Role of the Terpenoid Hormone Methyl Farnesoate and Receptor Ultraspiracle (RXR) in Generation of the Epidermal Cuticular Barrier in Drosophila Melanogaster

Program: Abstracts - Orals, Poster Previews, and Posters
Session: SUN 203-235-Steroid Hormone Actions, Biosynthesis and Metabolism (posters)
Bench to Bedside
Sunday, April 3, 2016: 1:15 PM-3:15 PM
Exhibit/Poster Hall (BCEC)

Poster Board SUN 235
Davy Jones1, Anna Niewiadomska-Cimicka2, Agnes Sapa3, Cameron Colvard4, Rebecca Spokony*5 and Grace Jones1
1University of Kentucky, Lexington, KY, 2IGBMC, 3Wroclaw Medical University, Wroclaw, Poland, 4University of Kentucky, 5Baruch College, CUNY, New York
A highly conserved morphogenetic principle in vertebrates and invertebrates is the epidermal generation of a surface barrier separating the internal and external environments.1 In humans, the inert barrier is derived from the epidermis as a continuously generated layer of dead, cross-linked skin cells, while in insects the epidermis secretes and maintains a cuticle of cross-linked proteins and chitin.  In Drosophila melanogaster, the final act of larval epidermal differentiation is the formation of the puparial cuticular barrier and subsequent apolytic separation of the epidermal sheet.  This cuticular barrier is considered essential to protect the subsequent fragile pupal stage from dehydration and pathogens. The morphogenesis of the puparial cuticle is hypothesized to be dependent on an axis of a terpernoid hormone (methyl farnesoate, MF) and nuclear receptor ultraspiracle (USP, = vertebrate RXR).

Our previous studies using transgenic usp expressed under the control of the natural usp promoter in animals that were otherwise null for usp found that mutation to the ligand pocket (Q288A L366A), strongly reduced MF binding and blocked generation of the puparial cuticle.2,3  Presently, our microscopy studies determined that the epidermal sheet also prematurely separates from the cuticle, and the subsequent pupal stage animals rapidly dehydrate.  Microarray expression analysis indicated that the majority of the most misexpressed (underexpressed) genes at the outset of processes leading to puparium formation are genes encoding cuticular structural proteins.  qPCR analysis on isolated integument from that developmental stage confirmed the distinct misexpression of these genes. Expression analysis also confirmed that potential direct targets of MF/USP signaling (DHR3 (= ROR) and grainyhead) are misexpressed in the mutant QLUSP integument several hours before control animals pupariate.  Chromatin immunoprecipitation, here validated by qPCR, confirmed that at this developmental period USP occupies a binding site in the DHR3 first intron. 

Our results support the existence of a ligand/RXR (MF/USP) regulatory network for generation of a particular developmentally-timed and uniquely comprised epidermal cuticular barrier.

1Mace KA, Pearson JC, McGinnis W. Science. (2005)308: 381-5

2Jones D, Jones G, Teal PE. (2013) Gen Comp Endocrinol. 194: 326-335

3Jones G, Teal P, Henrich VC, Krzywonos A, Sapa A, Wozniak M, Smolka J, Jones D. (2013) Gen Comp Endocrinol.182:73-82

Nothing to Disclose: DJ, AN, AS, CC, RS, GJ

*Please take note of The Endocrine Society's News Embargo Policy at https://www.endocrine.org/news-room/endo-annual-meeting/pr-resources-for-endo

Sources of Research Support: National Science Foundation 1052142 (GJ)