The St Jude investigators discovered that, in mice, the p107 gene is active before birth in the cells that are fated to produce the mature retina. This gene ensures that the retinal cells stop multiplying at the correct time during development of this tissue. The Rb gene is expressed after birth in actively multiplying retinal cells.
The study showed that if gene mutations knock out both p107 and Rb, the mice are at high risk of developing retinoblastoma. But if only p107 is knocked out, Rb can make up for that loss and prevent retinoblastoma; and if Rb is knocked out, p107 becomes more active to make up for that loss.
In the human retina, however, p107 is almost completely inactive, leaving RB1 to do most of the work. RB1 is the human equivalent of Rb in mice. Therefore, if RB1 suffers a mutation and becomes inactive, there is no backup gene in the human retina as there is in the mouse. Therefore the result of such an RB1 failure is likely to be retinoblastoma.
“If we could figure out how to turn on the human p107 gene, it might be able to protect against retinoblastoma when RB1 is mutated,” said Dr Stacy Donovan, a postdoctoral fellow in the department of developmental neurobiology at St Jude.
“Studying mouse models of retinoblastoma might also let us discover which of the various types of cells in the retina becomes cancerous and causes retinoblastoma,” added Dr Brett Schweers, a postdoctoral fellow in the department of developmental neurobiology at St Jude. “Knowing which cell causes retinoblastoma would give researchers a specific target for a novel retinoblastoma drug.”
The results of the study appear in the open-access journal BMC Biology.