Much of how the pancreas forms during human fetal development is a black box and even less is known about the pathways involved in genetic conditions affecting the pancreas. One such inherited condition is Mitchell-Riley Syndrome (MRS), a rare congenital disorder characterized by neonatal diabetes and an underdeveloped pancreas, caused by a recessive mutation in the regulatory RFX6 gene.
Patients with this devastating condition typically don’t survive beyond a year. However, research into the etiology of MRS has, until now, reached a standstill due to the lack of suitable animal models to study it; the RFX6 gene has a completely different function in mice.
In a first-of-its-kind study, a team of researchers led by Ray Dunn of A*STAR’s Skin Research Institute of Singapore (SRIS) have mapped how RFX6 influences pancreatic development in human tissues. This was made possible when co-author Bruno Reversade, a research director at the Genome Institute of Singapore (GIS) and the Institute of Molecular and Cell Biology (IMCB), identified a family with a rare lineage: both parents were healthy carriers for the RFX6 mutation, while their four daughters had been diagnosed with MRS.
“We sought to ask the simple (and unanswered) question of what the etiology of the MRS phenotype is, or simply when do things go wrong during pancreatic development (during human gestation) without a functional RFX6 gene to give rise to such a lethal phenotype,” explained Dunn.
To answer this question, Dunn and colleagues generated induced pluripotent stem cells (iPSCs)—adult skin or blood cells that have been reprogrammed to display characteristics of embryonic stem cells—using cells isolated from two of the daughters and their father. These iPSCs were cultured in factors to promote pancreatic development and analyzed to track gene expression patterns during this process. Additionally, they also compared tissues from a 12-week-old fetus with the RFX6 mutation to a healthy fetus of the same age using micro-CT scanning.
The researchers found that RFX6 expression peaks on day eight of in vitro differentiation, which coincides with the expressions of PDX1 and SOX9, two signature genes associated with pancreatic tissue development. In the absence of RFX6, PDX1 and SOX9 expressions were significantly reduced, negatively impacting the efficiency of pancreatic endoderm development and resulting in a severely underdeveloped pancreas without endocrine cells.
“We now know precisely when RFX6 is required during human pancreatic development. This is fundamental knowledge about how organs develop in humans,” shared Dunn. “What we found gives individuals who are carriers access to genetic counseling and prenatal screening. The family described in our paper opted to terminate their fourth pregnancy to avoid the anguish of having yet another newborn succumb to MRS.”
The team is continuing to explore the role of RFX6 in other aspects of human development. “Since RFX6 is expressed in many other organs, we’re curious what role RFX6 plays outside of the pancreas,” said Dunn.
The A*STAR-affiliated researchers contributing to this research are from the Skin Research Institute of Singapore (SRIS), Institute of Molecular and Cellular Biology, and the Genome Institute of Singapore.