INTERNATIONAL RESEARCH SCHOLARS 
In recognition of the contributions of scientists 
outside of the United States to advances in biomedi- 
cal science, the Institute initiated the International 
Research Scholars Program in 1991- This is a small 
and experimental effort that provides five-year 
grants to support the research of promising scien- 
tists working in areas of fundamental biomedical re- 
search related to the Institute's ongoing medical 
research programs. 
Canada and Mexico were chosen as the eligible 
countries for awards in 1991. From those invited to 
compete, 24 were designated International Re- 
search Scholars (14 in Canada, 10 in Mexico), and 
grants were made to their institutions for support of 
their research. Grants also were awarded to the Mex- 
ican Academia de la Investigacion Cientifica and to 
the United States National Academy of Sciences for 
joint activities over four years to promote the ex- 
change of scientific information and encourage co- 
operation between the scientific communities in 
each country, particularly in the life sciences. 
The research reported here by the Scholars covers 
the work supported by HHMI funding during the 
first grant year (July 1, 1991-March 30, 1992), and 
the publications listed are those that have resulted 
from these awards. 
Infection by animal rotaviruses is dependent on 
the interaction of the virions with sialic acid- 
containing structures on the surface of the target 
cell. In work reported by Carlos F. Arias, Ph.D. (Na- 
tional Autonomous University of Mexico, Cuerna- 
vaca) and his colleagues, the isolation and analysis 
of mutants that no longer depend on this interaction 
to be infective have revealed the existence of a 
novel site on the surface protein VP4 that is involved 
in the initial binding event, and probably penetra- 
tion of the virion into the cell as well. In addition, a 
new cleavage site has been identified on VP4 that 
could play an important role in the trypsin enhance- 
ment of rotavirus infectivity. 
Multicellular organisms have evolved communi- 
cation mechanisms to ensure orderly development, 
neural function, and ongoing differentiative pro- 
cesses in the adult. A breakdown in this process of 
cell-cell communication can lead to a variety of dis- 
eases, including cancer. The laboratory of Alan 
Bernstein, Ph.D. (Mount Sinai Hospital, Toronto) is 
interested in applying the techniques of molecular 
genetics to dissect the molecular pathways that con- 
trol these processes. Because cell-cell interactions 
take place in the intact animal, this group is taking 
various experimental approaches, involving analy- 
sis of existing mouse mutations and the generation 
of new mouse mutants carrying novel alterations in 
their germline. These approaches have led to the 
identification of several genes that encode a trans- 
membrane receptor, a factor that specifically binds 
to this receptor, and novel proteins involved in 
regulating gene expression that are centrally in- 
volved in a variety of developmental processes and 
malignancies. 
Several Salmonella typhi outer membrane pro- 
tein (OMP) genes have been isolated by the labora- 
tory of Edmundo Calva, Ph.D. (National Autono- 
mous University of Mexico, Cuernavaca). The 
structure and regulation of ompC, which codes for a 
major OMP, has been studied intensively. Molecular 
characterization of these OMPs and their genes 
should allow better understanding of the human im- 
mune response during typhoid fever and of some 
genetic regulatory features in this bacterium. Genes 
specific for the two species of Campylobacter 
(C. jejuni and C. coli) that most frequently cause 
diarrhea in humans have been isolated and are being 
characterized in order to define these species at the 
molecular level. 
Lactotropes comprise a heterogeneous popula- 
tion of prolactin-secreting cells in the vertebrate pi- 
tuitary gland. By using cultured pituitary cells from 
adult male rats as a model system, Gabriel Cota, 
Ph.D. (National Polytechnic Institute, Mexico City) 
and his colleagues have shown the existence of two 
functional subsets of lactotropes that differ in basal 
secretory activity. In addition, they have provided 
electrophysiological evidence for a differential ex- 
pression of voltage-gated ionic channels in the lac- 
totrope subtypes. Their results indicate that the se- 
cretory behavior of an individual lactotrope is 
largely determined by the activity of Na^ channels 
and high-threshold Ca^^ channels in its plasma 
membrane. 
In the process of fertilization, cell signaling is a 
matter of life and death. Understanding the molecu- 
lar mechanisms involved is the main goal of the labo- 
ratory of Alberto Darszon, Ph.D. (National Autono- 
mous University of Mexico, Cuernavaca). Ionic 
fluxes are fundamental in sperm activation and in 
the induction of the acrosome reaction. The sperm 
must undergo this reaction to fertilize the egg. By 
combining planar bilayer and patch-clamp tech- 
niques with measurements of intracellular pH and 
calcium, this group has established the presence of 
INTERNATIONAL RESEARCH SCHOLARS 495 
