Gene Offers New Lead in Cleft Lip and Palate
Research
Researchers supported by the National Institutes of Health report
in the current issue of the journal Science that a much-studied
gene called SUMO1, when under expressed, can cause cleft lip and
palate, one of the world’s most common birth defects.
With several genes already implicated in causing cleft lip and
palate, the authors note their addition to the list comes with
a unique biological twist. The SUMO1 gene encodes a small protein
that is attached to the protein products of at least three previously
discovered “clefting” genes during facial development, in essence
linking them into or near a shared regulatory pathway and now hotspot
for clefting.
“The big challenge for research on cleft lip and palate is to
move from studying individual genes to defining individual protein
networks,” said Dr. Richard Maas, a scientist at Brigham and Women’s
Hospital and Harvard Medical School and senior
author on the paper. His research is supported by NIH’s
National Institute of Dental and Craniofacial Research (NIDCR)
and the National Institute of General Medical Sciences (NIGMS).
“By protein network, I mean a nexus of proteins that interact
in a highly regulated way,” he continued. “It’s at this dynamic,
real-time level that science will begin to see the big picture
and tease out more of the needed insights to understand and hopefully
eventually prevent cleft lip and palate in newborns. What’s exciting
about SUMO1 is it allows us for the first time to begin to connect
at least some of the dots and hopefully lock into a highly informative
protein network that feeds into additional protein networks to
form the palate, or roof of the mouth.”
According to Maas, their discovery also offers a prime example
of the power of genomic research, the comparative study of individual
or sets of related genes among species, from yeast to human. The
discovery also highlights the utility of comprehensive gene databases,
DNA libraries, and other publicly accessible genomic resources
to accelerate the pace of modern science.
Maas said the work that led to this weeks’s Science paper began
several months ago when a clinician sent a blood sample from a
five-year-old patient who had been born with a cleft lip and palate
but no other obvious abnormalities. The sample arrived as part
of an international program in which Maas’s lab participates, called
the Developmental Genome Project, or DGAP.
Launched in the late 1990s, the NIGMS-supported project relies
on clinicians to send to DGAP-affiliated laboratories DNA samples
from consenting patients with birth defects that appear to be caused
by chromosome rearrangement, particularly so-called “balanced translocations.” A
balanced translocation means that during the normal cell cycle,
two chromosomes stick together, break, and form again incorrectly
with parts of each chromosome switching places.
“DGAP builds on the hypothesis that the translocation splits a
gene involved in the developmental process, renders it non functional,
and causes a visible birth defect,” said Dr. Fowzan Alkuraya, a
post-doctoral fellow in Maas’s laboratory and co-lead author on
the study. “In theory, the translocation will lead us to a biologically
informative gene. The challenge is to prove that theory and reality
are one and the same.”
As the first step in the process, Alkuraya and colleagues found
that the split gene in the patient’s DNA sample encoded SUMO1,
a small protein that is known to attach to the back of newly formed
proteins to modify their function. “This was intriguing news because
SUMO1 often attaches to, or tags, proteins to undergo a biochemical
process called sumoylation, which influences their behavior,” said
Maas. “At least three of the previously identified clefting genes
are known to be sumoylated and, if SUMO1 turned out to be involved
in clefting, it might lead us to a relevant protein network.”
To determine whether SUMO1 was indeed a clefting gene, the Maas
lab turned to their experimental model of choice, the mouse. After
establishing that SUMO1 is expressed in the region of the developing
mouse where the palate forms, the scientists asked the next logical
question: What happens if SUMO1 is expressed at abnormally low
levels as the palate forms?
The scientists turned to a research consortium called BayGenomics
that employs so-called “knockout,” or gene inactivation, technology
to for the systematic study of the individual genes with the mouse
genome to decipher their possible functions. The consortium, supported
by NIH’s National Heart, Lung, and Blood Institute (NHLBI), has
assembled a repository of embryonic stem cells for research purposes
in which each available line has a different gene knocked out,
or inactivated.
The Maas lab ordered the stem cell line in which SUMO1 had been
partially inactivated, implanted them into female mice, and waited.
The result: Four of 46 newborn mice had clefts of the palate or
face. “That’s about the incidence that we see in human families
with a history of cleft lip and palate,” said Dr. Irfan Saadi,
a co-lead author on the study and post-doctoral fellow in the Maas
lab. “So we weren’t put off by the low incidence at all. It’s what
we would have expected.”
In additional work, the scientists found that when SUMO1 and the
sumoylated clefting gene Eya1 were both inactivated, clefting increased
to 36 percent of newborn mouse pups, an indication that their proteins
interact during palate development and a point that additional
experiments further confirmed.
“Ten years ago, this work might have taken our laboratory years
to perform,” said Maas. “But with the genomic resources that are
now readily available, we can get answers in a matter of weeks
or months and, just as importantly, we spend a greater proportion
of our time thinking through the biology rather than worrying why
an assay isn’t working.”
With more tools and data to sift through, Maas noted that the
long held distinctions between syndromic and non-syndromic cleft
lip and palate have begun to blur. Traditionally, “syndromic” means
babies are born with cleft lip and/or palate, in addition to other
birth defects. “Non-syndromic” refers newborns who have cleft lip
and/or palate only.
“Clefting reflects the combined actions of multiple gene products,
rarely only one gene and its protein,” said Maas. “That’s why it’s
likely that what we now call non-syndromic has a very heterogenous
mixture of manifestations, too. It’s just that the other manifestations
are so subtle or not immediately obvious that we don’t recognize
them. Through our work and that of our colleagues, we can begin
to better define these conditions.”
The NIDCR (http://www.nidcr.nih.gov) is the nation’s leading
funder of research on oral, dental, and craniofacial health. The
NIGMS (http://www.nigms.nih.gov) supports basic biomedical research
that is the foundation for advances in disease diagnosis, treatment,
and prevention. The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov. |