Expression Pattern and Genetics 
of Drosophila Synaptotagmin, a Synaptic 
Vesicle-Specific Protein 
The laboratory has recently embarked on a molec- 
ular and genetic analysis of Drosophila synaptotag- 
min {syt) , in collaboration with Dr. Mark Perin of 
the Division of Neuroscience, Baylor College of 
Medicine. SYT is a synaptic vesicle-specific mem- 
brane protein that has been suggested to play a key 
role in synaptic vesicle docking and fusion. In situ 
hybridizations shov^ that syt message is present in 
the cell bodies of many central nervous system 
(CNS) and all PNS neurons during neurite out- 
growth, synapse formation, and in fully developed 
embryos. Immunocytochemical staining of embryos 
with antibodies to SYT show that it is only tran- 
siently localized to the cell body of the neurons and 
that most of it is transported rapidly along the axons 
during axonogenesis. In the CNS, SYT is mostly lo- 
calized to two broad longitudinal tracts on the dor- 
sal side of the ventral nerve cord and the brain and at 
the neuromuscular junctions in the periphery. 
These results, when compared with the data ob- 
tained from vertebrates, suggest that the molecular 
mechanisms governing the localization of the syn- 
aptic vesicle before and after synapse formation as 
well as the function of SYT may be conserved from 
invertebrate to vertebrate species. 
Genetic analyses have allowed the mapping of the 
syt gene to cytological interval 23A4-23B2, which 
spans ~100 kb. Six homozygous lethal mutations 
that possibly fall into two complementation groups 
have been isolated and localized to this interval. 
Some allelic combinations of one of the comple- 
mentation groups cause embryonic lethality, and 
these embryos show reduced muscle contractions. 
These and other preliminary data suggest that the 
mutations affect syt. It is hoped that they will allow 
syfs function in vivo to be dissected. (This research 
is supported by the National Institutes of Health.) 
Dr. Bellen is also Assistant Professor in the Insti- 
tute for Molecular Genetics, the Division of Neuro- 
science, the Division of Developmental Biology, 
and the Department of Cell Biology at Baylor Col- 
lege of Medicine. 
Articles 
Bellen, H.J., D'Evelyn, D., Harvey, M., and El- 
ledge, S.J. 1992. Isolation of temperature-sensi- 
tive diphtheria toxins in yeast and their effects on 
Drosophila cells. Development 1 14:787-796. 
Bellen, H.J., Vaessin, H., Bier, E., Kolodkin, A., 
D'Evelyn, D., Kooyer, S., and Jan, Y.-N. 1992. 
The Drosophila couch potato gene: an essential 
gene required for normal adult behavior. Genet- 
ics 151:565-575. 
Whitehouse-Hills, S., Bellen, H.J., and Kiger, J.A., 
Jr. 1992. Embryonic cAMP and developmental 
potential in Drosophila melanogaster. Wil 
Roux's Arch Dev Biol 201:257-264. 
HEMATOLYMPHOID PRECURSOR DEVELOPMENT 
John W. Belmont, M.D., Ph.D., Assistant Investigator 
The production of mature blood cells depends on 
a tightly controlled developmental hierarchy of 
stem cells and committed progenitors. Dr. Bel- 
mont's laboratory is investigating the control of 
growth and differentiation of myeloerythroid and 
lymphoid precursor cells. The objective is to con- 
tribute to the understanding of the basic biology of 
these cells and to apply that information to the 
problems of immune deficiency diseases and human 
gene therapy. 
Hematopoietic Stem Cells 
A major goal is to be able to propagate stem cells 
in culture, since this would facilitate molecular 
analysis and have many medical applications. In 
order to clarify the role of the stromal cell interac- 
tions in the growth of stem cells in culture. Dr. Bel- 
mont's laboratory developed a novel strategy called 
mixed vector infection. A family of sister vectors 
was constructed by subcloning small random geno- 
mic DNAs into a weo-containing base vector (pN2). 
Each vector is easily distinguishable by polymerase 
chain reaction (PCR) . The vectors were produced at 
high titer and then used in marrow transduction ex- 
periments. Clones of cells should have a character- 
istic pattern of vector integration. This system was 
used to examine growth in short-term culture of 
marrow-repopulating activity cells (MRA, cells that 
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