Wiring the olfactory system

Question 1

olfactory epithelium organisation

Answer 1

nasal cavity contains cilia
sustentacular cells provide metabolic/physical support
OSNs (mature and immature)
GBCs (globose basal cells) - stem cells

Question 2

olfactory epithelium neurogenesis

Answer 2

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

Question 3

OSN lifespan

Answer 3

2-3 months
continued production
vulnerable to infection because exposed to the extracellular environment

Question 4

OSN maturation

Answer 4

iOSNs migrate towards nasal cavity to become mature
mature OSNs fully functional in 5-7 days express OMP (marker of mature OSNs)

Question 5

one receptor-one neuron hypothesis

Answer 5

each OSN expresses one OR gene
~1100 OR genes in mice
OR located on cilia

Question 6

single cell transcriptomics

Answer 6

identify the OR types
Fluidigmc1: capture, cDNA generation, PCR amplification
RNA seq of single OSNs
n=21

Question 7

sequencing of ORs

Answer 7

early iOSNs have many ORs
late and mature OSNs express only 1 OR

Question 8

OSN axon projections

Answer 8

all axons project to the glomerulus (have dendrites) Each OSN projects to 1 glomerulus (homogenous)
glomerulus located in the OB

Question 9

OSN axon guidance

Answer 9

E12 - initial outgrowth
OP = olfactory placode contains migratory mass (+GnRH hypothalamic neurons)
axons reach E13-17

Question 10

markers

Answer 10

GAP43 - immature neuronal marker
MAP2 - dendritic marker
dendrites of OSNs act as a stop signal from growing into OB

Question 11

DV mapping and axon guidance

Answer 11

coarse topography
dorsal nose - dorsal OB
ventral nose - ventral OB

Slit1 & Robo - D
Sema3F ventral to dorsal

Question 12

what does ML mapping use

Answer 12

IGF-1

Question 13

AP mapping

Answer 13

P2 and M12 - ORs
P2 given 12 OR coding region
shift towards M12

increased cAMP = P
decreased cAMP = A

Question 14

how does each OR activate OSN

Answer 14

each OR does not depend on odorant binding
each OR has intrinsic ability to activate OSN

Question 15

how to find right position on the OB

Answer 15

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

Question 16

experiment to determine location of the glomerulus

Answer 16

in vitro
remove OB, glomeruli form outside OB, OSNs grow in PFC, visual cortex where OB used to be , glomerulus formed

Question 17

glomerular segregation

Answer 17

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)

Question 18

UNO

Answer 18

unilateral naris occlusion upregulates Kirrel2 (blocks sensory activity)

Question 19

critical period

Answer 19

periods where the developing brain is plastic
axons compete, mapping axons, kirrels cause binding , Ephs are repellants

Question 20

glutamatergic OB circuits

Answer 20

MCs/TCs - glutamatergic input neurons

Question 21

MC development

Answer 21

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)

Question 22

OSN to OB synapse

Answer 22

presynaptic membrane - Sema7a
postsynaptic membrane - PlxnC1

Question 23

experiment to find out where OB interneurons emerge

Answer 23

transplant dye in MGE at E13.5 - No OB interneurons
transplant dye in LGE at 13.5 - OB interneurons present

Question 24

2 sites of adult neurogenesis

Answer 24

OSNs in the olfactory epithelium (nose)
ob interneurons

Question 25

immature adult interneurons vs mature interneurons

Answer 25

immature adult interneurons respond more strongly to odorants and have more dendritic spines

Question 26

embryonic interneurons

Answer 26

E12/18
contain AIS