During the development of the vertebrate nervous system, many neurons depend for survival on interactions with their target cells. Specific proteins are thought to be released by the target cells and to play an essential role in these interactions. So far, only one such protein, nerve growth factor, has been fully characterized. This has been possible because of the extraordinarily (and unexplained) large quantities of this protein in some adult tissues that are of no relevance to the developing nervous system. Whereas the dependency of many neurons on their target cells for normal development, and the restricted neuronal specificity of nerve growth factor have long suggested the existence of other such proteins, their low abundance has rendered their characterization difficult. Here we report the full primary structure of brain-derived neurotrophic factor. This very rare protein is known to promote the survival of neuronal populations that are all located either in the central nervous system or directly connected with it. The messenger RNA for brain-derived neurotrophic factor was found predominantly in the central nervous system, and the sequence of the protein indicates that it is structurally related to nerve growth factor. These results establish that these two neurotrophic factors are related both functionally and structurally.

We report the identification of ligands for Tyro 3 (alternatively called Sky, rse, brt, or tif) and Axl (alternatively, Ark or UFO), members of a previously orphan family of receptor-like tyrosine kinases. These ligands correspond to protein S, a protease regulator that is a potent anticoagulant, and Gas6, a protein related to protein S but lacking any known function. Our results are reminiscent of recent findings that the procoagulant thrombin, a protease that drives clot formation by cleaving fibrinogen to form fibrin, also binds and activates intracellular signaling via a G protein-coupled cell surface receptor. Proteases and protease regulators that also activate specific cell surface receptors may serve to integrate coagulation with associated cellular responses required for tissue repair and growth, as well as to coordinate protease cascades and associated cellular responses in other systems, such as those involved in growth and remodeling of the nervous system.

cDNA clones corresponding to a mRNA whose level is rapidly increased by addition of oestradiol to the culture medium have been isolated by differential screening of a cDNA library from the breast cancer cell line MCF-7, which contains oestrogen receptors. Such clones will be useful in studies of the DNA sequences required for hormonal induction and to determine whether expression of the corresponding gene is in any way related to the cancerous state. We have also obtained a cDNA clone for a messenger whose level is apparently decreased by steroid hormones.

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Receptor tyrosine kinases often have critical roles in particular cell lineages by initiating signalling cascades in those lineages. Examples include the neural-specific TRK receptors, the VEGF and angiopoietin endothelial-specific receptors, and the muscle-specific MUSK receptor. Many lineage-restricted receptor tyrosine kinases were initially identified as 'orphans' homologous to known receptors, and only subsequently used to identify their unknown growth factors. Some receptor-tyrosine-kinase-like orphans still lack identified ligands as well as biological roles. Here we characterize one such orphan, encoded by Ror2 (ref. 12). We report that disruption of mouse Ror2 leads to profound skeletal abnormalities, with essentially all endochondrally derived bones foreshortened or misshapen, albeit to differing degrees. Further, we find that Ror2 is selectively expressed in the chondrocytes of all developing cartilage anlagen, where it essential during initial growth and patterning, as well as subsequently in the proliferating chondrocytes of mature growth plates, where it is required for normal expansion. Thus, Ror2 encodes a receptor-like tyrosine kinase that is selectively expressed in, and particularly important for, the chondrocyte lineage.

We present the complete sequence of an mRNA which is induced by estrogen in the human breast cancer cell line MCF-7 [pS2 mRNA, Masiakowski et al., Nucleic Acids Res. 10, 7895-7903 (1982)]. Primer extension and cloning of double-stranded cDNA (ds-cDNA) into a vector designed to make full-length cDNA were used to determine the sequence of the fifteen 5'-terminal nucleotides which were not present in the original pS2 ds-cDNA clone. The mRNA sequence has a major open reading frame encoding 84 amino-acids, flanked by a 40 nucleotide 5'-untranslated region and a 198 nucleotide 3'-untranslated region preceding the polyA tail. The 3'-untranslated region contains a polyadenylation signal, AUUAAA, 14 nucleotides upstream from the polyA tail. The derived protein sequence contains a putative signal peptide region suggesting that the protein may be secreted. The nucleotide and derived amino-acid sequences were compared to previously determined sequences, particularly to those of hormone-regulated proteins and growth factors, and no obvious similarities were observed.

Differential hybridization of a cDNA library from rat pheochromocytoma PC12 cells with cDNA probes from naive PC12 cells and from PC12 cells exposed to nerve growth factor for 7 days identified cDNA sequences of two genes induced by NGF. The mRNA species detected by these cDNA sequences, designated 42A and 42C, reached maximal levels after 24 hr of treatment with NGF and were still significantly higher than control levels after 7 days. Epidermal growth factor transiently induced both mRNAs but at much lower levels. The mRNAs code for 95-(42C) and 101-(42A) amino acid residue peptides whose sequences are homologous to those of a family of calcium-binding proteins including the S-100 protein. The conservation of primary and secondary structure between 42A, 42C, and the other proteins suggests a possible role for them in the regulation of cell growth and differentiation.