Analysis of Urocortin 2 overexpressing mice

Urocortin 2 (UCN2) is a recently identified neuropeptide whose functions still remain to be elucidated. It comprises 38 amino acids and belongs to the corticotropin-releasing hormone (CRH) family of neuropeptides which also includes corticotropin- releasing hormone (CRH), Urocortin (UCN) and Urocortin 3 (UCN3). These four CRH-related neuropeptides signal through two heptahelical G-protein coupled receptors, CRH receptor type 1 (CRHR1) and CRH receptor type 2 (CRHR2). UCN2 was found to be a specific, high affinity agonist for CRHR2, just as UCN3, whereas CRH shows a binding preference for CRHR1. UCN is bound with approximately the same affinity by both receptors. Until today exact functions that are mediated through the activation of CRHR2 are not completely understood. CRHR2 expression in the brain is restricted to specific areas and CRHR2 is widely expressed in the periphery. In contrast CRHR1 is broadly distributed throughout the brain. It has been shown that CRHR2 activation is involved in feeding behaviour, anxiety, locomotion, the cardiovascular system, gastrointestinal function and metabolism. To reveal the functions of CRHR2 and its specific agonist UCN2 we created a conditional UCN2 overexpressing mouseline. Using homologous recombination in ES-cells mice were generated which express a Ucn2 IRES LacZ construct under the control of the ubiquitously active ROSA26 (R26) promotor. For conditional activation, a floxed stop-cassette terminating transcription was inserted between the promotor and the cDNA of Ucn2 and LacZ. These mice are called R26^stopUcn2. To overexpress UCN2 in the central nervous system (CNS) R26^stopUcn2 mice were bred with a mouseline which expresses Cre recombinase under the control of the nestin promotor. We could show that in offspring of these mice LacZ and UCN2 are expressed in the entire CNS. To elucidate the functions of UCN2 we analyzed UCN2 overexpressing mice in more detail performing expression analysis and behavioural tests.