Transforming growth factor beta (TGFβ) is a potent trophic factor for midbrain dopamine (DA) neurons, but its in vivo function and signaling mechanisms are not entirely understood. We show that the transcriptional cofactor homeodomain interacting protein kinase 2 (HIPK2) is required for the TGFβ-mediated survival of mouse DA neurons. The targeted deletion of Hipk2 has no deleterious effect on the neurogenesis of DA neurons, but leads to a selective loss of these neurons that is due to increased apoptosis during programmed cell death. As a consequence, Hipk2 −/− mutants show an array of psychomotor abnormalities. The function of HIPK2 depends on its interaction with receptor-regulated Smads to activate TGFβ target genes. In support of this notion, DA neurons from Hipk2 −/− mutants fail to survive in the presence of TGFβ3 and Tgfβ3 −/− mutants show DA neuron abnormalities similar to those seen in Hipk2 −/− mutants. These data underscore the importance of the TGFβ-Smad-HIPK2 pathway in the survival of DA neurons and its potential as a therapeutic target for promoting DA neuron survival during neurodegeneration.Ventral midbrain DA neurons in the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA) control extrapyramidal movement and a variety of cognitive

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To characterize the potential role of cAMP in pheromone transduction, we have examined the occurrence of cyclic nucleotide phosphodiesterases (PDEs) in the mouse vomeronasal organ (VNO). We show that the cAMP-specific isoforms PDE4A and PDE4D are found preferentially in the apical and basal layers, respectively, of the VNO neuroepithelium and in the rostral (PDE4A) and caudal (PDE4D) portions of the accessory olfactory bulb glomerular layer. Assays for cAMP hydrolysis showed that PDE activity in VNO homogenates was about half that measured in the cerebral cortex and olfactory epithelium, and the proportion of total activity inhibited by rolipram, a PDE4-specific inhibitor, was approximately 40%. Activity in the VNO was enhanced 60% by Ca(2+) and calmodulin (CaM), implicating the presence of Ca(2+)/CaM-dependent PDE1. Zaprinast, which is known to inhibit PDE1C isoforms, completely suppressed Ca(2+)/CaM-stimulated activity and, together, zaprinast and rolipram inhibited cAMP hydrolysis by approximately 70%. Our results suggest that PDE1 and PDE4 isoforms are the primary source of cAMP degradation in the VNO.

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