some, by virtue of its large si2e, can be separated 
easily with a fluorescence-activated chromosome 
sorter. In collaboration v^ith Scott Cram and Kevin 
Albright at the Los Alamos National Laboratory, Dr. 
Friedman's laboratory has constructed a genomic li- 
brary from the flov^^-sorted 4,6 chromosome and is 
currently mapping phage clones from this resource. 
In addition, v^^ith the help of Dr. Steve Brov^^n in En- 
gland, Dr. Friedman's group is using microdissec- 
tion and microcloning techniques to make libraries 
from the distal region of mouse chromosome 4 
(where db is located) and the proximal region of 
mouse 6 (where ob is located). The use of chromo- 
some-specific libraries of these probes for "satura- 
tion" mapping of these chromosomes is a first step 
toward the cloning of the ob and db genes. The 
presence of markers tightly linked to ob {met and 
cpa) and db (interferon-a and c-jun) should make 
it possible to generate physical maps (long-range 
restriction maps) of these regions of the mouse ge- 
nome using pulsed-field gel electrophoresis. These 
experiments are under way and should accelerate 
efforts to obtain other clones that are tightly linked 
to ob and db. 
II. Cholecystokinin Regulation and Function. 
The hormone CCK was originally found in the 
small intestine by virtue of its ability to stimulate 
gallbladder contraction and pancreatic secretion in 
response to feeding. High levels of CCK were re- 
cently found in neurons of the mammalian brain, 
where it functions as a neurotransmitter. In the 
brain this neuropeptide is found in subsets of neu- 
rons in several regions that differ in their 
morphologic, functional, and biochemical charac- 
teristics. 
Dr. Friedman's objective is to elucidate the mo- 
lecular mechanisms controlling the expression of 
the CCK gene in each of the cell types that express 
CCK RNA. A full understanding of the regulation of 
this gene in each of the expressing cell types would 
yield insight into the genetic strategies employed in 
instances where the same gene is expressed in dif- 
ferent cell types. Dr. Friedman and his colleagues 
are also employing a variety of techniques in molec- 
ular biology to explore the function(s) of this 
hormone. 
Previously the laboratory cloned and sequenced 
the single-copy mouse CCK gene. Before the DNA 
sequences involved in the transcriptional control of 
the CCK gene could be defined, it was necessary to 
identify cultured cell lines that express this gene. 
Two separate pediatric tumor/cell lines that express 
the CCK gene were initially identified. Both tumors 
were derived from neuroepitheliomas, which are 
primitive nerve tumors that usually develop in the 
chest wall. Dr. Maria Vitale has used these cell lines 
to demonstrate that cell-specific expression of the 
CCK gene in cultured neuroepithelioma cells and 
cell-specific repression in cultured cells that do not 
synthesize CCK mRNA require the presence of DNA 
sequences between -6.5 and -13.5 kb. A more pre- 
cise localization of these DNA sequences is cur- 
rently being determined by deletion analysis. 
After observing that CCK RNA is present in two 
neuroepitheliomas. Dr. Friedman screened eight 
additional tumor cell lines of this type and discov- 
ered that all neuroepitheliomas synthesize this 
mRNA. Eight out of eight cell lines derived from a 
pediatric bone tumor thought to resemble neu- 
roepitheliomas, Ewing's sarcoma of bone, also ex- 
press CCK mRNA. Subsets of other pediatric tu- 
mors, including rhabdomyosarcoma, a malignant 
muscle tumor, also appear to express the CCK 
gene. Since CCK is a neural marker, these data sug- 
gest that there may be a class of pediatric nerve cell 
tumors that express this hormone and that synthe- 
sis of this peptide may be of diagnostic value in pe- 
diatric solid tumors. The possibility that CCK-pro- 
ducing tumors have a different clinical course and 
require different therapy than tumors that do not 
synthesize this hormone needs to be considered. 
Most of these tumors do not, however, process the 
CCK prohormone and hence do not synthesize im- 
munoreactive CCK. They do secrete the CCK pro- 
tein precursor, which can be detected by use of a 
novel radioimmunoassay to the carboxyl terminus 
of the CCK precursor that was developed by Dr. 
Bruce Schneider and Dr. Friedman. In preliminary 
experiments with this radioimmunoassay, it appears 
that the blood levels of the CCK precursor are ele- 
vated in patients with the aforementioned tumors. 
These observations also suggest that ectopic CCK 
production could in some cases have pathophysio- 
logic effects in humans. 
To describe the implications of ectopic CCK 
production and to consider the role of CCK in the 
control of feeding behavior. Dr. Friedman has, in 
collaboration with Drs. Richard Palmiter (HHMI, 
University of Washington) and Ralph Brinster 
(University of Pennsylvania), artificially expressed 
high levels of this hormone in blood by fusing 
the metallothionein (MT) promoter to the CCK 
coding sequence and introducing the MT-CCK 
transgene into transgenic mice. Transgenic mice 
Continued 
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