Adult dentate neurogenesis is important for certain types of hippocampal-dependent learning and also appears to be important for the maintenance of normal mood and the behavioural effects of antidepressants. Neuropeptide Y (NPY), a peptide neurotransmitter released by interneurons in the dentate gyrus, has important effects on mood, anxiety-related behaviour and learning and memory. We report that adult NPY Y -/-1 receptor knock-out mice have significantly reduced cell proliferation and significantly fewer immature doublecortinpositive neurons in the dentate gyrus. We also show that the neuroproliferative effect of NPY is dentate specific, is Y 1 -receptor mediated and involves extracellular signal-regulated kinase (ERK)1/2 activation. NPY did not exhibit any effect on cell survival in vitro but constitutive loss of the Y 1 receptor in vivo resulted in greater survival of newly generated neurons and an unchanged total number of dentate granule cells. These results show that NPY stimulates neuronal precursor proliferation in the dentate gyrus and suggest that NPYreleasing interneurons may modulate dentate neurogenesis.

The neuropeptide Y (NPY) system has been implicated in the regulation of bone homeostasis and osteoblast activity, but the mechanism behind this is unclear. Here we show that Y1 receptor signaling is directly involved in the differentiation of mesenchymal progenitor cells isolated from bone tissue, as well as the activity of mature osteoblasts. Importantly, the mRNA levels of two key osteogenic transcription factors, runx2 and osterix, as well as the adipogenic transcription factor PPAR-g, were increased in long bones of Y1 À/À mice compared with wild-type mice. In vitro, bone marrow stromal cells (BMSCs) isolated from Y1 À/À mice formed a greater number of mineralized nodules under osteogenic conditions and a greater number of adipocytes under adipogenic conditions than controls. In addition, both the number and size of fibroblast colony-forming units formed in vitro by purified osteoprogenitor cells were increased in the absence of the Y1 receptors, suggestive of enhanced proliferation and osteogenesis. Furthermore, the ability of two specific populations of mesenchymal progenitor cells isolated from bone tissue, an immature mesenchymal stem cell population and a more committed osteoprogenitor cell population, to differentiate into osteoblasts and adipocytes in vitro was enhanced in the absence of Y1 receptor signaling. Finally, Y1 receptor deletion also enhanced the mineral-producing ability of mature osteoblasts, as shown by increased in vitro mineralization by BMSCs isolated from osteoblast-specific Y1 À/À mice. Together these data demonstrate that the NPY system, via the Y1 receptor, directly inhibits the differentiation of mesenchymal progenitor cells as well as the activity of mature osteoblasts, constituting a likely mechanism for the high-bone-mass phenotype evident in Y1 À/À mice. ß

Neuropeptide Y, Y1 receptors are found in neuronal as well as bone tissue and Y1 signalling has been implicated in the regulation of bone mass. However, the contribution of Y1 receptors located in these different tissues, particularly that of the bone-specific Y1 receptors, to the regulation of bone homeostasis is unclear. Here we demonstrate that osteoblastspecific Y1 receptor deletion resulted in a marked increase in femoral cancellous bone volume, trabecular thickness and trabecular number. This is the result of elevated osteoblast activity as shown by increased mineral apposition rate and bone formation rate, and is associated with an upregulation in the mRNA expression levels of alkaline phosphatase, osteocalcin and dentin matrix protein-1. Furthermore, osteoblastic Y1 receptor deletion also led to increased mineral apposition rate on both the endocortical and the periosteal surfaces resulting in increased femoral diameter. Together these data demonstrate a direct role for the Y1 receptor on osteoblasts in the regulation of osteoblast activity and bone formation in vivo and suggest that targeting Y1 receptor signalling directly in the bone may have potential therapeutic implications for stimulating bone accrual in diseases such as osteoporosis.

While the regenerative capacity of the olfactory neuroepithelium has been well studied less is known about the molecular events controlling precursor cell activity. Neuropeptide Y (NPY) is expressed at high levels in the olfactory system, and NPY has been shown to play a role in neuroregeneration of the brain. In this study, we show that the numbers of olfactory neurospheres derived from NPY, NPY/peptide YY, and Y1 receptor knockout mice are decreased compared with wild type (WT) controls. Furthermore, flow cytometric analysis of isolated horizontal basal cells, globose basal cells, and glandular cells showed that only glandular cells derived from WT mice, but not from NPY and Y1 receptor knockout mice, formed secondary neurospheres suggesting a critical role for NPY signaling in this process. Interestingly, olfactory function tests revealed that olfaction in Y1 knockout mice is impaired compared with those of WT mice, probably because of the reduced number of olfactory neurons formed. Together these results indicate that NPY and the Y1 receptor are required for the normal proliferation of adult olfactory precursors and olfactory function.

