B. numb. A simple external sensory organ precur- 
sor divides twice to give rise to four progeny cells: a 
neuron, a glia, a socket-formatting cell, and a hair- 
forming cell. Mutations affecting this cell lineage 
might be expected to alter neuronal number, numb 
is such a mutation. The phenotype of numb is the 
following: 1) The number of the sensory neurons is 
severely reduced, to —10% of normal. 2) All four 
progeny of a sensory organ precursor are present. 
Thus the loss of sensory neurons is not due to cell 
death. 3) The socket and hair are often duplicated 
in a sensory organ. The simplest interpretation of 
these observations is that numb affects the sensory 
organ lineage in such a way that the cells that nor- 
mally give rise to neuron and glia are transformed 
into cells that form socket and hair. This gene has 
recently been cloned by Dr. Tadashi Uemura in this 
laboratory. The sequences suggest that the gene 
product may contain a zinc finger. 
lY Mutations Affecting Axonal Pathways. 
A number of mutants were found to cause abnor- 
mality in neuronal pathways. Dr. Edward Giniger 
has started to analyze some of those mutants. 
V Additional Genes Involved in Neural 
Development. 
Several thousands of lines, each one with a single 
P insertion, have been generated. The P element 
used in this laboratory was constructed by Dr. 
PUBLICATIONS 
Ethan Bier and Kevin Lee and contains mini-white 
{w^), lacZ, and PUC sequences. 
The if ^ gene is used as a genetic marker to fol- 
low the insertion. It also contains a lacZ gene fused 
in frame with the transposase. Because the trans- 
posase has a weak promoter, the expression of lacZ 
depends on the site of insertion (presumably under 
the influence of a nearby promoter or enhancer el- 
ements). By doing an X-Gal reaction, one can ask 
whether there is an interesting pattern of expres- 
sion associated with the insertion. This has two 
useful applications. 1) Useful cell-type-dependent 
promoters can be isolated. 2) The P-galactosidase 
expression is dominant. Heterozygous transformant 
lines showing interesting patterns can be selected 
for further tests of possible phenotypes associated 
with the insertion in homozygotes. One can also at- 
tempt to delete the region by isolating mutants that 
have lost the w'^ gene (and probably the entire P 
element, perhaps with some flanking sequences) 
and testing for phenotype associated with the dele- 
tion. The PUC sequence containing the origin of 
replication and ampicillin resistance is used for 
speedy cloning via plasmid rescue. This mutant 
screening is designed to find mutants affecting vari- 
ous aspects of function and development of the 
nervous system. 
Dr. Yuh Nung Jan is also Professor of Physiology 
and Biochemistry at the University of California at 
San Francisco. 
Books and Chapters of Book 
Schwarz, T.L., Carretto, R., Papazian, D., Tempel, B., Timpe, L., Jan, YN. , and Jan, L.Y 1989. A family of potas- 
sium channels from the Shaker locus in Drosophila. In Molecular Biology of Neuroreceptors and Ion 
Channels (Maelicke, A., Ed.). New York: Springer-Verlag, pp 215-229. 
Articles 
Bodmer, R., Carretto, R., and Jan, YN. 1989. Neurogenesis of the peripheral nervous system in Drosophila 
embryos: DNA replication patterns and cell lineages. Neuron 3:21-32. 
Caudy, M. , Vaessin, H., Brand, M., Tuma, R. , Jan, L.Y , and Jan, YN. 1988. daughterless, 2l Drosophila gene es- 
sential for both neurogenesis and sex determination, has sequence similarities to myc and the achaete- 
scute complex. Cell 55:1061-1067. 
Dambly-Chaudiere, C, Ghysen, A., Jan, L.Y, and Jan, YN. 1988. The determination of sense organs in Dro- 
sophila: interaction of scute with daughterless. Roux'sArch Dev Biol 197:419-423. 
Hay, B., Jan, L.Y, and Jan, YN. 1988. A protein component of Drosophila polar granules is encoded by vasa 
and has extensive sequence similarity to ATP-dependent helicases. Cell 55:577-587. 
Jan, L.Y , and Jan, YN. 1989. Voltage-sensitive ion channels. Cell 56:13-25. 
Continued 
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