Erythropoietin (EPO) is both hematopoietic and tissue protective, putatively through interaction with different receptors. We generated receptor subtype–selective ligands allowing the separation of EPO's bioactivities at the cellular level and in animals. Carbamylated EPO (CEPO) or certain EPO mutants did not bind to the classical EPO receptor (EPOR) and did not show any hematopoietic activity in human cell signaling assays or upon chronic dosing in different animal species. Nevertheless, CEPO and various nonhematopoietic mutants were cytoprotective in vitro and conferred neuroprotection against stroke, spinal cord compression, diabetic neuropathy, and experimental autoimmune encephalomyelitis at a potency and efficacy comparable to EPO.

Insulin-like growth factor II (IGF-II) is a major fetal growth factor. The IGF-II gene generates multiple mRNAs with different 5′ untranslated regions (5′ UTRs) that are translated in a differential manner during development. We have identified a human family of three IGF-II mRNA-binding proteins (IMPs) that exhibit multiple attachments to the 5′ UTR from the translationally regulated IGF-II leader 3 mRNA but are unable to bind to the 5′ UTR from the constitutively translated IGF-II leader 4 mRNA. IMPs contain the unique combination of two RNA recognition motifs and four hnRNP K homology domains and are homologous to the Xenopus Vera and chicken zipcode-binding proteins. IMP localizes to subcytoplasmic domains in a growth-dependent and cell-specific manner and causes a dose-dependent translational repression of IGF-II leader 3 –luciferase mRNA. Mouse IMPs are produced in a burst at embryonic day 12.5 followed by a decline towards birth, and, similar to IGF-II, IMPs are especially expressed in developing epithelia, muscle, and placenta in both mouse and human embryos. The results imply that cytoplasmic 5′ UTR-binding proteins control IGF-II biosynthesis during late mammalian development.

Insulin-like growth factor II mRNA-binding protein 1 (IMP1) belongs to a family of RNA-binding proteins implicated in mRNA localization, turnover, and translational control. Mouse IMP1 is expressed during early development, and an increase in expression occurs around embryonic day 12.5 (E12.5). To characterize the physiological role of IMP1, we generated IMP1-deficient mice carrying a gene trap insertion in the Imp1 gene. Imp1^−/− mice were on average 40% smaller than wild-type and heterozygous sex-matched littermates. Growth retardation was apparent from E17.5 and remained permanent into adult life. Moreover, Imp1^−/− mice exhibited high perinatal mortality, and only 50% were alive 3 days after birth. In contrast to most other organs, intestinal epithelial cells continue to express IMP1 postnatally, and Imp1^−/− mice exhibited impaired development of the intestine, with small and misshapen villi and twisted colon crypts. Analysis of target mRNAs and global expression profiling at E12.5 indicated that Igf2 translation was downregulated, whereas the postnatal intestine showed reduced expression of transcripts encoding extracellular matrix components, such as galectin- 1, lumican, tenascin-C, procollagen transcripts, and the Hsp47 procollagen chaperone. Taken together, the results demonstrate that IMP1 is essential for normal growth and development. Moreover, IMP1 may facilitate intestinal morphogenesis via regulation of extracellular matrix formation.

Active cytoplasmic RNA localization depends on the attachment of RNA-binding proteins that dictate the destination of the RNA molecule. In this study, we used an electrophoretic mobility-shift assay in combination with equilibrium and kinetic analyses to characterize the assembly of the human zipcode-binding protein IMP1 on targets in the 3′-UTR from Igf-II mRNA and in H19 RNA. In both cases, two molecules of IMP1 bound to RNA by a sequential, cooperative mechanism, characterized by an initial fast step, followed by a slow second step. The first step created an obligatory assembly intermediate of low stability, whereas the second step was the discriminatory event that converted a putative RNA target into a ‘locked’ stable RNP. The ability to dimerize was also observed between members of the IMP family of zipcode-binding proteins, providing a multitude of further interaction possibilities within RNP granules and with the localization apparatus.

Disturbances of the basal ganglia processes is heavily involved in schizophrenia. Phosphodiesterase 10A (PDE10A) is a basal ganglia specific hydrolase, which plays an essential role in regulating cAMP/PKA and cGMP/PKG signalling cascades by controlling the magnitude, duration and cellular location of cAMP/cGMP elevation. Biochemical and behavioral data indicate that PDE10A inhibition activates cAMP/PKA signalling in the basal ganglia, leading to the potentiation of dopamine D₁ receptor signalling, and concomitant inhibition of dopamine D₂ receptor signalling. Preclinical evidence in a range of animal models suggests that a PDE10A inhibitor could provide efficacy on positive, cognitive and negative symptoms of schizophrenia and PDE10A inhibitors are currently being evaluated in clinical trials for the treatment of schizophrenia.