Jigsaw Mutation Critical Piece of Notch Pathway Puzzle
The Notch pathway helps determine cell fate, differentiation and proliferation. How it accomplishes these tasks has been a puzzle. But now research has identified a key a specific domain within Notch critical to determining which ligand Notch will bind with
The work was led by researchers at Baylor College of Medicine (BCM) and the Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital. Their finding provides researchers with a molecular handle on which to base future studies of this critical protein.
A report on their work appears online in the journal Science.
Misregulation of Notch signaling
is seen in various types of cancers
and numerous human diseases.
The Notch receptor can be activated by
binding to two families of ligands,
Serrate and Delta.
Since different ligands have different consequences
on signal activation depending on context,
understanding how Notch discriminates
Serrate and Delta is crucial.
Significance of EGF repeats
Most of the Notch receptor is composed of what scientists call EGF repeats (epidermal growth factor-like repeats). Previous studies have suggested that the key to Notch signalling lies within these repeats.
"We don’t know the function of most of these EGF repeats on Notch, and there are 36 EGF repeats. Some are needed to bind to both the Serrate and Delta ligand families, while others are required to bind to only one." said Dr. Shinya Yamamoto, a former graduate student from the Program in Developmental Biology and currently a postdoctoral fellow in the laboratory of Dr. Hugo Bellen, director, Program in Developmental Biology and professor of molecular and human genetics and neuroscience at BCM.
Indeed, mutations in these repeats have been found in
patients with Cerebral Autosomal Dominant Arteriopathy
with Subcortical Infarcts and Leukoencephalopathy
(CADASIL), a hereditary stroke disorder;
Alagille syndrome, a genetic disorder affecting the liver,
heart, skeleton, eye and other organs;
aortic valve disease, and squamous cell carcinoma.
In studies in fruit flies (Drosophila melanogaster),
Yamamoto and colleagues screened for mutated
alleles (which are alternative forms of a gene) of Notch
and focused on a mutation that they named Jigsaw.
Flies with this mutation have normal bristles on their
thorax but defects in the wing.
The research showed the Notch gene exhibited defects
in its ability to bind to Serrate but not to Delta.
They also saw a similar mutation in mouse
Notch2 failing to signal in response to Jagged,
the mammalian homolog of Serrate.
Yamamoto: "Structural biologists will now have a molecular handle with which to begin investigating the molecular basis of ligand selectivity at the atomic level. Others may consider EGF repeat 8 as a potential drug target for small molecules and monoclonal antibodies."
Notch signaling affects many developmental and cellular processes and has been implicated in congenital disorders, stroke, and numerous cancers. The Notch receptor binds its ligands Delta and Serrate and is able to discriminate between them in different contexts. However, the specific domains in Notch responsible for this selectivity are poorly defined. Through genetic screens in Drosophila, we isolated a mutation, Notchjigsaw, that affects Serrate- but not Delta-dependent signaling. Notchjigsaw carries a missense mutation in epidermal growth factor repeat-8 (EGFr-8) and is defective in Serrate binding. A homologous point mutation in mammalian Notch2 also exhibits defects in signaling of a mammalian Serrate homolog, Jagged1. Hence, an evolutionarily conserved valine in EGFr-8 is essential for ligand selectivity and provides a molecular handle to study numerous Notch-dependent signaling events.
Others who took part in this study include Wu-Lin Charng; Manish Jaiswal; Vafa Bayat; Bo Xiong; Ke Zhang; Hector Sandoval; Gabriela David and Hao Wang, all of BCM; and Robert Haltiwanger, Nadia Rana and Shinako Kakuda, all of Stony Brook University, Stony Brook, NY.
Funding for this work came from the National Institutes of Health; the BCM Intellectual and Developmental Disabilities Research Center; the Nakajima Foundation; the Taiwan Merit Scholarships Program of the National Science Council; the Edward and Josephine Hudson Scholarship Fund; the Houston Laboratory and Population Science Training Program in Gene-Environment Interaction of the Burroughs Wellcome Fund; and the Houston Research Education and Career Horizon Institutional Research and Academic Career Development Award.
Bellen is also a Howard Hughes Medical Institute Investigator. He holds the March of Dimes Chair in Developmental Biology and is Charles Darwin Professor in Genetics at Baylor College of Medicine.
Original article: http://www.bcm.edu/news/item.cfm?newsID=6559