Wiring the olfactory system Flashcards
olfactory epithelium organisation
nasal cavity contains cilia
sustentacular cells provide metabolic/physical support
OSNs (mature and immature)
GBCs (globose basal cells) - stem cells
olfactory epithelium neurogenesis
GBC self renew (Sox2/pax6)
GBC mpp (increase in Ascl1 - proneural gene)
GBC TA-OSN (transit amplifying cell) Acl1 Sox2 Pax6
GBC INP (increase neurog1/d1)
downregulated progenitor cells:
differentiating OSNs
OSN lifespan
2-3 months
continued production
vulnerable to infection because exposed to the extracellular environment
OSN maturation
iOSNs migrate towards nasal cavity to become mature
mature OSNs fully functional in 5-7 days express OMP (marker of mature OSNs)
one receptor-one neuron hypothesis
each OSN expresses one OR gene
~1100 OR genes in mice
OR located on cilia
single cell transcriptomics
identify the OR types
Fluidigmc1: capture, cDNA generation, PCR amplification
RNA seq of single OSNs
n=21
sequencing of ORs
early iOSNs have many ORs
late and mature OSNs express only 1 OR
OSN axon projections
all axons project to the glomerulus (have dendrites) Each OSN projects to 1 glomerulus (homogenous)
glomerulus located in the OB
OSN axon guidance
E12 - initial outgrowth
OP = olfactory placode contains migratory mass (+GnRH hypothalamic neurons)
axons reach E13-17
markers
GAP43 - immature neuronal marker
MAP2 - dendritic marker
dendrites of OSNs act as a stop signal from growing into OB
DV mapping and axon guidance
coarse topography
dorsal nose - dorsal OB
ventral nose - ventral OB
Slit1 & Robo - D
Sema3F ventral to dorsal
what does ML mapping use
IGF-1
AP mapping
P2 and M12 - ORs
P2 given 12 OR coding region
shift towards M12
increased cAMP = P
decreased cAMP = A
how does each OR activate OSN
each OR does not depend on odorant binding
each OR has intrinsic ability to activate OSN
how to find right position on the OB
1) stochastic OR establishes identity
2) OR activates PERK arm of the unfolded protein response (UPR)
3) Ddit3 (TF) converts UPR levels into axon guidance cues
experiment to determine location of the glomerulus
in vitro
remove OB, glomeruli form outside OB, OSNs grow in PFC, visual cortex where OB used to be , glomerulus formed
glomerular segregation
like axons coalesce and unlike away move away (homotypic/heterotypic adhesion) kirrel 2/3 remain segregated
cells expressing MOR28 (OR) show a lack of Kirrel2
each OSN has a different code for cell adhesion molecules
EphrinA5/ephA5 used for repulsion (causes segregation)
UNO
unilateral naris occlusion upregulates Kirrel2 (blocks sensory activity)
critical period
periods where the developing brain is plastic
axons compete, mapping axons, kirrels cause binding , Ephs are repellants
glutamatergic OB circuits
MCs/TCs - glutamatergic input neurons
MC development
born in the proliferating zone
present around E12 in rodent
stages: migration, outgrowth, pruning1/2, mature
MC sends out apical dendrites, dendrites initially target multiple neighbouring glomeruli
then refine to a single glomerulus (should be in reach)
OSN to OB synapse
presynaptic membrane - Sema7a
postsynaptic membrane - PlxnC1
experiment to find out where OB interneurons emerge
transplant dye in MGE at E13.5 - No OB interneurons
transplant dye in LGE at 13.5 - OB interneurons present
2 sites of adult neurogenesis
OSNs in the olfactory epithelium (nose)
ob interneurons
immature adult interneurons vs mature interneurons
immature adult interneurons respond more strongly to odorants and have more dendritic spines
embryonic interneurons
E12/18
contain AIS
