A MEN1 pancreatic neuroendocrine tumour mouse model under temporal control

Abstract

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterised by occurrence of parathyroid tumours and neuroendocrine tumours (NETs) of the pancreatic islets and anterior pituitary. The <i>MEN1</i> gene, encoding menin, is a tumour suppressor, but its precise role in initiating <i>in vivo</i> tumourigenesis remains to be elucidated. The availability of a temporally controlled conditional MEN1 mouse model would greatly facilitate the study of such early tumourigenic events, and overcome the limitations of other <i>MEN1</i> knockout models, in which menin is lost from conception or tumour development occurs asynchronously. To generate a temporally controlled conditional mouse model, we crossbred mice with the MEN1 gene floxed by LoxP sites (<i>Men1</i><i>^L/L</i> ), and mice expressing tamoxifen-inducible Cre recombinase under the control of the rat insulin promoter (<i>RIP2-CreER</i>), to establish a pancreatic β-cell-specific NET model under temporal control (<i>Men1</i><i>^L/L</i> /<i>RIP2-CreER</i>). <i>Men1</i><i>^L/L</i> /<i>RIP2-CreER</i> mice aged ~3 months were given tamoxifen in the diet for 5 days, and pancreata harvested 2-2.5, 2.9-3.5 and 4.5-5.5 months later. Control mice did not express <i>Cre</i> and did not receive tamoxifen. Immunostaining of pancreata from tamoxifen-treated <i>Men1</i><i>^L/L</i> /<i>RIP2-CreER</i> mice, compared to control mice, showed at all ages: loss of menin in all islets; increased islet area (>4.2-fold); increased proliferation of insulin immunostaining β-cells (>2.3-fold) and decreased proliferation of glucagon immunostaining α-cells (>1.7-fold). There were no gender and apoptotic or proliferation differences, and extra-pancreatic tumours were not detected. Thus, we have established a mouse model (<i>Men1</i><i>^L/L</i> /<i>RIP2-CreER</i>) to study early events in the development of pancreatic β-cell NETs.