Many forms of deafness result from degeneration of the sensory cells for hearing, the hair cells in the cochlea. Stem cells offer a potential cell-based therapy for the treatment of deafness. Here, we investigate whether adult olfactory precursor cells can differentiate into hair cells in culture. Precursor cells were isolated from mouse olfactory neuroepithelium, were sphere-forming, showed proliferative capacity, and contained cells expressing neuronal and nonneuronal proteins. To induce differentiation, precursor cells were cocultured with cochlear cells and/or cochlear supernatant. Differentiated precursor cells were immunopositive for specific hair cell markers, including myosin VIIa, FM1-43, calretinin, phalloidin, and espin, and resembled hair cells anatomically and immunocytochemically in culture. The results demonstrate for the first time that adult olfactory precursor cells can differentiate into hair cell-like cells, thus providing a potential autotransplantation therapy for hearing loss. STEM CELLS 2007;25:621-627

The molecular isoform of the cDNA clone Isk present in the AT-1 atrial tumor cell line was characterized by molecular cloning of Isk cDNA. Since Isk mRNA was found in mouse heart, kidney, and uterus, a complete study of its expression during development in the heart and kidney was performed, in addition to its expression in the uterus during pregnancy. In the heart, Isk showed a 4-fold upregulation during the perinatal period followed by a 20-fold decrease between birth and the adult state. Furthermore, the two 0.9- and 3.4-kb transcripts were differentially regulated after birth. In the kidney, Isk progressively increased 10-fold, reaching steady-state adult values at 21 days. Isk mRNA levels in the uterus increased threefold at late pregnancy and decreased sixfold rapidly after birth. The Isk gene is differentially expressed during development in kidney and cardiac tissue, and both Isk transcripts appeared to be differentially regulated. Furthermore, the drastic changes in transcript levels before delivery and after birth suggest that Isk plays a significant role in myometrium during late pregnancy and delivery.

The intermediate filament protein nestin has been widely used as a marker for proliferating neural progenitor cells in the nervous system. The mammalian olfactory neuroepithelium is a region of the nervous system that robustly supports ongoing neurogenesis, yet where nestin has not been reported to mark proliferating progenitors. Using immunohistochemistry, we examined nestin expression in the mature olfactory neuroepithelium and found it to be tightly restricted to the basal compartment where the olfactory neuronal progenitor cell population resides. The pattern of nestin immunoreactivity was consistent with expression by the endfeet and inferior processes of sustentacular cells rather than basal cells. Using a bank of defined antibody markers, we confirmed nestin's pattern of distribution to be different from that of cytokeratin, vimentin, GBC-1, GAP43, and carnosine. It was highly similar to the pattern of SUS-4 immunoreactivity in the basal region of the neuroepithelium. Following surgical bulbectomy, nestin expression was up-regulated and became evident in the cell bodies of sustentacular cells situated more apically in the neuroepithelium. We have shown nestin to be present in the basal region of the adult olfactory neuroepithelium in the zone that supports ongoing neurogenesis in the adult, but its expression is restricted to the inferior parts of sustentacular cells rather than the neuronal progenitor cells. Nestin may play a potential role in the migration of recently proliferated olfactory neurons on the scaffolding of sustentacular cells in a manner analogous to its proposed role in radial glia during embryonic development of the central nervous system.

mNav2.3 is a putative voltage-dependent sodium channel (NaC) gene expressed in both mouse heart and uterus that shares only 45% amino acid identity with NaCs from gene subfamily 1. Immunofluorescence studies using polyclonal antibodies against two distinct epitopes revealed that mNav2.3 protein in heart colocalized with nerve-specific antibody binding. Similar mNav2.3-specific antibody staining was observed in virgin uterus. However, mNav2.3 expression in uterine nerve disappeared during late pregnancy, concurrent with an appearance in both the longitudinal and circular uterine smooth muscle, which reached a maximum at term and quickly declined within 2 days postpartum. mNav2.3 expression in term uterus often colocalized on the myocyte surface with connexin 43. The immunofluorescence results are supported by Western analysis in which the 217-kDa NaC increased during late pregnancy and declined 2 days postpartum. These data provide perhaps the most dramatic example of NaC regulation. The acute and transient upregulation in myometrium during gestation suggests the Nav2.3 channel plays a role in uterine function at term.