Molecular Genetics of Mammalian 
Glycosyltransferases 
\ ^4 
John B. Lowe, M.D. — Assistant Investigator 
Dr. Lowe is also Assistant Professor of Pathology at the University of Michigan Medical School. He received 
his bachelor's degree in mathematics from the University of Wyoming and his M.D. degree from the Uni- 
versity of Utah College of Medicine. He was trained in clinical pathology and molecular genetics at Wash- 
ington University School of Medicine in St. Louis. He was later Assistant Professor in the Departments of 
Pathology and Medicine at Washington University and also served as Assistant Medical Director of the 
Barnes Hospital blood bank, St. Louis, before moving to Michigan. 
THE primary long-range goal of our research is 
to understand the functions of molecules 
called oligosaccharides that are found on the sur- 
face of mammalian cells and to explain how the 
cells regulate expression of these molecules. Oli- 
gosaccharides consist of many different sugar 
structures linked together in complex linear and 
branching arrays. Quantitative and structural 
changes in such molecules have been show^n to 
correlate with morphologic changes that occur 
during the embryonic development of animals 
and in association with neoplastic transforma- 
tion. These and other observations suggest that 
cell surface oligosaccharides may function as in- 
formation bearers in mediating interactions be- 
tween cells during the developmental process. 
Mammalian cells, in constructing these mole- 
cules, use special proteins called glycosyltrans- 
ferase enzymes. With few exceptions, a unique 
glycosyltransferase is responsible for the synthe- 
sis of each linkage between the sugar molecules 
in an oligosaccharide. The enormous number of 
diflf^erent oligosaccharides dictates that many dif- 
ferent glycosyltransferases will enter the con- 
struction of the complex cell surface carbohy- 
drates on any particular cell or tissue. 
In many instances, changes in cell surface car- 
bohydrate structure observed during differentia- 
tion or in association with malignant transforma- 
tion have been shown to correlate with changes 
in the glycosyltransferase repertoire. The mecha- 
nisms by which cells coordinate and regulate the 
expression of these enzymes, and thus the ex- 
pression of oligosaccharide structures at the cell 
surface, are unknown. During the past few years, 
the main focus of our work has been in establish- 
ing systems that will allow molecular analysis of 
the mammalian genes responsible for glycosyl- 
transferase synthesis. 
The human ABO, H, and Lewis blood group an- 
tigens are actually cell surface oligosaccharides. 
The determinant genes encode particular glyco- 
syltransferases that are able to construct the 
"blood group" molecules. These glycosyltrans- 
ferases provide convenient genetic and biochemi- 
cal models for studying the processes that allow 
mammalian cells to regulate cell surface oligosac- 
charide expression. 
The blood group antigens are not restricted in 
their expression to blood cells. They are found on 
a number of other tissues in the body, suggesting 
that tissue-specific mechanisms regulate their ex- 
pression. Moreover, their expression changes 
during human embryonic development and is of- 
ten altered in malignancy. 
Our initial efforts have focused on developing 
systems to isolate glycosyltransferase genes with- 
out the benefit of purified enzyme protein. In 
one instance, we isolated the gene for human H 
blood group a(l,2)fucosyltransferase, using a 
scheme in which the gene was first transferred 
into a cultured mouse cell line by a process 
called transfection. We were then able to use mo- 
lecular cloning procedures to retrieve the human 
gene from the mouse genome. 
We have also used a similar technical approach 
to isolate other glycosyltransferase genes. This 
scheme involves transfer of cloned segments of 
human genes back and forth between animal cells 
and the bacterial host cells used for molecular 
cloning purposes. With this approach an a (1,3/ 
1 ,4)fucosyl transferase gene, for example, was 
isolated that represents the human Lewis blood 
group locus. We have recently used the H and 
Lewis gene segments and cross-hybridization pro- 
cedures to isolate still other glycosyltransferase 
genes with related or unique structural and func- 
tional properties. 
The cloned gene segments in each case repre- 
sent tools for investigating the function and regu- 
lation of cell surface oligosaccharides. For exam- 
ple, we recently used these gene segments to 
identify specific cell surface oligosaccharide mol- 
ecules that play pivotal functional roles in the 
inflammatory process. One of the primary events 
in inflammatory conditions involves a process 
whereby circulating white cells leave the interior 
of blood vessels and become localized in inflam- 
matory foci outside the vascular system. This pro- 
cess begins when the endothelial cells lining the 
blood vessels become "activated" by substances 
that accompany an incipient inflammatory condi- 
tion. Circulating white cells known as neutro- 
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