Probes for INS

Loss of pancreas β-cell function is the precipitating factor in all forms of diabetes. Cell replacement therapies, such as islet transplantation, remain the best hope for a cure; however, widespread implementation of this method is hampered by availability of donor tissue. Thus, strategies that expand functional β-cell mass are crucial for widespread usage in diabetes cell replacement therapy. Here, we investigate the regulation of the Hippo-target protein, Yes-associated protein (Yap), during development of the endocrine pancreas and its function after reactivation in human cadaveric islets. Our results demonstrate that Yap expression is extinguished at the mRNA level after neurogenin-3-dependent specification of the pancreas endocrine lineage, correlating with proliferation decreases in these cells. Interestingly, when a constitutively active form of Yap was expressed in human cadaver islets robust increases in proliferation were noted within insulin-producing β-cells. Importantly, proliferation in these cells occurs without negatively affecting β-cell differentiation or functional status. Finally, we show that the proproliferative mammalian target of rapamycin pathway is activated after Yap expression, providing at least one explanation for the observed increases in β-cell proliferation. Together, these results provide a foundation for manipulating Yap activity as a novel approach to expand functional islet mass for diabetes regenerative therapy.

The pituitary gland is a primary endocrine organ that controls major physiological processes. Abnormal development or homeostatic disruptions can lead to human disorders such as hypopituitarism or tumours. Multiple signalling pathways, including WNT, BMP, FGF and SHH regulate pituitary development but the role of the Hippo-YAP1/TAZ cascade is currently unknown. In multiple tissues, the Hippo kinase cascade underlies neoplasias; it influences organ size through the regulation of proliferation and apoptosis, and has roles in determining stem cell potential. We have used a sensitive mRNA in situ hybridisation method (RNAscope) to determine the expression patterns of the Hippo pathway components during mouse pituitary development. We have also carried out immunolocalisation studies to determine when YAP1 and TAZ, the transcriptional effectors of the Hippo pathway, are active. We find that YAP1/TAZ are active in the stem/progenitor cell population throughout development and at postnatal stages, consistent with their role in promoting the stem cell state. Our results demonstrate for the first time the collective expression of major components of the Hippo pathway during normal embryonic and postnatal development of the pituitary gland.