Ph.D. - University of Kentucky, 1999
Telephone: (301) 405-7562
Fax: (301) 314-9489
Research Interests: Host-pathogen interactions; Molecular/cellular
mechanisms of Mycobacteria pathogenesis
Infections caused by Mycobacteria remain a major human health
problem. Mycobacterium tuberculosis alone infects ~1/3 of
the world's population and causes 2-3 million deaths each year.
Further threats come from the emergence of multi-drug resistant
strains and co-infections with AIDS patients, which awaits desperately
the development of new generation treatment and prevention of the
infections. Given the significance of the disease and decades of
research effort, the molecular and cellular mechanisms of Mycobacteria
pathogenesis remain largely unknown. This is in large part due to
the extremely slow growth rate of M. tuberculosis, its strict
requirement for laboratory containment, and lack of opportune tools
for the studies. We have developed a M. marinum-zebrafish
infection model that has significantly advanced the study of Mycobacteria
pathogenesis. M. marinum infects fish and frogs naturally
with many pathological features similar to human tuberculosis. We
have compelling evidence demonstrating that the M. marinum-zebrafish
model is reliable, facile, safe, and rapid for studying molecular
and cell biology of Mycobacteria pathogenesis and host responses
to the infections.
Being intracellular pathogens primarily infecting host macrophages,
Mycobacteria have evolved complex parasitic lifestyle and
sophisticated mechanisms to combat host defense machinery. For example,
Mycobacteria utilize multiple macrophage receptors for efficient
invasion of the cells. Within macrophages, Mycobacteria inhibit
acidification of the bacteria-containing phagosome and its maturation
to phago-lysosome. For optimal intracellular growth, Mycobacteria
inhibit macrophage apoptotic cell death program and undergo profound
alterations of gene expression and secretion of bacterial toxins
to modulate host defense mechanisms. Furthermore, Mycobacteria
are able to spread from a cell to another and to cause dissemination
of infection. The molecular mechanisms underlining those processes
are just beginning to be understood. We have exploited the M.
marinum model and successfully developed transposon mutagenesis
to identify Mycobacteria genes necessary for 1) invasion
of macrophages; 2) intracellular replication in macrophages;
3) inhibition of macrophage apoptosis; 4) regulation
of Mycobacteria gene expression; 5) secretion of Mycobacteria
cyto-toxins; and 6) Mycobacteria cell-to-cell spread
and dissemination of infection. We have characterized many of these
genes in detail. One of our significant findings is our demonstration
that for all of the M. marinum mutants tested we could successfully
complement their defects by expressing corresponding M. tuberculosis
gene homologues, demonstrating the relevance and strength of this
model. Our studies have extended significantly current knowledge
of the molecular and cellular mechanisms of Mycobacteria
Among the M. marinum genes that we first characterized is
kasB encoding an enzyme catalyzing the elongation of mycolic
acids, which are major components of the Mycobacteria cell
wall crucial for protection of the bacteria. We have shown that
inactivation of kasB not only significantly reduces bacterial
intracellular growth in macrophage but also renders the bacteria
hypersensitive (over 100-fold) to antibiotics. Further studies to
develop novel drugs targeting kasB for therapeutic treatment
of multi-drug resistant Mycobacteria are greatly warranted.
A second locus studied in detail is mip that contains two
genes required for Mycobacteria to both invade
and persist in macrophage. Recently, we have characterized
in detail a third gene cluster of ~20 genes that are required for
Mycobacteria to spread from cell to cell in cell cultures
and to cause disseminated infection in zebrafish. Further studies
of this gene cluster have revealed that their encoded proteins constitute
a novel protein secretion system for exporting Mycobacteria
cyto-toxins that resolve the bacteria-containing phagosome membrane
to promote Mycobacteria cell-to-cell spread via actin-based
motility, similar to Listeria. This gene cluster extends
beyond a previously described M. tuberculosis virulence locus
RD1 and is thereby named extRD1 (extended RD1). Ongoing research
on extRD1 addresses the following important questions: 1)
What are the cyto-toxins secreted by extRD1 required for resolution
of the bacteria-containing phagosome membrane? 2) How do
the cyto-toxins interact with and resolve the host cell membrane?
