of v-src-regulated genes is likely to code for functions deficient in terminally differentiated QNR cells and necessary for the progression in G1.