Meeting Abstract

17.3  Monday, Jan. 4  REGULATION OF DEVELOPMENT BY CORTICOTROPIN RELEASING HORMONE IN DIRECT DEVELOPING FROG ELEUTHERODACTYLUS COQUI KULKARNI, Saurabh*; ELINSON, Richard; SINGAMSETTY, Shrikanth; BUCHHOLZ, Daniel; University of Cincinnati; Duquesne University; Duquesne University; University of Cincinnati kulkarsb@email.uc.edu

Direct developing frogs lack a free-living larval period and hatch from the egg as a juvenile. Even under such extreme rearrangement of ancestral biphasic developmental pattern, development in direct developers is still dependent on thyroid hormone (TH). As vital as TH is to metamorphosis, its hypothalamic regulation plays vital role in deciding the timing of metamorphosis. In particular, corticotropin releasing hormone (CRH) regulates TH production in tadpoles, but in adults, both thyrotropin releasing hormone (TRH) and CRH regulate TH. Because direct developing frogs lack a tadpole stage, it was not clear whether hypothalamic regulation of TH would be tadpole-like or adult-like in embryos. To test this, we compared morphological responses of Eleutherodactylus coqui embryos to CRH and TH treatments. We injected them with 1)60% PBS, 2)CRH, 3)TRH or 4)astressin (CRH receptor antagonist) from Townsend-Stewart (TS) stage 8 and 10 to TS 15. We measured days taken to reach TS 15 and monitored morphological changes, including adult like skin pattern, snout shape, relative hindlimb length and tail resorption. CRH but not TRH significantly accelerated rate of development, whereas astressin-treated animals showed developmental arrest. To confirm the effects of CRH, we examined expression levels of TH receptor (TRbeta) in response to CRH and PBS injections. We found that TRbeta was up-regulated due to CRH but not PBS injections. Our gene expression data confirms results from morphological data that TH production is regulated only by CRH in a tadpole-like manner. We then treated animals with three different doses of TH; 1)ethanol only, 2)2nM, 3)10nM and 4)50nM. We found that 50nM TH significantly increased the rate of development and tail resorption comparable to the results obtained from CRH injections. Thus, our results provide substantial evidence that TH is regulated by CRH in embryos of direct developers. We conclude that despite of evolution of radically different developmental model, the underlying hypothalamic regulation of TH and thus development is well conserved in direct developers.