Medulloblastoma, the most common malignant brain tumor of childhood, has a variable prognosis. Although half of the children and young adults with the disease survive longer than 10 years after diagnosis, the others relapse and die despite identical therapy. We have examined the expression of neurotrophins and their receptors in medulloblastoma samples snap frozen in the operating room to preserve RNA integrity. All tumors (n = 12) were found to express mRNA encoding neurotrophin 3 and its receptor TrkC. The level of trkC expression was highly variable, with a more than 50-fold difference between the highest and lowest values. By Kaplan-Meier analysis, patients with tumors expressing high levels of trkC mRNA had significantly longer intervals without disease progression than those with low levels (log-rank, P = 0.03) and a more favorable overall survival (log-rank, P = 0.05). Thus, trkC expression is a prognostic indicator for patients with medulloblastoma.

The synthesis of the protamines, the predominant nuclear proteins of mammalian spermatozoa, is regulated during germ cell development by mRNA storage for about 7 days in the cytoplasm of differentiating spermatids. Two Many eukaryotic mRNAs contain regulatory elements that control their posttranscriptional utilization. These regulatory elements often reside within the 5' and 3' untranslated regions (UTRs) of mRNAs and interact with specific cytoplasmic proteins that modulate stability or translational competence of mRNAs. One of the best-characterized systems for such posttranscriptional control involves cellular iron transport and utilization. An iron-responsive-element binding protein interacts with the iron-responsive elements present in the UTRs of ferritin, erythroid 5-aminolevulinate synthase, and transferrin receptor mRNAs to mediate their coordinate translational regulation in response to changing levels of cellular iron (for reviews, see references 26 and 42).Translational regulation also plays a crucial role in programming early development, since many mRNAs are stored in translationally inactive states until their utilization at specific stages of development (for reviews, see references 49 and 51). In Xenopus and Spisula oocytes, mRNAs are stored as masked mRNAs, messenger ribonucleoprotein particles (mRNPs), in which the protein components are believed to act as repressors of translation (47,48). In Spisula oocytes, the ribonucleotide reductase and cyclin A mRNAs have been demonstrated to possess protein-binding regions in their 3' UTRs which regulate their translation (52).During spermatogenesis, spermatogonia, diploid male germ cells, divide to maintain a pool of cells, some of which differentiate and undergo meiosis. After the meiotic divisions, the germ cells enter spermiogenesis, the haploid phase of spermatogenesis, where round spermatids differentiate into elongating spermatids and ultimately spermatozoa. During spermiogenesis, the germ cell nuclei undergo a major reorganization in which the somatic and testicular histones are replaced by transition proteins (TPs), which are in turn * Corresponding author. t Present address:

We used anti-phosphopeptide-immunodetecting antibodies as immunohistochemical reagents to define the location and activity state of p185 erbB2 during Wallerian degeneration. Nerve damage induces a phosphorylation event at Y1248, a site that couples p185 erbB2 to the Ras-Raf-MAP kinase signal transduction pathway. Phosphorylation of p185 erbB2 occurs within Schwann cells and coincides in time and space with Schwann cell mitotic activity, as measured by bromodeoxyuridine uptake. These visual images of receptor autophosphorylation link activation of p185 erbB2 to the Schwann cell proliferation that accompanies nerve regeneration. Key words: neuregulin; erbB2; receptor tyrosine kinase; Schwann cell; Wallerian degeneration; phosphotyrosineUnlike elements of the C NS, peripheral nerves can regenerate when damaged. Understanding the regulation of this process has practical implications for treatment of peripheral neuropathies such as those secondary to diabetes, cancer chemotherapeutic agents, and other toxins. Moreover, insights into peripheral nerve regeneration may be transferable to treatment of spinal cord injuries. After peripheral nerves are damaged, they initially undergo Wallerian degeneration. Axons distal to the site of injury degenerate, and their myelin sheaths break down. Schwann cells then proliferate, providing a context for axonal regrowth and nerve regeneration (Waller, 1851;Fawcett and Keynes, 1990). Although Schwann cell proliferation is a prominent feature of nerve regeneration, the molecular signals driving the mitotic response have not been characterized.One viable candidate for regulating the Schwann cell proliferation that accompanies regeneration of peripheral nerves is the transmembrane tyrosine protein kinase p185 erbB2 . Schwann cells express p185 erbB2 both in culture and in vivo (Jin et al., 1993;Marchionni et al., 1993). The tyrosine kinase activity of p185 erbB2 is activated by a family of ligands known collectively as the neuregulins (glial growth factor, acetylcholine receptor-inducing activity, Neu differentiation factor, and heregulin) that are encoded as splice variant transcripts of a common gene. Neuregulins are expressed by neurons in the peripheral nervous system (Marchionni et al., 1993;Dong et al., 1995), and they promote the proliferation of Schwann cells in vitro (Marchionni et al., 1993;Marchionni, 1995;Morrissey et al., 1995).Activation of the p185 erbB2 tyrosine kinase results in the autophosphorylation of specific tyrosines on the intracellular domain of the receptor. This autophosphorylation can be monitored with anti-phosphotyrosine antibodies. However, reactivity with generic antibodies to phosphotyrosine provides no specific insight into the catalytic or signaling activities of a growth factor receptor. Moreover, anti-phosphotyrosine antibodies cannot be used as receptor-specific histochemical reagents. To determine the cellular location and activity state of p185 erbB2 during Wallerian degeneration, we exploited the fact that synthetic tyrosine phosphopeptides, cor...