title: Novel subdomains of the mouse olfactory bulb defined by molecular heterogeneity in the nascent external plexiform and glomerular layers.
abstract: BACKGROUND
  In the mouse olfactory system, the role of the olfactory bulb in guiding olfactory sensory neuron (OSN) axons to their targets is poorly understood. What cell types within the bulb are necessary for targeting is unknown. What genes are important for this process is also unknown. Although projection neurons are not required, other cell-types within the external plexiform and glomerular layers also form synapses with OSNs. We hypothesized that these cells are important for targeting, and express spatially differentially expressed guidance cues that act to guide OSN axons within the bulb.
  
  
  RESULTS
  We used laser microdissection and microarray analysis to find genes that are differentially expressed along the dorsal-ventral, medial-lateral, and anterior-posterior axes of the bulb. The expression patterns of these genes divide the bulb into previously unrecognized subdomains. Interestingly, some genes are expressed in both the medial and lateral bulb, showing for the first time the existence of symmetric expression along this axis. We use a regeneration paradigm to show that several of these genes are altered in expression in response to deafferentation, consistent with the interpretation that they are expressed in cells that interact with OSNs.
  
  
  CONCLUSIONS
  We demonstrate that the nascent external plexiform and glomerular layers of the bulb can be divided into multiple domains based on the expression of these genes, several of which are known to function in axon guidance, synaptogenesis, and angiogenesis. These genes represent candidate guidance cues that may act to guide OSN axons within the bulb during targeting.
authors.affiliation: Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA. eow1@cornell.edu <eow1@cornell.edu>
authors.forename: Eric O
authors.initials: EO
authors.lastname: Williams
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Xiao
authors.forename: Heather M
authors.initials: HM
authors.lastname: Sickles
authors.forename: Paul
authors.initials: P
authors.lastname: Shafer
authors.forename: Golan
authors.initials: G
authors.lastname: Yona
authors.forename: Jean Y H
authors.initials: JY
authors.lastname: Yang
authors.forename: David M
authors.initials: DM
authors.lastname: Lin
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics; D004622:Embryo, Mammalian; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018740:Genetic Heterogeneity; D051379:Mice; D035683:MicroRNAs; D042282:Microdissection; D009830:Olfactory Bulb / Q000196:embryology*; D018034:Olfactory Receptor Neurons / Q000196:embryology*; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D020825:T-Box Domain Proteins
chemical_list: D004268:DNA-Binding Proteins; D035683:MicroRNAs; D020825:T-Box Domain Proteins; C492271:Tbr1 protein, mouse