Analysis of prolactin-modulated gene expression profiles during the Nb2 cell cycle using differential screening techniques

About 70 transcripts were found to be modulated in Nb2 cells following prolactin treatment. Of these, approximately 20 represent unknown genes. All cDNAs were characterized by northern blot analysis and categorized on the basis of their expression profiles and the functions of the known genes. We compared our data with other cell-cycle-regulated transcripts and found several new potential signaling molecules that may be involved in Nb2 cell growth. In addition, abnormalities in the expression patterns of several transcripts were detected in Nb2 cells, including the constitutive expression of the immediate-early gene EGR-1. Finally, we compared the differential screening techniques in terms of sensitivity, efficiency and occurrence of false positives.Using these techniques to determine which genes are differentially expressed in Nb2 lymphoma cells, we have obtained valuable insight into the potential functions of some of these genes in the cell cycle. Although this information is preliminary, comparison with other eukaryotic models of cell-cycle progression enables identification of expression abnormalities and proteins potentially involved in signal transduction, which could indicate new directions for research.Prolactin is a pleiotropic hormone whose numerous actions are associated with reproduction, growth and development, water and electrolyte balance, metabolism, behavior and immunoregulation [1]. The prolactin-dependent rat Nb2 lymphoma (Nb2-11C) is widely used as a model in which to study signal transduction and transcriptional mechanisms that underlie prolactin-stimulated mitogenesis (reviewed in [1,2,3]). Deprivation of lactogen induces a block in the early G1 phase of the Nb2 cell cycle [4]. The addition of physiological concentrations of prolactin to synchronized G0/G1-arrested cultures reinitiates cell-cycle progression [5], which is characterized by the induction of growth-related genes such as those for c-Myc, ？-actin and ornithine decarboxylase (ODC) a