3) How do the cyto-toxins contribute to disseminated infection
in the host? and 4) How are cyto-toxins secreted by the extRD1
secretion system. These studies will be carried out using our established
M. marinum-zebrafish model system, and meanwhile the significant
findings will be confirmed in the M. tuberculosis system
and applied to development of more efficient treatment and prevention
of M. tuberculosis infection. Finally, one of our long-term
goals is to use the M. marinum-zebrafish model to study Mycobacteria
persistence, reactivation, and transmission.
Gao L.Y., Guo S., Morisaki H., Horwitz M.A., Engel J.N., and Brown
E.J. (2004). A mycobacterial virulence gene cluster extending RD1
is required for cytolysis, bacterial spreading, and ESAT-6 secretion.
Mol. Microbiol. 53(6):1677-1693.
Gao L.-Y., Laval F., Lawson E.H., Groger R.K, Woodruff A., Morisaki
J.H., Cox J.S., Daffe M., and Brown E.J. (2003). Requirement for
kasB in Mycobacterium Mycolic Acid Biosynthesis, Cell
Wall Impermeability, and Intracellular Survival: Implications for
therapy. Mol. Microbiol. 49(6):1547-1563.
Stamm L.M., Morisaki J.H., Gao L.-Y., Jeng R.L., McDonald K.L.,
Roth R., Takeshita S., Heuser J., Welch M.D., and Brown E.J. (2003).
Mycobacterium marinum Escapes from Phagosomes and Is Propelled
by Actin-based Motility. J. Exp. Med. 198(9):1361-1368.
Gao L.-Y., Groger R., Cox J.S., Beverley S.M., Lawson E.H., and
Brown E.J. (2003). Transposon Mutagenesis of Mycobacterium marinum
Identifies a Locus Linking Pigmentation and Intracellular Survival.
Infect. Immun. 71(2):1-8.
Gao, L.-Y. and Abu Kwaik, Y. (2000). Modulation of host cell apoptosis
by intracellular bacterial pathogens. Trends Microbiol. 8(7):306-313.
Venkataraman, C., Gao, L.-Y., Bondada, S., and Abu Kwaik, Y. (1998).
Identification of putative cytoskeletal protein homologues in the
protozoan host Hartmannella vermiformis as substrates for
induced tyrosine phosphatase activity upon attachment to the Legionnaires'
disease bacterium, Legionella pneumophila. J. Exp. Med. 188:505-514.
Gao, L.-Y., Harb, O.S., and Abu Kwaik, Y. (1998). Identification
of macrophage-specific infectivity loci (mil) of Legionella
pneumophila that are not required for infectivity of protozoa.
Infect. Immun. 66:883-892.
1. Postdoctoral position: A Postdoctoral position is immediately
available for highly motivated and qualified individuals to study
the molecular and cellular mechanisms of Mycobacteria pathogenesis.
Projects will involve studying how Mycobacteria escape from host
cell phagosome and spread from cell to cell and how these processes
contribute to pathogenesis of the infection. The successful applicants
will need to demonstrate expertise in, via publications in internationally
recognized peer-reviewed journals: 1) microbial genetics, 2) standard
molecular biology skills including DNA and protein works, and 3)
cell biology skills including cell culture and microscopy. Certain
experience with human or animal subjects and the cells is a plus.
Qualified candidates should have a Ph.D. degree with excellent oral
and written communication skills. Salary will be commensurate with
experience. The University of Maryland at College Park is the flagship
campus of the University of Maryland System. It occupies a beautiful
1,500 acre campus in the heart of the Washington-Baltimore high-tech
corridor. Please send curriculum vitae and a brief letter with three
names of reference to:
Lian-Yong Gao, Ph.D.
Department of Cell Biology and Molecular Genetics
3109 Microbiology Building
University of Maryland
College Park, MD 20742
2. Graduate Research Assistantships: My lab has 2-3 new
openings for graduate student research assistants and will provide
outstanding individual research projects for them. Please contact
me for possible lab rotations.