Page 72 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
Research Area in the field of biomedical research and contribute to our understanding of the role of gene function in human
health and disease.
Disruption of a novel mouse gene,
causes juvenile communicating hydrocephalus.
Oliver K. Appelbe
Bryan Bollman
Ali Attarwala
Lindy A. Triebes
Daniel J. Curry
Jennifer V. Schmidt
. 1)
Department of Biological Sciences, University of
Illinois at Chicago, Chicago, IL; 2) Department of Neurosurgery, Baylor College of Medicine, Houston, TX.
Juvenile hydrocephalus, the accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain, affects 1 in 500 newborns,
causing significant morbidity among human children. Hydrocephalus may result from overproduction, decreased absorption, or
restricted flow of CSF. Few genetic causes of this disease are known in humans, and animal models can therefore aid in
identifying candidate genes and studying relevant pathways. The Juvenile hydrocephalus (
mouse line carries a transgenic
insertional mutation on chromosome 9 that disrupts a previously unstudied gene. The integrated
reporter gene is expressed
in the pineal gland, hypothalamus, ventricular ependyma and choroid plexus. The mutation appears to act as a loss of function,
with homozygous
mice exhibiting externally detectable hydrocephalus by two weeks of age and few animals surviving
beyond six weeks. Histological analysis of
mice shows a patent aqueduct, indicating communicating hydrocephalus, with no
overt brain morphological changes. Scanning electron microscopy found reduced density and loss of orientation of ventricular
ependymal cilia, which suggests loss of ciliary-mediated CSF flow. Current research is directed at characterizing the ciliary
phenotype of
mice, as well as determining the normal function of the
Role of miR-155 in BRCA1-mediated tumorigenesis.
Suhwan Chang,
Shyam K. Sharan
Mouse Cancer Genetics Program,
Frederick National Lab. NCI, Frederick, MD. USA.
To date, inheritance of a mutant BRCA1 or BRCA2 gene is the best-established indicator of an increased risk of developing
breast cancer, the most frequently diagnosed cancer in women. We have developed a mouse embryonic stem cell based assay to
examine the functional consequences of variants identified in these genes. The assay is based on the ability of human BRCA1 or
BRCA2 to complement the loss of endogenous genes in mouse embryonic stem cells. Using this assay, we have characterized
R1699Q, a low risk variant of BRCA1. Interestingly, this variant affects ES cell survival but exhibits no defect in genomic
stability or cell cycle regulation. We have used this variant to uncover a novel role for BRCA1 in regulation of an oncogenic
microRNA, miR-155. Our studies revealed a strong correlation between BRCA1 deficiency and miR-155 up-regulation in murine
as well as human BRCA1-deficient tumors. We also found that over-expression of miR-155 augmented tumor growth whereas
the knockdown of miR-155 attenuated the growth of BRCA1-deficient tumor cell lines in mice. These findings suggest that mir-
plays an oncogenic role in BRCA1-mediated mammary tumorigenesis. To test this, we generated a cohort of Brca1-mutant
mice that are deficient in miR-155. Mice lacking miR-155 are viable and fertile but have severe defects in the T cells, B cells and
dendritic cell function. To examine the effect of mir-155 loss on Brca1-mediated mammary tumorigenesis, we have characterized
Brca1; Trp53 conditional knockout mice with a K14-Cre transgene to delete the conditional allele in the epithelial cells. These
mice have been shown to develop mammary tumors that are histopathologically similar to human BRCA1-mutant breast tumors.
Surprisingly, loss of miR-155 did not reveal any effect on the tumor latency or tumor free survival of the mouse. We are now
examining why knockdown of miR-155 in tumor cells resulted in suppression of tumor growth in an allograft model but germline
loss of miR-155 function has no effect on spontaneous mammary tumorigenesis. We will describe our findings that suggest a role
for miR-155 in the tumor microenvironment. These findings can have important implications on the use of anti-miR-155 agents
for cancer therapy.
Conditional deletion of bA3/A1-crystallin in RPE shows decreased lysosomal activity and drusen-like deposits in mouse
eyes. Debasish Sinha
Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD.
The Retinal Pigmented Epithelium (RPE) serves many physiological roles that are crucial for maintaining homeostasis of the
retina. The RPE is one of the most active phagocytic cell types in the body, phagocytosing 10% of total photoreceptor volume
daily. Autophagy, a process by which cellular constituents are degraded and recycled as part of normal cellular remodeling, is
likely to be of particular importance in post-mitotic cells with high metabolic demand, such as the RPE. Therefore, proper
functioning of the RPE requires that both phagocytosis and autophagy be in balance, as perturbation of either process can lead to
some manifestations of age-related macular degeneration (AMD). AMD is the leading cause of legal blindness in developed
countries. We recently reported that A3/A1-crystallin, a lens structural protein, is expressed in RPE cells and trafficked to
lysosomes, where it is involved in degradation of ingested photoreceptor outer segments (OS) and also in autophagy. We have
recently generated a conditional knockout (cKO) mouse whereA3/A1-crystallin has been deleted from the RPE. The expression
levels of proteins known to be involved in movement of autophagosomes along microtubules for fusion with lysosomes remain
unchanged. However, autophagosome-lysosome fusion studies, in which RPE cells were labeled with mCherry-LC3II
autophagosome) and LAMP1-YFP (lysosome) suggest a possible defect in the fusion process in cells lacking functional A3/A1-
crystallin. Moreover, Rab7 GTPase, Rab-interacting lysosomal protein, and lysosome-associated membrane proteins 1 and 2, are
decreased in A3/A1-crystallin deficient RPE cells. Our data also show that the activity of Cathepsin D is decreased in RPE cells
that lack functional A3/A1-crystallin and have drusen-like deposits. Lysosomal dysfunction is assumed to play an essential role
in the formation of drusen, which trigger neovascular and atrophic reactions in AMD. Autophagy and phagocytosis may be