The murine homolog of the fibroblast growth factor-5 (FGF-5) gene has been cloned, and the sequence of the gene's three exons has been determined. The murine gene and the previously isolated human FGF-5 gene are substantially homologous within the coding sequences and in upstream sequences, which contain an additional open reading frame. We have used a portion of the murine gene as probe to detect FGF-5 RNA in adult mouse tissues by both Northern blot and in situ hybridization methods. FGF-5 RNA is present at low levels in widely distributed areas of the central nervous system. Several loci of FGF-5 expression could be localized by in situ hybridization and include portions of the cerebral cortex, hippocampus, and thalamus. Neuronal expression accounts for at least some of the FGF-5 RNA synthesized in the central nervous system. Fibroblast growth factors (FGFs) constitute a family of mitogenic proteins with related primary structures. Each mammalian factor, of which seven are now known, is encoded by a distinct gene (1)(2)(3)(4)(5)(6)(7)(8). FGFs are mitogenic towards a broad spectrum of mesodermal and ectodermal cells (9) and can act also as inducers (10-13) and inhibitors (14) of developmental pathways. Fibroblasts and endothelial cells can respond to several different FGFs (9). By contrast, keratinocyte growth factor, the most recently characterized FGF, does not stimulate fibroblast growth (15). Hence, FGFs may have overlapping but distinct spectra of activities.FGF-5 is a growth factor discovered in our laboratory as the product of a human oncogene detected by DNA transfection assays (6, 16). The protein is mitogenic towards fibroblasts and endothelial cells in vitro (6), but the natural targets for FGF-5 action in vivo have yet to be ascertained. As a first step towards an understanding of Genomic Library Screening. Murine NIH 3T3 DNA partially digested with Sau3aI was cloned into EMBL4 A phage DNA to generate one library, while another consisting of mouse spleen DNA cloned into A phage EMBL3 was obtained from F. Costantini. Libraries were screened by a standard procedure (17) using as probe human FGF-5 cDNA (6) labeled with 32P by random hexamer priming (18 RNA Filter Blot Hybridization. Tissues were dissected from 8-week-old C57BL/6 mice, and the RNA was isolated after solubilization in guanidinium isothiocyanate (21). RNA was also isolated from seven components of brain dissected by standard procedure (22). RNA filter blot hybridization after agarose gel electrophoresis followed a standard protocol (23) using a 32P-labeled Pst I/Sac I 450-bp DNA fragment containing exon 3 of the murine FGF-5 gene (see Fig. 1 *The sequences reported in this paper have been deposited in the GenBank data base (accession nos. M37821-4 for the murine FGF-5 gene and M37825 for the corrected human FGF-5 cDNA). 8022The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this f...

The mechanism of action of prolactin (PRL) was studied in murine lymphoid BAF‐3 cells transfected with either the long form of the PRL receptor (PRL‐R), or a chimeric receptor consisting of the extracellular domain of the PRL‐R and the transmembrane and intracellular domain of the erythropoietin receptor (PRL/EPO‐R). PRL sustained normal and long‐term proliferation of BAF‐3 cells expressing either the PRL‐R or the hybrid PRL/EPO‐R. Upon [125I]PRL cross‐linking, both types of BAF‐3 transfectants were shown to express two [125I]PRL cross‐linked species differing in size by 20 kDa. These cross‐linked complexes, after denaturation, were recognized by antibody against the PRL‐R, indicating that they contain the transfected receptor. PRL induced rapid and transient tyrosine phosphorylation of both the PRL‐R and the PRL/EPO‐R in BAF‐3 transfectants. Furthermore, PRL induced rapid tyrosine phosphorylation of the Janus kinase 2 (JAK2) which was already physically associated with the PRL‐R or the PRL/EPO‐R in the absence of ligand. JAK1 was also associated with PRL‐R and PRL/EPO‐R in the absence of ligand. However, only in BAF‐3 cells expressing the PRL‐R does PRL induce rapid and transient tyrosine phosphorylation of JAK1. These results demonstrate that JAK protein tyrosine kinases couple PRL binding to tyrosine phosphorylation and proliferation.

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