Development of sense organs

Development of sense organs

1. Senses

   • General and special senses
   • Sensory neuron origins
     • Neural crest e.g. DRG
     • Neural tube e.g. retina
     • Placodes, e.g. olfactory epithelium, some cranial nerves (e.g.V)

2. C. elegans

   • Range of mechanoreceptors
     • e.g. gentle body touch, harsh body touch
       • Numerous touch-insensitive mutants screened
     • Touch cell lineage
       • Q cell lineage
         • Q cell – Q1a and Q1p
           • Q1p gives rise to GBT cell and an interneuron
         • Control of Q cell division
           • Loss of MEC-3 transforms touch cell
             • UNC-86 induces MEC-3
               • UNC-86 and MEC-3 combine to induce touch cell-specific genes
                 • E.g. involved in
                   • 15 protofilament microtubules
                   • specialised ECM
           • A form of lineage-dependent differentiation – an intrinsic blueprint
       • UNC-86 turned on in Q1p
       • Loss UNC-86 gives loss of touch cell

3. Drosophila

   • Mechanoreceptors
     • Numerous types of sensory structures
       • e.g. mechanosensory
       • Derived from sensory organ precursors (SOP)
         • SOPs for chordotonal organs express atonal
         • SOPs for external receptors express ct
     • Single innervated sensilla
       • NUMB is asymmetrically distributed between SPIIb and SPIIa
         • NUMB inhibits NOTCH pathway
           • Low NOTCH activity required for neural fate
       • To some extent lineage-dependent development
   • The drosophila eye
     • consists of ~800 ommatidia
     • 8 photoreceptors R1-8
     • 12 accessory cells
     • Atonal
       • During OM development, atonal expression is ↑ in R8 by posterior tip Hh
         • Atonal and R8 (Hh+) required for OM formation
           • Activates Notch and Delta producing spaced R8 cells
       • Interaction cascade
         • Subsequent OM development depends on cell-cell interaction
           • e.g. Bride of Sevenless on R8 causes R7 to become a photoreceptor and not a cone cell
         • Development of stereotypy by competition and rules rather than strict predetermination

4. Vertebrate

   • vertebrate eye
     • Retina - laminar structure
     • Derived from neural and non-neural ectoderm
       • Requires expression of Pax-6 (eyeless)
     • Ventricular progenitors produce types in sequence
       • Not separate progenitors
         • Neurogenesis of ganglion cells first
     • Cell production influenced by environment
   • The ear
     • develops from the otic placode
       • Forms into otic pit then otic vesicle (otocyst)
       • VIII ganglion is placodal
     • Hair cell development
       • Hair cell development regulated by cell- cell interactions
         • High notch activation = supporting cells. Low notch activation = hair cells.
           • Retinoic acid and thyroid hormone involved later
       • Hair bundle formation
         • Poorly understood
         • In human deaf/blindness Usher Ib myosin VII a altered
           • Ushers Id and If involve cadherins
   • Olfactory neurons
     • Olfactory receptor cells and secretory cells from basal cells
       • Form throughout life
     • Olfactory bulb neurons generated (at least in part) from SVZ
       • Rostral migratory stream
   • Lateral line
     • The lateral line detects water motion in fish
       • Like inner ear sensory systems
         • Contain sensory neurons -neuromasts
     • Develops from placodes
       • Primordial region of placode migrates towards the tail
         • Deposits neuromasts as it moves

Images and files in the map