Sall3 correlates with the expression of TH in mouse olfactory bulb

Characterization by Gene Expression Analysis of Two Groups of Dopaminergic Cells Isolated from the Mouse Olfactory Bulb

The olfactory bulb (OB) is one of two regions of the mammalian brain which undergo continuous neuronal replacement during adulthood. A significant fraction of the cells added in adulthood to the bulbar circuitry is constituted by dopaminergic (DA) neurons. We took advantage of a peculiar property of dopaminergic neurons in transgenic mice expressing eGFP under the tyrosine hydroxylase (TH) promoter: while DA neurons located in the glomerular layer (GL) display full electrophysiological maturation, eGFP+ cells in the mitral layer (ML) show characteristics of immature cells. In addition, they also display a lower fluorescence intensity, possibly reflecting different degrees of maturation. To investigate whether this difference in maturation might be confirmed at the gene expression level, we used a fluorescence-activated cell sorting technique on enzymatically dissociated cells of the OB. The cells were divided into two groups based on their level of fluorescence, possibly corresponding to immature ML cells and fully mature DA neurons from the GL. Semiquantitative real-time PCR was performed to detect the level of expression of genes linked to the degree of maturation of DA neurons. We showed that indeed the cells expressing low eGFP fluorescence are immature neurons. Our method can be further used to explore the differences between these two groups of DA neurons.

Transcriptome comparison identifies potential biomarkers of spine and skull base chordomas

Chordomas are rare, slowly growing, locally aggressive bone neoplasms that arise from embryonic remnants of the notochord, showing dual epithelial-mesenchymal differentiation. The high plasticity probably is the main reason for the high variety in phenotypes of chordoma, from its high heterogeneity on a cellular level to its subtype variations depending on tissue location, with its potential to develop from an inactive quiescent form to an aggressive cancer with extreme adaptability and resistance to drugs and other treatments. Gene expression profiles of formalin-fixed, paraffin-embedded skull chordoma, spine chordoma, and normal tissue specimens were generated and compared. Using strict criteria, we identified 222 differentially expressed transcripts unique to skull base chordoma, 261 unique to spine chordoma, and 192 common to both chordoma subtypes. Further analysis of these three groups of transcripts allowed the selection of three subsets of highly differentially expressed genes as potential biomarkers, disease drivers, and therapeutic targets in both chordoma subtypes. Immunohistochemistry revealed LMX1A to be dominant in skull base chordoma, SALL3 to be unique to spine chordoma, and T to be common to both chordoma subtypes. In both chordoma subtypes, the genes with the highest expression were predominantly development-related genes, mostly transcription factors. Our findings indicate that these developmental genes play important oncogenic roles in chordoma, mainly causing high plasticity and resistance to therapy in both these cancer subtypes but also determining their differentiation status and proliferation activity, pointing to features expected of heterogeneous stem cell-like tissues with similarities to their notochord origins.

Determination of the connectivity of newborn neurons in mammalian olfactory circuits

The mammalian olfactory bulb is a forebrain structure just one synapse downstream from the olfactory sensory neurons and performs the complex computations of sensory inputs. The formation of this sensory circuit is shaped through activity-dependent and cell-intrinsic mechanisms. Recent studies have revealed that cell-type specific connectivity and the organization of synapses in dendritic compartments are determined through cell-intrinsic programs already preset in progenitor cells. These progenitor programs give rise to subpopulations within a neuron type that have distinct synaptic organizations. The intrinsically determined formation of distinct synaptic organizations requires factors from contacting cells that match the cell-intrinsic programs. While certain genes control wiring within the newly generated neurons, other regulatory genes provide intercellular signals and are only expressed in neurons that will form contacts with the newly generated cells. Here, the olfactory system has provided a useful model circuit to reveal the factors regulating assembly of the highly structured connectivity in mammals.

Adult Born Olfactory Bulb Dopaminergic Interneurons: Molecular Determinants and Experience-Dependent Plasticity

The olfactory bulb (OB) is a highly plastic brain region involved in the early processing of olfactory information. A remarkably feature of the OB circuits in rodents is the constitutive integration of new neurons that takes place during adulthood. Newborn cells in the adult OB are mostly inhibitory interneurons belonging to chemically, morphologically and functionally heterogeneous types. Although there is general agreement that adult neurogenesis in the OB plays a key role in sensory information processing and olfaction-related plasticity, the contribution of each interneuron subtype to such functions is far to be elucidated. Here, we focus on the dopaminergic (DA) interneurons: we highlight recent findings about their morphological features and then describe the molecular factors required for the specification/differentiation and maintenance of the DA phenotype in adult born neurons. We also discuss dynamic changes of the DA interneuron population related to age, environmental stimuli and lesions, and their possible functional implications.