Transcript Genomics of sensory systems - University of Maryland

Lecture 16 : Hearing
Fain ch 6
10/28/09
Midterm project
 Dr.
Payne is in search of -
# trp channels in inverts
Is there conservation of pore - Ca+2
selectivity
Evolutionary constraint across inverts
All inverts have the same Ca+2 selectivity
All have D621
There is more than one type of invert Trp
Might differ in pore region, D621
Align w/ Drosophila Trp
Tree
TrpN
TrpV
TrpM
TrpC
TrpA
Trp M
D
Trp C
How should we name sequences
for big tree?
 Dme
= First letter of Genus , 1st two of
species
 Add last four or five numbers of gene #
 Gi|123943828|
What do you want for an
outgroup?
Possibilities:
Make fasta file with all of your
sequences + Dr Paynes limulus
+ outgroup + Drosophila trp +
trpl + trpgamma + Human trpC1
and 3
What data should each of you
give him?
 Table
of genes - acc# - Trp box1 seq pore site (5 AA) - site 621
 Notes - ex. Missing pore region ignored
 Tree w/ TrpM, N, V , A
How should we present data to
Dr. Payne next week?
 Tree
 For TrpCs label pore site and Trp box1
To do list
 Today
- Fasta file with renamed seqs
 Next week - one ppt slide with tree
(TrpCs labeled with pore)
 Stuff emailed to Dr Payne
Wait till after class on Wed
Monday
I
will be visiting Duke to give a seminar
 Dr. Chris Hofmann will give a lecture on
vertebrate vision and my favorite cichlid
fish
 He can answer questions on
phylogenetics
Questions
1.
2.
3.
4.
What is the structure of the ear?
Why are hair cells important?
How do hair cells transmit signals?
What molecules are important?
Hearing is a key sense

Detect sound
Intensity
Frequency
Direction
Ear
Vestibular organs

Semicircular canals
Anterior
Posterior
Lateral

Anterior
Posterior
Lateral
Otolith organs
Utriculus
Sacculus
Lagena (sometimes)
Hair cells in ampullae
Hair cells in ampulae

All hair cells point
same way in a given
canal

Detect fluid or otolith
motion
Fig 6.15
Vestibular

Endolymph
High in Ca+2 K+

Depolarize when K+
enters through hair
cell channels
Sensing head motion
Fig 6.16
Hair cells in semicircular canals

Detect position and
movement of head
Hair cells detect
motion in different
directions
Fig 6.1
Neuromast with cupula
Cupula - gelatinous covering
Ear
Middle ear
Inner ear

Semicircular canals

Cochlea
Cochlea has hair cells supported by
basilar membrane
Basilar membrane responds to high, med and low freq as
move down the cochlea
Organ of Corti
15,000 hair cells in mammals
Fig 6.18
Hair cells in cochlea

Inner hair cells

Organ of Corti on
basilar membrane

Outer hair cells
Cochlear hair cells have lost kinocilium
Organ of Corti
Tectorial membrane
Stereocilia bathed by endolymph: K+ rich
Rest of cochlea bathed in perilymph Na+ rich
Fig 6.18
Frequency
response


Frequency response differs down membrane
Actual freq response is narrower than expect
Cochlear amplifier


Inner hair cells make 90-95%
of neural connections
Outer hair cells
Tune frequency response

Change shape in response
to sound
Depolarize - shorten
Hyperpolarize - lengthen


Motion conferred by protein
called prestin
Moves Organ of Corti up and
accentuates basilar
membrane motion
Hair cells
Electrical resonance



Cells have frequencies
at which respond
maximally to oscillating
potential
Response to sounds at
resonant frequency will
be amplified
Cells differ in electrical
response down cochlea
Difference in Ca+2 gated K+
channels
Cell response
 Mechanosensation
- depolarize
 Opens voltage gated Ca+2 channels depolarize and let in Ca+2
 Ca+2 triggers Ca+2 gated K+ channels hyperpolarize
 Density of channels and properties of
Kca channels will “tune” resonant
frequency
Electrical resonance



Cells have frequencies
at which respond
maximally to oscillating
potential
Response to sounds at
resonant frequency will
be amplified
Cells differ in electrical
response down cochlea
Difference in Ca+2 gated K+
channels