and cell bodies or axons and possibly terminals. 
Thus different potassium channels of similar bio- 
physical properties may be targeted to different sub- 
cellular compartments of a neuron and thereby be- 
come specialized with respect to their functional 
role. (The studies of potassium channels in the 
mammalian brain are supported by the National In- 
stitute of Mental Health.) 
Dr. Lily Jan is also Professor of Physiology and 
of Biochemistry and Biophysics at the University 
of California, San Francisco. 
Articles 
Baldwin, T.J., Tsaur, M.L., Lopez, G.A., Jan, Y.N., 
and Jan, L.Y. 1991. Characterization of a mam- 
malian cDNA for an inactivating voltage-sensitive 
channel. Neuron 7:47l-485- 
Boulianne, G.L., de la Concha, A., Campos-Ortega, 
J. A., Jan, L.Y., and Jan, Y.N. 1991 . The Drosoph- 
ila neurogenic gene neuralized encodes a novel 
protein and is expressed in precursors of larval 
and adult neurons. EMBO J 10:2975-2983. 
Isacoff, E.Y., Jan, Y.N., and Jan, L.Y. 1991. Puta- 
tive receptor for the cytoplasmic inactivation gate 
in the Shaker channel. Nature 353:86-90. 
Jan, L.Y., and Jan, Y.N. 1992. Structural elements 
involved in specific channel functions. Annu 
Rev Physiol 54:537-555. 
Jan, L.Y., and Jan, Y.N. 1992. Tracing the roots of 
ion channels. Ce// 69:715-718. 
Jan, Y.N., and Jan, L.Y. 1992. Neuronal specifica- 
tion. Curr Opin Genet Dev 2:608-613. 
Jongens, T.A., Hay, B., Jan, L.Y., and Jan, Y.N. 
1992. The germ cell-less gene product: a posteri- 
orly localized component necessary for germ cell 
development in Drosophila. Cell 70:569-584. 
Li, M., Jan, Y.N., and Jan, L.Y. 1992. Specification 
of subunit assembly by the hydrophilic amino- 
terminal domain of the Shaker potassium channel. 
Science 257:1225-1230. 
Rao, Y., Vaessin, H., Jan, L.Y., and Jan, Y.N. 1991. 
Neuroectoderm in Drosophila embryos is depen- 
dent on the mesoderm for positioning but not for 
formation. Genes Dev 5:1511 -\5S8. 
Sheng, M., Tsaur, M.L., Jan, Y.N., and Jan, L.Y. 
1992. Subcellular segregation of two A-type 
channel proteins in rat central neurons. Neuron 
9:271-284. 
Timpe, L.C., Isacoff, E., Kimmerly, W., Papa- 
zian, D., Jan, Y.N., and Jan, L.Y. 1991. Molecu- 
lar studies of voltage-gated potassium channels. 
Fidia Res Found Symp Ser 1:S>-\1 . 
Tsaur, M.L., Sheng, M., Lowenstein, D.H., Jan, 
Y.N., and Jan, L.Y. 1992. Differential expression 
of channel mRNAs in the rat brain and down- 
regulation in the hippocampus following sei- 
zures. Neuron 8:1055-1067. 
Vaessin, H , Grell, E., Wolff, E., Bier, E., Jan, L.Y., 
and Jan, Y.N. 1991. prospero is expressed in neu- 
ronal precursors and encodes a nuclear protein 
that is involved in the control of axonal out- 
growth in Drosophila. Cell 67:941-953. 
NEURAL DEVELOPMENT IN DROSOPHILA 
YuhNungJan, Ph.D., Investigator 
Dr. Jan and his colleagues are interested in the 
mechanisms of cell determination and differentia- 
tion during neural development. How do neurons 
arise from undifferentiated ectodermal cells? What 
gives the neurons their individual identities in terms 
of shape and function? How are neuronal pathways 
initially established? The long-term goal is to under- 
stand these processes at the molecular level. A ge- 
netic approach is being used; i.e., the studies begin 
with the isolation of Drosophila mutants that affect 
neurogenesis, neuronal type, or axonal pathway for- 
mation. Identification of the mutations can lead to the 
isolation of genes important in neural development. 
Studies by this group and others have identified a 
number of genes that specify cell fate in the embry- 
onic sensory nervous system of Drosophila. The 
genes appear to act at different steps progressively 
to restrict the cells to more and more determined 
fates, as outlined below. 
Early during embryogenesis, at the cellular blas- 
toderm stage, a group of genes called proneural 
genes determine where the nervous system de- 
velops. Proneural genes are expressed in clusters of 
cells and thereby endow those cells with the poten- 
tial to form neuronal precursors. As a neuronal pre- 
cursor forms, it inhibits neighboring cells from do- 
ing so. This lateral inhibition involves the action of 
neurogenic genes. The commitment of neuronal 
NEUROSCIENCE 411 
