Researchers discover how patients with mutations in DNA sequences develop pancreatic malformations

Researchers at the Center for Genomic Regulation (CRG) have identified a DNA sequence critical to pancreatic differentiation and function and described for the first time how it works.

Patients with mutations in the DNA sequence called EnhP develop pancreatic malformations. This is by far the clearest example of an inherited disease caused by mutations that do not destroy the gene’s DNA sequence.

Diseases caused by single DNA sequence mutations, such as Huntington’s disease and sickle cell anemia, are known as monogenic diseases. In most cases, such mutations disrupt the protein-encoding gene. In this case, the EnhP mutation disrupts a single ‘enhancer’ rather than a single gene.

Our genome contains hundreds of thousands of DNA elements thought to function as enhancers. These enhancer DNA sequences act as switches to turn on transcription of target genes in the appropriate tissues.

According to the authors of the study published today, developmental cells, EnhP is not the only enhancer defect that causes disease. Mutations in enhancers may be the cause of monogenic disease in many patients in whom laboratory testing failed to reveal the causative gene mutation.

Understanding the role of enhancers in disease could change the way we practice medicine.

Clinical genetics is moving from sequencing protein-coding genes to sequencing the whole genome. While it remains difficult to identify which parts of the genome are truly vulnerable to mutation, it is theoretically possible to discover disease-causing mutations outside conventional regions of the genome. It is now possible.

Jorge Ferrer, PhD, senior author of the study, coordinator of CRG’s Medical Genomics Transversal Program and group leader of CIBERDEM

Researchers had previously discovered EnhP while studying developmental disorders in 10 different families. Working with a team in Exeter, UK, they found that enhancer mutations are the most common cause of pancreatic agenesis, a rare congenital disorder that causes loss of pancreatic tissue and neonatal diabetes.

In this study, the researchers extended previous work to explain why this particular enhancer is vulnerable to disease-causing mutations. A mouse model was genetically engineered to study the effects. Mice lacking both copies of EnhP are born with severe underdeveloped pancreas and insulin-deficient diabetes. They also studied human stem cells in vitro.

They show that EnhP functions by increasing the rate of transcription of a nearby gene known as pancreas-associated transcription factor 1a (PTF1A). More specifically, this study reveals that EnhP’s sole role is to activate a whole cluster of enhancers that also regulate her PTF1A in the first cells to form the pancreas during fetal development. became. Activation of these other enhancers and turn-on of PTF1A transcription initiates a cascade of molecular events that lead to the formation of normal pancreatic cells.

“We show that enhancers function hierarchically, and this is at the top,” says Dr. Ferrer. It resolves the paradox that there are multiple other enhancers that control the same gene. Finding them will help us understand which enhancers are vulnerable to a variety of other causative mutations.

The findings also have implications for efforts to generate insulin-producing beta cells in the laboratory. Cell transplantation is a viable option for diabetics, but the demand for functional cells from dead donors far exceeds supply.

Growing beta cells in culture is one way to address this challenge, but they rarely share the same functional characteristics as normal human beta cells. This is because we do not know the mechanisms required for proper differentiation.

“EnhP triggers the molecular programs necessary for the proper formation of human beta cells. This knowledge can be used to improve laboratory conditions for creating beta cells,” concludes Dr. Ferrer. .

This work was supported by the Spanish Ministry of Science and Innovation, Wellcome Trust, CIBERDEM, and the European Research Council. This work was co-led by his first co-authors Irene Miguel-Escalada, Miguel Ángel Maestro, Diego Balboa, and senior author Jorge Ferrer.