Transient expression of neurotensin mRNA in the mitral cells of rat olfactory bulb during development

Targeting KDM1A in Neuroblastoma with NCL-1 Induces a Less Aggressive Phenotype and Suppresses Angiogenesis

Background: The KDM1A histone demethylase regulates the cellular balance between proliferation and differentiation, and is often deregulated in human cancers including the childhood tumor neuroblastoma. We previously showed that KDM1A is strongly expressed in undifferentiated neuroblastomas and correlates with poor patient prognosis, suggesting a possible clinical benefit from targeting KDM1A. Methods: Here, we tested the efficacy of NCL-1, a small molecule specifically inhibiting KDM1A in preclinical models for neuroblastoma. Results: NCL-1 mimicked the effects of siRNA-mediated KDM1A knockdown and effectively inhibited KDM1A activity in four neuroblastoma cell lines and a patient-representative cell model. KDM1A inhibition shifted the aggressive tumor cell phenotypes towards less aggressive phenotypes. The proliferation and cell viability was reduced, accompanied by the induction of markers of neuronal differentiation. Interventional NCL-1 treatment of nude mice harboring established neuroblastoma xenograft tumors reduced tumor growth and inhibited cell proliferation. Reduced vessel density and defects in blood vessel construction also resulted, and NCL-1 inhibited the growth and tube formation of HUVEC-C cells in vitro. Conclusions: Inhibiting KDM1A could attack aggressive neuroblastomas two-fold, by re-directing tumor cells toward a less aggressive, slower-growing phenotype and by preventing or reducing the vascular support of large tumors.

RNA-seq analysis of developing olfactory bulb projection neurons

Transmission of olfactory information to higher brain regions is mediated by olfactory bulb (OB) projection neurons, the mitral and tufted cells. Although mitral/tufted cells are often characterized as the OB counterpart of cortical projection neurons (also known as pyramidal neurons), they possess several unique morphological characteristics and project specifically to the olfactory cortices. Moreover, the molecular networks contributing to the generation of mitral/tufted cells during development are largely unknown. To understand the developmental patterns of gene expression in mitral/tufted cells in the OB, we performed transcriptome analyses targeting purified OB projection neurons at different developmental time points with next-generation RNA sequencing (RNA-seq). Through these analyses, we found 1202 protein-coding genes that are temporally differentially-regulated in developing projection neurons. Among them, 388 genes temporally changed their expression level only in projection neurons. The data provide useful resource to study the molecular mechanisms regulating development of mitral/tufted cells. We further compared the gene expression profiles of developing mitral/tufted cells with those of three cortical projection neuron subtypes, subcerebral projection neurons, corticothalamic projection neurons, and callosal projection neurons, and found that the molecular signature of developing olfactory projection neuron bears resemblance to that of subcerebral neurons. We also identified 3422 events that change the ratio of splicing isoforms in mitral/tufted cells during maturation. Interestingly, several genes expressed a novel isoform not previously reported. These results provide us with a broad perspective of the molecular networks underlying the development of OB projection neurons.

Developmental dynamics of neurotensin binding sites in the human hypothalamus during the first postnatal year

The aim of the present study was to determine a detailed mapping of neurotensin (NT) in the human hypothalamus, during the first postnatal year using an in vitro quantitative autoradiography technique and the selective radioligand monoiodo-Tyr3-NT. Ten human postmortem hypothalami obtained from control neonates and infants (aged from 2 h to 1 year of postnatal age) were used. The biochemical kinetics of the binding in all obtained in this study revealed that the binding affinity constants were of high affinity (in the nanomolar range) and did not differ significantly between all cases investigated. Furthermore, competition experiments show insensitivity to levocabastine and were in favor of the presence of the high affinity site of NT receptor. Autoradiographic distribution showed that NT binding sites were widely distributed throughout the rostrocaudal extent of the hypothalamus. However, the distribution of NT binding sites was not homogenous and regional variations exist. In general, the highest densities were mainly present in the anterior hypothalamic level, particularly in the preoptic area. High NT binding site densities are also present at the mediobasal hypothalamic level, particularly in the paraventricular, parafornical, and dorsomedial nuclei. At the posterior level, low to very low densities could be observed in all the mammillary complex subdivisions, as well as the posterior hypothalamic area. Although this topographical distribution is almost identical during the postnatal period analyzed, age-related variations exist in discrete structures of the hypothalamus. The densities were higher in neonates/less aged infants than older infants in preoptic area (medial and lateral parts). The developmental profile is characterized by a progressive decrease from the neonate period to 1 year of postnatal age with a tendency to reach adult levels. On the other hand, the low levels of NT binding sites observed in posterior hypothalamus did not vary during the first postnatal year. They contrast in that with the very high levels we reported previously in adult. In conclusion, the present study demonstrates the occurrence of high NT binding sites density in various structures in many regions in the human neonate/infant hypothalamus, involved in the control of neuroendocrine and/or neurovegetative functions.

