of the Max - MDC

Genetic Analysis of
Neural Circuits
Alistair N. Garratt
(Helmholtz Fellow)
We employ mice as model systems to characterize the role
of specific genes in neural circuits through classical and
conditional (tissue-specific) gene inactivation.
Nociceptive tuning by the receptor tyrosine
kinase c-Kit
Christina Frahm, Carola Griffel
The molecular mechanisms regulating the sensitivity of sensory
circuits to environmental stimuli are still poorly understood.
We have discovered a central role for Stem Cell Factor
(SCF) and its receptor, c-Kit, in tuning the responsiveness of
sensory neurons to natural stimuli. For this, we have performed
the first analysis of nervous system phenotypes in mice
lacking a functional SCF/c-Kit signaling system. We employed
c-Kit mutants in which the lethal anemia had been rescued
by an erythropoietin-transgene. C-Kit mutant mice displayed
profound thermal hypoalgesia, attributable to a marked
elevation in the thermal threshold and reduction in spiking
rate of polymodal heat-sensitive C-fiber nociceptors (in
collaboration with Gary Lewin, MDC). Acute activation of c-
Kit by its ligand, SCF, resulted in a reduced thermal threshold
and profound potentiation of heat-activated currents
in isolated small diameter neurons, and thermal hyperalgesia
in mice. SCF induced thermal hyperalgesia required the
TRP-family cation channel TRPV1. In addition, lack of c-Kit
signaling during development resulted in hypersensitivity of
discrete mechanoreceptive neuronal subtypes to mechanical
stimulation. Thus c-Kit, can be now be grouped into a small
family of receptor tyrosine kinases, including c-Ret and
TrkA, that control the transduction properties of distinct
types of sensory neuron to thermal and mechanical stimuli.
Roles of the Teashirt genes in neural circuits
Elena Rocca, Carola Griffel
We initially identified the Teashirt genes, encoding zinc
homeodomain transcription factors, together with c-Kit, in
a screen of gene expression in the substantia gelatinosa, an
area of particular importance for the reception of pain stimuli.
We have since generated knock-out mice for Tshz1
andTshz2 and conditional alleles for Tshz1 and Tshz3.
Analyses of spinal cord phenotypes in Tshz1 mutants indicated
redundancy in gene function with other Tshz genes
expressed in overlapping neuronal populations. We have
recently identified, however, a function of Tshz1 in the
olfactory bulb. The early development of the olfactory bulb
is still poorly understood, and many efforts have instead
been focussed on molecular analysis of the neurogenesis
that occurs in this structure throughout adult life. Our analyses
at present indicate that Tshz1 controls the development
of an early emigrating population of granule cell
interneurons that occupy the outer layer of the granule cell
layer in the maturing olfactory bulb. Analyses of cell proliferation
indicate that these cells are generated in the rostral
telencephalon already at E11.5-E12.5, and emigrate soon
after into the developing olfactory bulb. One short-term aim
is to determine the role of Tshz1 in the specification, proliferation
and/or migration of this early emigrating neuronal
population in embryonic development. Preliminary studies
indicate that mutant cells clump together and fail to distribute
radially within the olfactory bulb, a phenotype associated
with changes in Semaphorin signalling (identified by
microarray analysis). Interestingly, Tshz1 remains expressed
in the subventricular zone of the adult brain, the site
where continuous adult neurogenesis occurs to generate
interneurons destined to migrate into the olfactory bulb. In
the longer term, therefore, we will extend the analyses of
Tshz1 function to postnatal and adult neurogenesis, using
the conditional allele to circumvent the embryonic lethality
that occurs in the classical loss-of-function mutants.
Selected Publications
Milenkovic, N, Frahm, C, Gassmann, M, Griffel, C, Erdmann, B,
Birchmeier, C, Lewin, GR, Garratt, AN. (2007). Nociceptive
tuning by Stem Cell Factor/c-Kit signaling. Neuron, in press.
Grego-Bessa, J, Luna-Zurita, L, del Monte, G, Bolós, V, Melgar,
P, Arandilla, A, Garratt, AN, Zang, H, Mukouyama, Y, Chen, H,
Shou, W, Ballestar, E, Esteller, M, Rojas, A, Pérez-Pomares, de la
Pompa, JL. (2007). Notch signalling is essential for cardiac ventricular
chamber development. Developmental Cell 12: 415-429.
Willem, M, Garratt, AN*, Novak, B, Citron, M, Kaufmann, S,
Rittger, A, Saftig, P, De Strooper, B, Birchmeier, C, Haass, C.*
(2006). Control of peripheral nerve myelination by the (-secretase
BACE1. Science 314: 664-666 (*corresponding authors).
Garratt, AN. (2006). “To erb-B or not to erb-B...” Neuregulin-
1/ErbB signaling in heart development and function. J. Mol.
Cell. Cardiol. 41: 215-218.
López-Bendito, G, Cautinat, A, Sánchez, JA, Bielle, F, Flames, N,
Garratt, AN, Tagmale, D, Role, LW, Charnay, P, Marín, O, Garel,
S. (2006). Tangential migration controls axon guidance: a role
for Neuregulin-1 in thalamocortical axon navigation. Cell 125:
127-142.
158 Function and Dysfunction of the Nervous System