Genetic Control of Morphogenesis 
Thomas C. Kaufman, Ph.D. — Investigator 
Dr. Kaufman is also Professor of Genetics in the Department of Biology at Indiana University and Adjunct 
Professor of Medical Genetics in the Department of Medical Genetics at Indiana University Medical Center. 
He received his M.A. and Ph.D. degrees from the University of Texas, Austin, and did his postdoctoral re- 
search at the University of British Columbia in Vancouver, B.C. He is currently Secretary of the Genetics 
Society of America. 
OUR continuing goal is to understand how the 
essentially one-dimensional linear informa- 
tion encoded in the DNA molecule is elaborated 
into a three-dimensional organism during the pro- 
cess of development. As a model system in this 
analysis, we are using the fruit fly Drosophila 
melanogaster and are concentrating on a group 
of adjacent genes in a small region of one chro- 
mosome arm. Mutations in these homeotic genes 
transform one organ of the fly embryo, larva, or 
adult into a homologous structure. For example, 
mutations in the Antennapedia gene transform 
the antenna of the adult fly into a leg, while muta- 
tions in the proboscipedia gene transform the 
mouthparts into legs. 
A combined genetic and developmental analy- 
sis of this region of the Drosophila chromosome 
has revealed the presence of five such genes that 
are collectively referred to as the Antennapedia 
gene complex (ANT-C) . These five genes collec- 
tively specify the proper identity of the anterior 
end of the fruit fly and can be viewed as develop- 
mental switches that make either/or decisions in 
cell fate at specific times and places in the em- 
bryo and larva. 
Recombinant DNA technology has allowed the 
cloning of the genes and has revealed the nature 
of their protein products. All of the homeotic 
genes contain a specific DNA sequence that en- 
codes a common protein motif called the homeo- 
box. It has been shown that this motif acts as a 
DNA-binding domain and that these homeotic 
proteins are associated with the chromosomes in 
the nuclei of the developing fly. Therefore we 
now know that these homeotic genes act as devel- 
opmental switches because their protein prod- 
ucts serve to regulate directly the expression of 
other genes. What we do not fully understand is 
how these homeotic genes are so elegantly or- 
chestrated in their proper spatiotemporal pat- 
terns and what is the nature of the battery of genes 
that are in turn regulated by the protein products 
of the five members of the ANT-C. Our current 
research is focused on these two questions. 
We are using three of the five genes in the com- 
plex — labial (Jab) , proboscipedia (pb) , and Sex 
combs reduced (5cr) — in our attempts to under- 
stand spatiotemporal patterning. These were 
chosen because of the unique properties 
each displayed during our initial characteriza- 
tion of their respective roles in Drosophila 
development. 
The labial Gene 
Using a minigene construct and P-element-me- 
diated transformation, we have been able to ame- 
liorate completely the embryonic defects asso- 
ciated with lab deficiency; however, adult 
transgenic animals show severe deformities, with 
thoracic structures replacing portions of the head 
capsule. We have now shown that this defect is 
caused not by a failure of lab activity in the devel- 
oping adult head but by the ectopic expression of 
the minigene in the head anlagen, which is also 
associated with a failure to express the Deformed 
(Dfd) and Scr loci in their normal pattern in this 
same tissue. Thus it appears that lab can act as a 
transregulator of these other homeotic members 
of the ANT-C. This is in marked contrast to our 
observation that cross-regulatory interactions do 
not take place among any of the ANT-C homeotic 
loci in the embryo. It would appear therefore that 
the regulatory hierarchy in the embryo and adult 
stages is difi'erent. 
The fact that the minigene shows ectopic ex- 
pression only in a lab~ background points up an- 
other regulatory phenomenon. Since the resident 
lab gene is able to prevent ectopic expression, 
the native protein appears to be able to influence 
the expression of the minigene negatively: i.e., 
lab shows autogenous negative regulation. The 
product of the minigene, however, does not per- 
form this function. In the construction of the 
minigene we used a cDNA fragment that did not 
include a minor alternate splice form. This alter- 
nate RNA product would produce a protein prod- 
uct that is six amino acids longer than the single 
protein encoded by the minigene. The resident 
gene can, of course, make both proteins. These 
observations lead to the exciting possibility that 
the longer protein product is responsible for the 
negative regulation and that the short form is inca- 
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