Development and topography of the lateral olfactory tract in the mouse: imaging by genetically encoded and injected fluorescent markers

In mammals, conventional odorants are detected by OSNs located in the main olfactory epithelium of the nose. These neurons project their axons to glomeruli, which are specialized structures of neuropil in the olfactory bulb. Within glomeruli, axons synapse onto dendrites of projection neurons, the mitral and tufted (M/T) cells. Genetic approaches to visualize axons of OSNs expressing a given odorant receptor have proven very useful in elucidating the organization of these projections to the olfactory bulb. Much less is known about the development and connectivity of the lateral olfactory tract (LOT), which is formed by axons of M/T cells connecting the olfactory bulb to central neural regions. Here, we have extended our genetic approach to mark M/T cells of the main olfactory bulb and their axons in the mouse, by targeted insertion of IRES-tauGFP in the neurotensin locus. In NT-GFP mice, we find that M/T cells of the main olfactory bulb mature and project axons as early as embryonic day 11.5. Final innervation of central areas is accomplished before the end of the second postnatal week. M/T cell axons that originate from small defined areas within the main olfactory bulb, as visualized by localized injections of fluorescent tracers in wild-type mice at postnatal days 1 to 3, follow a dual trajectory: a branch of tightly packed axons along the dorsal aspect of the LOT, and a more diffuse branch along the ventral aspect. The dorsal, but not the ventral, subdivision of the LOT exhibits a topographical segregation of axons coming from the dorsal versus ventral main olfactory bulb. The NT-GFP mouse strain should prove useful in further studies of development and topography of the LOT, from E11.5 until 2 weeks after birth.

Locally born olfactory bulb stem cells proliferate in response to insulin-related factors and require endogenous insulin-like growth factor-I for differentiation into neurons and glia

After late embryogenesis, new neurons are continuously added to the olfactory bulb (OB) from stem cells located in the forebrain subventricular zone. Nonetheless, stem cells have not been described within the embryonic olfactory bulb. Here we report the isolation of local olfactory bulb stem cells from the embryonic day 12.5-14.5 mouse embryo. These cells were 99.2% nestin positive and proliferated extensively in culture to at least 150 cell doublings. Clonal analysis demonstrated that neurons (TuJ1(+)), astrocytes (GFAP(+)), and oligodendrocytes (O4(+)) could be generated from single-plated cells, indicating that they are multipotent. At least 90% of proliferating cells expressed insulin-like growth factor-I (IGF-I), (pro)insulin, and their cognate receptors; these growth factors collaborated with fibroblast growth factor-2 plus epidermal growth factor (EGF) to promote stem cell proliferation and sphere formation. Cells from Igf-I(-)/- mice, however, proliferated as extensively as did Igf-I(+/+) cells. Differentiation and survival of stem cell-generated neurons and glia showed strong dependence on exogenous IGF-I, but oligodendrocyte differentiation also required insulin at low concentration. Furthermore, the percentages of stem cell-generated neurons, astrocytes, and oligodendrocytes were markedly lower in the cultures prepared from the Igf-I(-)/- mice compared with those of Igf-I(+/+). Concordantly, lack of IGF-I resulted in abnormal formation of the olfactory bulb mitral cell layer and altered radial glia morphology. These results support the presence within the embryonic mouse olfactory bulb of stem cells with specific requirements for insulin-related growth factors for proliferation or differentiation. They demonstrate that IGF-I is an endogenous factor regulating the differentiation of stem and other precursor cells within the olfactory bulb.

Nicotine-induced enhancement of glutamatergic and GABAergic synaptic transmission in the mouse amygdala

Presynaptic nicotinic acetylcholine receptors (nAChRs) are thought to mediate some of the cognitive and behavioral effects of nicotine. The olfactory projection to the amygdala, and intra-amygdaloid projections, are limbic relays involved in behavioral reinforcement, a property influenced by nicotine. Co-cultures consisting of murine olfactory bulb (OB) explants and dispersed amygdala neurons were developed to reconstruct this pathway in vitro. Whole cell patch-clamp recordings were obtained from amygdala neurons contacted by OB explant neurites, and spontaneous and evoked synaptic currents were characterized. The majority of the 108 innervated amygdala neurons exhibited glutamatergic spontaneous postsynaptic currents (PSCs), 20% exhibited GABAergic spontaneous PSCs, and 17% exhibited both. Direct extracellular stimulation of OB explants elicited glutamatergic synaptic currents in amygdala neurons. Antibodies to nAChR subunits co-localized with an antibody to synapsin I, a presynaptic marker, along OB explant processes, consistent with the targeting of nAChR protein to presynaptic sites of the mitral cell projections. Hence, we examined the role of presynaptic nAChRs in modulating synaptic transmission in the OB-amygdala co-cultures. Focal application of 500 nM to 1 microM nicotine for 5-60 s markedly increased the frequency of spontaneous PSCs, without a change in the amplitude, in 39% of neurons that exhibited glutamatergic spontaneous PSCs (average peak fold increase = 125.2 +/- 33.3). Nicotine also enhanced evoked glutamatergic currents elicited by direct stimulation of OB explant fibers. Nicotine increased the frequency of spontaneous PSCs, without a change in the amplitude, in 35% of neurons that exhibited GABAergic spontaneous PSCs (average peak fold increase = 63.9 +/- 34.3). Thus activation of presynaptic nAChRs can modulate glutamatergic as well as GABAergic synaptic transmission in the amygdala. These results suggest that behaviors mediated by olfactory projections may be modulated by presynaptic nAChRs in the amygdala, where integration of olfactory and pheromonal input is thought to occur.

