Control of Cell Fate During Vertebrate 
Neuronal Development 
David J. Anderson, Ph.D. — Assistant Investigator 
Dr. Anderson is also Assistant Professor of Biology at the California Institute of Technology and Adjunct 
Assistant Professor of Anatomy and Cell Biology at the University of Southern California School of Medi- 
cine. He received his A.B. degree in biochemical sciences from Harvard College and a Ph.D. degree in cell 
biology from the Rockefeller University for work with Gunter Blobel. He then did postdoctoral research in 
molecular neurobiology with Richard Axel at Columbia University. He counts among his honors a Searle 
Scholars Award and an NSF Presidential Young Investigator Award. 
WE are interested in liow different types of 
nerve cells are generated during the devel- 
opment of the vertebrate nervous system. We 
have chosen to work on the peripheral auto- 
nomic nervous system, which is simpler and 
more accessible than the brain. Our studies have 
focused on the development of two specific cell 
types: the sympathetic neurons that lie in a chain 
of ganglia along the spinal cord, and the chromaf- 
fin cells of the adrenal medulla. These two cells 
are closely related, yet distinct in major respects. 
The former are true neurons, with long branching 
axons and dendrites that send and receive electri- 
cal signals. The latter are small, round secretory 
cells that release epinephrine (adrenaline) into 
the bloodstream during fright or excitement. 
Studies in a number of laboratories, including 
our own, have established that these two cell 
types derive from a common progenitor cell. This 
cell arises on top of the neural tube (the develop- 
ing spinal cord), as part of a transient structure 
called the neural crest. Like parachutists, the 
neural crest cells peel off the neural tube in a 
wave and migrate downward through the em- 
bryo. Some of them arrest their migration in a 
chain of small clumps along a blood vessel, 
where they eventually become sympathetic neu- 
rons. Others continue their migration downward 
to invade the developing adrenal gland, where 
they become chromaffin cells. 
Using a fluorescence-activated cell sorter and 
specific monoclonal antibodies to tag the cells, 
we have succeeded in isolating chromaffin cell 
precursors from the fetal adrenal gland of the rat. 
By manipulating the culture environment of the 
cells, we have shown that these precursors have 
two possible developmental fates: if glucocorti- 
coid hormones are added to the growth medium, 
mimicking the environment of the adrenal gland, 
the precursors develop into chromaffin cells. If, 
on the other hand, fibroblast growth factor (FGF) 
and nerve growth factor (NGF) are added to the 
medium, the precursors develop into sympa- 
thetic neurons. This indicates that the fate of 
these cells is determined in large part by signals 
in the environments to which they migrate. How- 
ever, these precursors seem to have lost the abil- 
ity to give rise to some other derivatives of the 
neural crest, such as glial cells. Therefore, while 
these precursor cells have a choice of fate, it is a 
restricted one. 
Immortalization of the Chromaffin-Neuron 
Precursor Cell 
The precursor cell is endowed with a limited 
repertoire of potential developmental fates. What 
genes and proteins determine the specific reper- 
toire of possible fates? What genes and proteins 
select a particular fate for actual expression? 
These are the major questions we are pursuing in 
an effort to understand the molecular biology of 
this developmental system. 
One problem in studying the chromaffin- 
neuron precursor cell at the molecular level is 
the small number of cells that can be isolated 
from rat fetuses. To circumvent this problem, we 
have applied recently developed techniques to 
immortalize the cells. Using a defective retrovi- 
rus as a "disposable molecular syringe," we have 
injected the cells with a gene, y-myc, that allows 
them to divide forever in the culture dish. In this 
way we can generate an endless supply of cells 
that can be used for experiments at any time, 
without the need to perform long hours of dissec- 
tion. Fortunately, these immortalized precursor 
cell lines still appear capable of undergoing dif- 
ferentiation into sympathetic neurons when ex- 
posed to FGF and NGF. 
Neural Development in Mammals and 
Drosophila Uses Similar Regulatory 
Molecules 
We have used the chromaffin-neuron precursor 
cell lines to isolate new genes that may be candi- 
dates for controlling the development of these 
cells. This approach involves first guessing that a 
particular gene, or class of genes, may be ex- 
pressed in the precursor cell and then using the 
tools of molecular biology to extract the gene of 
interest. What guidelines can one use to make 
educated guesses about developmental control 
genes? One suggestion came from studies, by 
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