olfactory system and mb development
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Olfactory system and MB development. The Nobel Prize in Physiology or Medicine 2004 "for their discoveries of odorant receptors and the organization of the olfactory system". Richard Axel Linda B. Buck. Olfactory receptor & different strategy.

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The Nobel Prize in Physiology or Medicine 2004

"for their discoveries of odorant receptors and the organization of the olfactory system"

Richard Axel Linda B. Buck

olfactory receptor different strategy
Olfactory receptor & different strategy
  • Odorous ligands trigger G protein-coupled receptors
  • ~350 in human, ~1000 in C. elegans and mouse
  • 60 ORs in D.melanogaster, with 1300 receptor neurons in flies.
  • there are ~60 gustatory receptors (GRs) in flies, sensing sugar (attractant), bitter compound (repellent), salt and water.

C. elegans only 16 pairs sensory cell. Each with

multiple kinds of receptor

mice 2,000,000 receptor neurons. Each with

one receptor

olfactory sensilla
Olfactory Sensilla

a: antenna, p:maxillary

B:basiconic (L and S, ~200), T:trichoid, C:coeloconic

1200 ORNs in antenna and 120 ORNs in maxillary pulp


Fig. 1 The insect antenna typically bears between several hundred and some thousand sensillar hairs, depending on the species, which are depicted on the left. Each sensillum contains between 1 and 4 ORNs (red and dark blue, respectively). These are bipolar neurons which, on one end, extend a dendrite that is bathed in sensillar lymph and interacts with odorants and on their other end project axons that terminate in the AL, where olfactory information is processed. ORNs are embedded in a layer of support cells (light green) that secrete proteins such as OBPs (orange and light blue) into the sensillum lymph. Odorants can enter the sensillum lymph via pores in the cuticle and cross the lymph in a hitherto still debated way that may involve OBPs as transport vehicles. Subsequent odorant-OR binding takes place along the dendrite of an ORN and may activate a heterotrimeric G-protein to target

one or more of many possible effectors and finally gates ion channels thereby creating APs


Expression of Or22a/b in the Dendrites of ORNs in Large Basiconica Sensilla

(D) Crosssection labeled with anti-22a/b antibody. Granules of immunogold are visible in the dendrites (labeled D).

(E) Longitudinal section labeled with anti-22a/b antibody. Labels indicate the following: C, cuticle; D, dendrite; P, pore; and SL, sensillum lymph.

(F) An example of a different morphological subtype of s. basiconica, which shows no labeling with anti-22a/b antibody.

Neuron, Vol. 37, 827–841, 2003


order degrading enzyme

order binding protein

sensory neuron

membrane protein


Fig. 2 Hypothetical model incorporating recent insights about

molecular interactions in the lumen and at the dendritic membrane

of an insect ORN. Odorants entering through cuticular pores are

immediately loaded onto OBPs that transport chemicals to

conventional ORs (ORx) and also protect them from degradation

by ODEs (yellow). Transport of odorants is directed by a specific

OBP receptor that is either constituted by (1) the conventional OR

(interacting with the red odorant/ OBP) or (2) by a different

molecule (SNMP?; interacting with the black odorant/ blue OBP),

which may physically interact with the conventional and/or 83b

family OR. SNMPs are candidate molecules that may function as

OBP receptors. Conventional ORs physically interact with a highly

conserved 83b family OR which is expressed in a majority of

ORNs. OR83b family proteins facilitate trafficking of conventional

ORs to the dendritic membrane and may contribute to signal

transduction. A complex that consists of a conventional OR, an

Or83b family protein and possibly additional molecules, may be

required to fully activate a heterotrimeric G-protein. Little is

known about the signal transduction events and ion channels that

are involved in the generation of APs in insects. Possible G protein

effectors involve phospholipases such as PLCb

18 classes of ORNs within eight functional types of basiconica sensilla (ab1, ab2, ab3 are large basiconica sensilla)
Neurons expressing a given DOR gene converge on one or two spatially invariant antennal lobe glomeruli


Olfactory neurons expressing a given DOR gene synapse with both contralateral and ipsilateral glomeruli

Targeting specificity of ORN to glomeruli does not depend on Or genes expressed


halo mutants (Or22a,b deleted)

wild type

UASGFP; halo; Or22a-GAL4



home work

Home work

Principle and application of the MARCM technique

19 gal4 strains reveal four folds of lineages in mb
19 GAL4 strains reveal four folds of lineages in MB

Hydroxyurea ablation of three NBs (only one left) gives rise to all MB structure