Developmental changes in neurotensin and its metabolites in the neonatal rat

Neurotensin-like immunoreactivity (NT-LI) was measured in the di-, tel- and mesencephalon of rats from embryonic day 15 (E15) through birth ( approximately E22) until postnatal day 5 (P5) using radioimmunoassay (RIA) and an N-terminal directed polyclonal antibody. NT-LI and NT metabolite-like immunoreactivities (NT 1-8, NT 1-10, NT 1-11 and NT 1-12-LI) were also similarly determined using high performance liquid chromatography (HPLC) coupled with RIA. NT-LI was low at E15 but increased to peak levels at around E20 or birth in the di- and telencephalon, after which the levels declined. Similar, but lower, changes were observed with NT 1-10-LI but not other metabolites while much lower NT-LI and metabolites were observed in the mesencephalon where no transitory changes occurred. The changes in neonatal rat brain NT and metabolites are discussed with respect to the possible neonatal trophic roles of these peptides.

An olfactory sensory map develops in the absence of normal projection neurons or GABAergic interneurons

Olfactory sensory neurons expressing a given odorant receptor project to two topographically fixed glomeruli in the olfactory bulb. We have examined the contribution of different cell types in the olfactory bulb to the establishment of this topographic map. Mice with a homozygous deficiency in Tbr-1 lack most projection neurons, whereas mice with a homozygous deficiency in Dlx-1 and Dlx-2 lack most GABAergic interneurons. Mice bearing a P2-IRES-tau-lacZ allele and deficient in either Tbr-1 or Dlx-1/Dlx-2 reveal the convergence of axons to one medial and one lateral site at positions analogous to those observed in wild-type mice. These observations suggest that the establishment of a topographic map is not dependent upon cues provided by, or synapse formation with, the major neuronal cell types in the olfactory bulb.

Neurotensin and neuroendocrine regulation

More than two decades of research indicate that the peptide neurotensin (NT) and its cognate receptors participate to a remarkable extent in the regulation of mammalian neuroendocrine systems, potentially at multiple levels in a given system. NT-synthesizing neurons appear to exert a direct or indirect stimulatory influence on neurosecretory cells that synthesize gonadotropin-releasing hormone, dopamine (DA), somatostatin, and corticotropin-releasing hormone (CRH). In addition, context-specific synthesis of NT occurs in hypothalamic neurosecretory cells located in the arcuate nucleus and parvocellular paraventricular nucleus, including distinct subsets of cells which release DA, CRH, or growth hormone-releasing hormone into the hypophysial portal circulation. At the level of the anterior pituitary, NT stimulates secretion of prolactin and occurs in subsets of gonadotropes and thyrotropes. Moreover, circulating hormones influence NT synthesis in the hypothalamus and anterior pituitary, raising the possibility that NT mediates certain feedback effects of the hormones on neuroendocrine cells. Gonadal steroids alter NT levels in the preoptic area, arcuate nucleus, and anterior pituitary; adrenal steroids alter NT levels in the hypothalamic periventricular nucleus and arcuate nucleus; and thyroid hormones alter NT levels in the hypothalamus and anterior pituitary. Finally, clarification of the specific neuroendocrine roles subserved by NT should be greatly facilitated by the use of newly developed agonists and antagonists of the peptide.

Early onset of the rat olfactory bulb projections

Using the fluorescent carbocyanine tracer DiI, we examined in detail the early development of the projections emanating from the rat olfactory bulb. The study commenced at embryonic day 13 when the first fibres can be detected and ended at embryonic day 20, when all major fibre systems have been established. The first axons arising from the prospective olfactory bulb area are seen at embryonic day 13. Labelled fibres are provided with elaborate axonal growth cones advancing through the ventrolateral part of the telencephalic vesicle. At embryonic day 14, while the main fibre tract has not developed much further, some isolated fibres are located quite distally from the prospective olfactory bulb. These early fibres apparently course within a narrow cell-free space that extends caudally along the ventrolateral part of the telencephalic vesicle. At embryonic day 15, a number of labelled fibres form a compact bundle, corresponding to the lateral olfactory tract, that ultimately reaches the prospective primary olfactory cortex. The fibres do not stop growing, but continue to extend caudally at embryonic day 17. The results of this study provide new information on the development of axonal tracts in the olfactory system. We show that the olfactory tract projection develops earlier than the morphological appearance of the olfactory bulbs. This suggests that the early development of olfactory projections might not depend on the arrival of the olfactory epithelium axons and thus, could be governed by factors intrinsic to the neurons and/or cues present in the target environment.