ing. The majority of the interval is now cloned, and a 
search for candidate genes has begun. The identifi- 
cation of the responsible gene, which is estimated to 
be present in approximately 1 in 200 women, 
would allow widespread screening in order to iden- 
tify women at high risk. Given that intensive screen- 
ing is often likely to be lifesaving, such a test could 
find wide application and be a major step forward in 
preventive medicine. 
Huntington's Disease 
In collaboration with six other laboratories in the 
United States and the United Kingdom, the Collins 
laboratory is pursuing the gene for Huntington's dis- 
ease, which has been narrowed down to an interval 
of ~2.3 million base pairs on the shon arm of chro- 
mosome 4 . A complete set of YACs that cover this 
interval has been constructed, and those cloned 
fragments are now being used as the substrate for 
identifying candidate genes. 
This has involved the development of new tech- 
nologies capable of scanning such large intervals for 
coding regions. One such technique in which 
cDNAs are trapped against genomic DNA using a 
magnetic capture method appears to have broad 
promise for the rapid identification of a large num- 
ber of genes in one experiment and has yielded sev- 
eral attractive candidates. It is estimated that approx- 
imately 100 genes will be contained within this 
large interval, and the proof of the correctness of 
any one candidate will depend upon the identifica- 
tion of a single mutation, which may be as subtle as a 
single nucleotide change. A large-scale sequencing 
efi'ort is also being mounted in order to speed this 
activity. 
This project is supported in part by a grant from 
the Hereditary Disease Foundation. 
Cystic Fibrosis 
The cystic fibrosis gene, identified by the Collins 
laboratory in collaboration with investigators at the 
Hospital for Sick Children in Toronto in 1989, con- 
tinues to produce a series of interesting observations 
that are further clarifying the basic molecular biol- 
ogy of the disease and beginning to suggest new 
modes of therapy. In collaboration with Dr. David 
Dawson, the Collins laboratory has been successful 
in expressing wild-type CFTR (cystic fibrosis trans- 
membrane regulator) and various naturally occur- 
ring cystic fibrosis mutants in Xenopus oocytes 
(frog eggs) . The normal CFTR RNA produces a dra- 
matic chloride flux after cyclic AMP activation, pro- 
viding an excellent model for looking at structure/ 
function characteristics of CFTR. 
Surprisingly, the common AF508 CFTR mutation, 
which had previously been assumed to inactivate 
the gene completely, turns out to have partial activ- 
ity in this assay. Using drugs that maximally elevate 
cyclic AMP, the AF508 protein can be induced to 
approximately wild-type levels of current. Although 
much remains to be determined regarding the basis 
of this effect, the observation suggests the possibil- 
ity of a new form of drug therapy that could activate 
the mutant in the airways of alfected individuals. 
Extensive investigations are also under way to iden- 
tify the regulation of gene expression of CFTR and to 
understand the mechanism by which the protein is 
activated during phosphorylation. 
This project is supported in part by a grant from 
the National Institutes of Health. 
Neurofibromatosis 
The gene for type 1 neurofibromatosis (NFl) was 
identified in the Collins laboratory in 1 990, and pro- 
gress continues in defining the molecular biology of 
this common dominant disease. A variety of antisera, 
raised against synthetic peptides and fusion proteins 
for the NFl gene product, have been used to identify 
the protein by Western blotting, immunoprecipita- 
tion, and immunofluorescence. The protein is ex- 
pressed in all tissues examined, but has highest lev- 
els in the central nervous system. It has homology to 
the GTPase-activating protein (GAP), which inter- 
acts with the oncogene product ras, and this rela- 
tionship is being dissected by carrying out mutagen- 
esis experiments on neurofibromin, the protein 
product of the NFl gene. Immunofluorescence ex- 
periments have demonstrated the unexpected find- 
ing that the NFl protein appears to be associated 
with microtubules. This connection between ras- 
mediated signal transduction and the cytoskeleton 
represents a totally unexpected finding, and one 
that may be fundamental to the regulation of cell 
division. 
In addition, the full-length cDNA for NF 1 has been 
cloned and the entire sequence determined, and the 
genomic sequence has been obtained in a series of 
YACs that cover the entire gene. 
A recent surprising observation is the discovery of 
frequent mutations in this gene in patients with spo- 
radic malignant melanoma, the most common form 
of fatal skin cancer. This further broadens the role of 
NFl in human disease. 
This project was supported in part by a grant from 
the National Institutes of Health. 
Dr. Collins is also Professor of Internal Medi- 
cine and Human Genetics at the University of 
Michigan Medical School and a member of the Di- 
vision of Molecular Medicine and Genetics. 
GENETICS 173 
