Using genetic techniques, investigators at Weill Cornell Medical College have managed to successfully repaired cleft lips in mice embryos specially engineered for the investigation of cleft palate and cleft lip. This novel breakthrough might reveal how to prevent or treat the condition in humans.
Cleft lip and cleft palate are one of the most prevalent birth defects. Treatment for these defects involves multiple surgeries, orthodontics as well as speech therapy. So far, very few pre-clinical techniques have allowed scientists to investigate the molecular causes of these defects. In particular, there have been insufficient animal models that precisely reflect the contribution of multiple genes to these congenital defects in humans.
In a recent study published in the journal Developmental Cell, the first multigenic mouse model of cleft lip with or without cleft palate was reported by Dr. Licia Selleri, associate professor of cell and developmental biology at Weill Cornell Medical College, and her co-authors. The study revealed the role of genes for Pbx (Pre-B Cell Leukemia Transcription Factor) proteins in regulating cellular signaling behaviors vital for these deformities to develop. Furthermore, the team found that changing one type of molecule within the Wnt signaling pathway (that consists of a network of proteins best known for their roles in embryogenesis) is enough to correct the abnormalities.
For several years Dr. Selleri has studied Pbx proteins. In a prior investigation Dr. Selleri showed how Pbx proteins were involved in organ and skeletal development. In her most recent investigation, Selleri and her colleagues, including postdoctoral fellows Drs. Elisabetta Ferretti and Bingsi Li, used mutant mice that lacked various combinations of three Pbx genes in the ectoderm (the embryonic cell layer that give rise to the nose and lip), in order to examined if Pbx proteins also contribute to facial development.
They discovered that in all of the mouse embryos with these compound mutations, only mutations affecting multiple Pbx genes resulted in complete cleft lip, with or without cleft palate. Dr. Selleri explains:
“This finding differs from those of previous studies using other mammal models of these conditions, in which a mutation in a single gene produced defects in only some of the animals. The role of Pbx genes in the development of the shape of the face is a new and surprising finding.”
In addition, the team found that mouse embryos with multiple Pbx mutations had either reduced of absent Wnt activity, which plays a vital role in the development of the embryo, within the ectoderm. First author of this investigation, Dr. Ferretti, discovered that Pbx genes coordinate a chain of signaling molecules associated in cleft lip with or without cleft palate, including, fibroblast growth factors, Wnt, p63 as well as interferon regulatory factor 6 (Irf6) – signaling pathways that exist across mammal species. When this network was disturbed, results to a decrease in programmed cell death, hampering with the proper fusion of facial tissues and resulting in cleft lip.
Amazingly, the cleft lips in all of these animals completely disappeared when Dr. Li, second author of the investigation, used genetic techniques to restore Wnt activity in the ectoderm of mouse embryos within compound Pbx mutations. Dr. Selleri explains:
“To my knowledge, this is the first time that anyone has corrected this defect in embryos, and we really show here that Wnt is a critical factor. This is a very provocative result because it opens a completely new avenue of strategies for tissue repair.”
In order to follow up on this investigation, Dr. Selleri plans to examine if adding Wnt molecules to Pbx-mutate mouse embryos placed within an environment that mimics the uterus is enough to prevent or correct the defects. Dr. Selleri said: “compared with genetic manipulations, this approach of delivering Wnt signals directly to the uterus would be more realistic for implementation in humans.”
Dr. Selleri, has now collaborated with Jason Spector, assistant professor of plastic surgery at Weill Cornell Medical College and with Larry Bonassar, associate professor of biomedical engineering at Cornell University, in order to conceive Wnt-related techniques for tissue repair, such as tissue implants designed to deliver Wnt molecules to correct abnormalities without the need for multiple surgeries, either in the utero prior to birth of the fetus, or after birth.
Further investigation collaborators include Rediet Zewdu and Victoria Wells of Weill Cornell Medical College; Jean M. Hebert of Albert Einstein College of Medicine in the Bronx, N.Y.; Courtney Karner of the University of Texas, Southwestern Medical Center, in Dallas, Texas; Matthew J. Anderson of the National Cancer Institute in Frederick, Md.; Trevor Williams of the University of Colorado, Denver; Jill Dixon and Michael J. Dixon of the University of Manchester in the U.K.; and Michael J. Depew of King’s College London in the U.K.
The study was supported by a Marie Curie Fellowship, the Medical Research Council in the U.K., the Royal Society, King’s College London, March of Dimes and Birth Defects Foundation, the National Institutes of Health, the Cleft Palate Foundation, and the Alice Bohmfalk Trust.
Written by Grace Rattue