Q 29 on Exam I: In the neural tube, BMP4 is to Shh as:
a) Dpp is to Sog
b) Engrailed is to Otx2
c) Hoxa2 is to retinoic acid
d) Hes1 is to Hes5
e) Noggin is to BMP
-Essentially, question was formulated to illustrate opposing DV gradients in development of the body axis & nerve
cord/spinal cord.
-I will give 2 pts to anyone who had points deducted from their
grade IF they can provide a better answer to the question and
clearly state the rationale for the alternative answer.
In flies, dpp= BMP
(blocks neural), &
sog= noggin/chordin
(promotes neural)
Optional short presentations in class April 25th:
-research a human neurological disorder and discuss in the
context of developmental neurobiology
-give a short 5-10 min slide presentation
-write a 5-page report on how altered neural development
may contribute/contributes to the disease, and which form of
therapy you would recommend
Examples:
-Huntington’s chorea
-Alzheimer’s disease
-Major depressive disorder
-Schizophrenia
-Traumatic brain injury
Retinal cell outgrowth on tectal membranes expressing EphrinA
ligands: no temporal growth
EphA2-/-; A5-/- RGCs randomly project to tectum; ectopic
EphA3 R causes anterior shift of projections
Gradients of both ligand (tectum) and receptor (axon) establish
map
Ephrins & EphR gradients shape the retinotectal map across
species
Retinal axon outgrowth is promoted at low levels of Ephrin-A2
Repulsive EphA signals guide retina N-T, tectum A-P axon
mapping; attractive EphB signals guide D-V, D-V axon mapping
EphrinA ligands activate EphA receptors, & EphrinBs activate
EphB receptors
High EphA (T ret) low EphrinA (A tect); high EphB (V ret)
high EphrinB1 (M tect)
EphrinB-EphB forward & reverse signaling in D-V retinotectal map
The tectum/colliculus develops at the border between midbrain
& hindbrain
Grafting experiment demonstrates a midbrain-hindbrain organizer
Fgf8: a potent signal within the MB-HB organizer
Fgf8 bead duplicates the organizer region & mesencephalon in
the diencephalon
Olfactory receptor neurons synapse with 2nd order neurons in the
glomerulus
Each glomerulus in the olfactory bulb receives neurons of only
one subtype
Brain 
Nose 
Topographic map in the olfactory epithelium is random (grouped
by odorant)
Genetic labeling of an olfactory receptor revealed convergence on
one glomerulus
P2 receptor+
cells= blue
Olfactory receptors are expressed on both dendrites and axons
olfactory
epithelium
olfactory
bulb (brain)
Odorant receptor protein is expressed on both dendrites and axons of olfactory sensory neurons. A and B.
Staining of mouse olfactory epithelium with antibodies to two different particular odorant receptors
(one labelled in red, the other in green). C. and D. Staining of mouse olfactory bulb with the same antibodies.
Scale bars, 10mm. (From Barnea et al., 2004)
No defined regional specificity in the nasal epithelium for olfactory
neuron subclasses
The olfactory neuron subtype & glomerular target is defined by
its receptor
P2 receptor deletion causes loss of glomerular targeting
Swapping M71 in place of the P2 receptor leads to glomerulus “X”
targeting
Other guidance factors are needed for precise glomerular targeting
Fine-tuning synaptic connectivity: A) reducing # afferents/
arborization to multiple target cells
Fine-tuning neural connectivity: B) removing redundant inputs
(afferents) to the same target cell
In maturing neural circuits: C) remove excess synapses on same
neuron
Synaptic maturation also involves altering # synapses from a
specific presynaptic neuron (afferent projection)
Dual innervation of muscle by motor neurons is lost postnatally
Multiple innervations at the immature neuromuscular junction
Electrophysiological test for number of convergent inputs
*quantal increases
in PSP amplitude
 estimate of input #
The number of convergent innervations decreases with maturity