BOORSE, GC; DENVER, RJ; Univ. of Michigan, Ann Arbor: Tissue distribution of corticotropin-releasing hormone (CRH) signaling components in Xenopus laevis suggests multiple roles in physiology and development

The distribution and actions of CRH extend beyond the regulation of the hypothalamo-pituitary-adrenal axis. By contrast to mammals, little is known about the peripheral expression or functions of CRH in nonmammalian vertebrates. We analyzed, by RT-PCR, the distribution of mRNAs for CRH signaling components (CRH, CRHRs and CRHBP) in X. laevis. Analysis of tissues from juveniles showed the presence of CRH, CRHR, and CRHBP mRNAs in the following: brain, pituitary, heart, kidney, intestine, lung, stomach and ovary. CRHR2 is ubiquitously expressed while CRHR1 is expressed in only a subset of tissues. Fat, skin and pancreas express CRH and CRHR2 but not CRHBP or CRHR1. Spleen and liver express only CRH mRNA, while we found no evidence for any CRH signaling component in muscle or blood. Radioimmunoassay (RIA) showed the presence of CRH immunoreactivity (CRH-ir) in brain, heart and skin. In the tadpole, previous research showed that CRHBP mRNA is strongly upregulated by thyroid hormone (TH) during metamorphic climax in the tail, but not in the brain. We hypothesized that other CRH signaling components are expressed in the tadpole tail and that CRH may have local effects, either on tail growth or regression. Both CRH and CRHR1 mRNAs are expressed in the tail throughout development. Additionally, RIA showed CRH-ir in tadpole tail. All of the CRH signaling components are expressed in tail muscle, but not tailfin. The upregulation of CRHBP mRNA by TH can be replicated in tail explant cultures, and we are currently investigating roles for CRH in the tadpole tail. Our findings suggest that CRH plays multiple roles in physiology and development in X. laevis. (supported by NSF grant IBN9974672 to RJD and NSF predoctoral fellowship to GCB)