the transcriptional start site. When the distribution 
of transgene transcripts in liver was examined using 
in situ hybridization, it was shown that they were 
nonuniform in the liver acinus. Hepatocytes 
surrounding the central veins expressed high levels 
of minigene transcripts, while hepatocytes in the 
intermediate and periportal areas contained few if 
any transcripts. These results indicate that the com- 
plete repression of the AFP gene is a complex pro- 
cess, in that repression in the pericentral hepato- 
cytes is solely dependent upon the presence of the 
— 250- to — 838-bp negative-regulatory domain, 
while the intermediate zone and periportal hepato- 
cytes require an additional element(s). 
Genetic and Physical Mapping 
of the Fused Gene 
The Fused {Fu} locus on mouse chromosome 1 7 
was originally identified by spontaneous dominant 
mutations that result in kinky-tailed mice. Fu homo- 
zygous mice die at midgestation, as the result of 
overgrowth of neuroectoderm. In preparation for 
cloning of Fu, the laboratory completed the analysis 
of a 1 ,000-animal backcross between Fu"' mice and 
Mus spretus, designed to localize Fu within 0.1 cM, 
or ~ 100-200 kb of DNA. The cross was typed for 
Fu, tufted (a recessive phenotypic marker that maps 
near Fu^, and four tightly linked DNA markers. 
This cross identified the closest linked marker as 
Hba-ps4, a pseudogene of a-globin. Only a single 
recombination event had occurred between Fu and 
Hba-ps4 in the 1,000 animals, indicating that they 
should be within 100-200 kb of each other. Seven 
overlapping YACs encompassing ~600 kb of DNA 
have been isolated using Hba-ps4 as an entry point. 
When the farthest ends of this contig were mapped 
in the backcross, no recombination between them 
was observed. Thus the region around Fu has a low 
frequency of recombination. 
Genetic and Phenotypic Analysis 
of piebald 
The spotting of piebald is a result of a defect in 
the development of a subset of the neural crest cells 
that gives rise to pigment-producing melanocytes. 
These mice also develop megacolon, the result of 
the failure of another neural crest derivative, enteric 
ganglia, to develop appropriately. There are many 
alleles of piebald, thanks to its inclusion as a scor- 
able mutation in a large-scale mutagenesis program, 
conducted over many years by Drs. William and 
Leane Russell at the Oak Ridge National Laboratory. 
By using cellular markers specific to the neural crest 
cells leading to melanocytes and/or enteric ganglia, 
the laboratory established that the piebald defect is 
apparent as early as day 13.5 of embryogenesis, 
when the neural crest cells are migrating away from 
the neural tube. 
A 500-animal backcross between piebald mice 
and Mus castaneus has been generated and ana- 
lyzed for DNA markers on chromosome 1 4 . One of 
these markers has been mapped to within 0.5 cM of 
piebald, a distance feasible for chromosome walk- 
ing. The markers have been used to demonstrate the 
high degree of heterogeneity in the sizes of the dele- 
tions in 13 alleles of piebald obtained from Oak 
Ridge, most of which are embryonic lethals when 
homozygous. 
Dr. Tilghman is also Howard A. Prior Professor 
of the Life Sciences in the Molecular Biology De- 
partment at Princeton University and Adjunct 
Professor of Biochemistry at the University of Med- 
icine and Dentistry of New fersey, Robert Wood 
Johnson Medical School. 
Books and Chapters of Books 
Davies, K.E., and Tilghman, S.M., editors. 1991. 
Genome Analysis: Gene Fxpression and Its Con- 
trol. Cold Spring Harbor, NY: Cold Spring Harbor, 
vol II. 
Davies, K.E., and Tilghman, S.M., editors. 1991. 
Genome Analysis: Genes and Phenotypes. Cold 
Spring Harbor, NY: Cold Spring Harbor, vol 111. 
Articles 
Bartolomei, M.S., and Tilghman, S.M. 1992. Paren- 
tal imprinting of mouse chromosome 7. Semin 
Dev Biol 5:107-117. 
Rossi, J.M., Burke, D.T., Leung, J.C.M., Koos, D.S., 
Chen, H., and Tilghman, S.M. 1992. Genomic 
analysis using a yeast artificial chromosome li- 
brary with mouse DNA inserts. Proc Natl Acad Sci 
USA 89:2456-2460. 
Vacher, J., Camper, S.A., Krumlauf, R., Compton, 
R.S., and Tilghman, S.M. 1992. ra/regulates the 
postnatal repression of the a-fetoprotein gene at 
the posttranscriptional level. Mol Cell Biol 
12:856-864. 
GENETICS 275 
