Olfactory system and MB development

1. Olfactory system and MB development

2. 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

4. 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

5. Odorant receptor (OR) genes: share as little as 20% identity

6. Drosophila Ordorant Receptors (DOR)

8. DOR expressions are conserved among individuals

9. DOR genes are expressed in distinct subsets of antennal neurons

10. 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

11. Proneural genes in olfactory sensilla

12. 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

13. 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

14. order degrading enzyme order binding protein sensory neuron membrane protein

15. 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

16. Distribution of functional types of basiconica sensilla

17. Three types of large basiconic sensilla

18. 18 classes of ORNs within eight functional types of basiconica sensilla (ab1, ab2, ab3 are large basiconica sensilla)

19. Mapping Or 22a/b expression in ab3 sensilla

22. Drosophila olfactory system

24. Neurons expressing a given DOR gene converge on one or two spatially invariant antennal lobe glomeruli DOR-GAL4, UAS-nsyb-GFP

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

26. Targeting specificity of ORN to glomeruli does not depend on Or genes expressed UAS-GFP; Or22a-GAL4 halo mutants (Or22a,b deleted) wild type UASGFP; halo; Or22a-GAL4 UAS-Or47a UAS-Or33c

27. Spatial maps of ORNs and glomeruli

28. Projection neurons

29. MARCM to generate single cell or NB clones

30. Targeting specificity of adPNs and lPNs to glomeruli ~50 ~35

33. Drosophila olfactory system

34. The adult mushroom body: center for learning and memory 2,500 neurons

35. Home work Principle and application of the MARCM technique

36. MB (2500 neurons) derived from 4 NBs

37. 19 GAL4 strains reveal four folds of lineages in MB Hydroxyurea ablation of three NBs (only one left) gives rise to all MB structure WT HU

38. MARCM

39. Development of the MB

40. g neuron pruning

41. TGF-b signaling activates steroid hormone receptor expression

42. Expressions of Acj6 and Dfr, two POU domain homeobox proteins

43. Misexpression of Dfr in acj6 mutant clones reroutes DL1 innervation to another glomerulus