Volume 17, Number 18,
Issue of September 15, 1997
pp. 6974-6987
Copyright ©1997 Society for Neuroscience
Selective Expression of Insulin-Like Growth Factor II in the
Songbird Brain
Received Feb. 25, 1997; revised June 5, 1997; accepted July 1, 1997.
Martin Holzenberger2,
Erich D. Jarvis1,
Christopher Chong1,
Matthew Grossman1,
Fernando Nottebohm1, and
Constance Scharff1
1 The Rockefeller University, New York, New York 10021, and 2 Institut d'Embryologie Cellulaire et
Moléculaire, Centre National de la Recherche Scientifique and
Collège de France, F-94736 Nogent-sur-Marne Cédex,
Nogent-sur-Marne, France
Neuronal replacement occurs in the forebrain of juvenile and adult
songbirds. To address the molecular processes that govern this
replacement, we cloned the zebra finch insulin-like growth factor II
(IGF-II) cDNA, a factor known to regulate neuronal development and
survival in other systems, and examined its expression pattern by
in situ hybridization and immunocytochemistry in
juvenile and adult songbird brains. The highest levels of IGF-II mRNA
expression occurred in three nuclei of the song system: in the high
vocal center (HVC), in the medial magnocellular nucleus of the
neostriatum (mMAN), which projects to HVC, and to a lesser extent in
the robust nucleus of the archistriatum (RA), which receives
projections from HVC. IGF-II mRNA expression was developmentally
regulated in zebra finches. In canary HVC, monthly changes in IGF-II
mRNA expression covaried with previously reported monthly differences in neuron incorporation. Combining retrograde tracers with in situ hybridization and immunocytochemistry, we determined that the
HVC neurons that project to area X synthesize the IGF-II mRNA, whereas
the adjacent RA-projecting neurons accumulate the IGF-II peptide. Our
findings raise the possibility that within HVC IGF-II acts as a
paracrine signal between nonreplaceable area X-projecting neurons and
replaceable RA-projecting neurons, a mode of action that is compatible
with the involvement of IGF-II with the replacement of neurons.
Additional roles for IGF-II expression in songbird brain are likely,
because expression also occurs in some brain areas outside the song
system, among them the cerebellar Purkinje cells in which neurogenesis
is not known to occur.
Key words:
adult neurogenesis;
Golgi;
development;
neurotrophins;
growth factors