14-8 11:45 - 12:00 21-hydroxylase knockout tadpoles survive despite low corticosterone levels Paul, B*; Shewade, LH; Buchholz, DR; University of Cincinnati, Cincinnati, Ohio, USA; SRI International, Menlo Park, California, USA; University of Cincinnati, Cincinnati, Ohio, USA email@example.com https://www.linkedin.com/in/bidishapaul/
Corticosteroids are critical for vertebrate organogenesis. In utero corticosteroid deficiency and/or excess can cause mortality in infants and debilitating diseases in adults. Tadpoles are widely used for studying the mechanism of corticosteroid signaling during development due to conservation of hormonal control of development between humans and frogs. To better understand the role of corticosteroid signaling during development, we created 21-hydroxylase(CYP21A2)(21-OHKO) knockout frogs using CRISPR-Cas9 gene disruption technology. 21-hydroxylase catalyzes corticosteroid biosynthesis from progesterone. CYP21A2 mutations in mammals cause neonatal mortality from corticosteroid deficiency and surviving individuals suffer from infertility. Inhibition of negative feedback to the hypothalamic-pituitary-adrenal(HPA) axis causes overproduction of corticosteroid precursors(e.g. progesterone) resulting in infertility in surviving individuals. We found that 21-OHKO tadpoles have very low plasma glucocorticoid levels, low mRNA expression of glucocorticoid-response gene klf9 and exhibited delayed development. Lack of negative feedback to the HPA axis in mutants resulted in high levels of progesterone and high mRNA expression of crh, acth, star and aldo synthase. Two surprising phenotypes of 21-OHKOs were: 1)survival through metamorphosis unlike mammalian 21-OHKO models which die at birth and 2)similar mineralocorticoid levels as sibling wild-types. Progesterone was found to transactivate glucocorticoid receptor in tail tip culture, which may possibly be sufficient for survival through metamorphosis in vivo. Also, we found higher mRNA expression of aldo synthase which may explain the wild-type mineralocorticoid levels in 21-OHKO tadpoles. Thus, 21-OHKO frogs exhibit impaired HPA negative feedback as in mammals, but compensatory signaling mechanisms likely enable them to survive where mammalian 21-OH mutants die.