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The molecular physiology and the evolution of a new pathway promoting developmental stability

Final Report Summary - FLY-PHY (The molecular physiology and the evolution of a new pathway promoting developmental stability)

Developmental stability is the ability of an organism to buffer traits against environmental or intrinsic perturbations occurring during development. The processes leading to developmental stability have been particularly well studied in arthropods. These processes can involve physiological, temporal or behavioral adjustments. For instance, upon uncoordinated growth of the Drosophila larval imaginal discs (the precursors of adult appendages), which would otherwise lead to disproportionate adults, the onset of metamorphosis is transiently inhibited, allowing more time for disc growth harmonization. How exactly this exquisite coordination between growth and developmental timing is achieved is not completely understood. Recently, others and us have identified a fly-specific insulin/relaxin peptide named Drosophila insulin-like peptide 8 (Dilp8) that responds to uncoordinated tissue growth and delays the onset of metamorphosis by inhibiting, via an unknown mechanism, the biosynthesis of the major insect molting hormone, Ecdysone. Loss of dilp8 increases intra-individual asymmetry and yields individuals with a greater than normal range of size variation and time of maturation. Thus, Dilp8 is a central player in the communication system that mediates plasticity to promote developmental stability in Drosophila. The objectives of this project were to identify the mechanism of action of Dilp8 and to understand how this new peptide became incorporated into a conserved tissue-stress sensing pathway. To reach these objectives, we planned to identify the target tissue/s that mediate Dilp8 function(s), the signaling pathway that it acts through, and determine when it originated and became responsive to abnormal growth during dipteran evolution. Here, we have identified the orphan Leucine-Rich Repeat-containing G protein coupled receptor (Lgr3) as a critical player in the Dilp8 developmental stability pathway. Lgr3 is required in a subpopulation of central nervous system interneurons to relay the peripheral Dilp8 signal to the neuroendocrine centers that control the timing of pupariation. We have also defined a new temporally and spatially distinct role for the Dilp8-Lgr3 pathway in controlling cuticle remodeling at pupariation. On a second front, we furthered our understanding of the evolution of the dilp8 gene by using RNASeq to identify ilp8-like genes in divergent dipterans and by studying their ability to respond to abnormal tissue growth and delay development. This grant has facilitated the establishment of an independent group led by the grantee at his host institution. The group has grown to host 12 additional members, including 2 Associate Researchers, 4 PhD students, 1 long-term visiting PhD student, 2 MSc students, 1 Lab Manager, and 2 Research Fellows. The group has been awarded competitive national and international grants. Five MSc theses have successfully been defended. Two PhD students will defend their theses early next year. One manuscript was published and between three and four manuscripts and one patent application are predicted to originate from this work within the next year. In summary, significant progress has been made not only in the scientific aspects of the project but also in the career development of the grantee.