RRC ID 36138
Author Daimon T, Uchibori M, Nakao H, Sezutsu H, Shinoda T.
Title Knockout silkworms reveal a dispensable role for juvenile hormones in holometabolous life cycle.
Journal Proc Natl Acad Sci U S A
Abstract Insect juvenile hormones (JHs) prevent precocious metamorphosis and allow larvae to undergo multiple rounds of status quo molts. However, the roles of JHs during the embryonic and very early larval stages have not been fully understood. We generated and characterized knockout silkworms (Bombyx mori) with null mutations in JH biosynthesis or JH receptor genes using genome-editing tools. We found that embryonic growth and morphogenesis are largely independent of JHs in Bombyx and that, even in the absence of JHs or JH signaling, pupal characters are not formed in first- or second-instar larvae, and precocious metamorphosis is induced after the second instar at the earliest. We also show by mosaic analysis that a pupal specifier gene broad, which is dramatically up-regulated in the late stage of the last larval instar, is essential for pupal commitment in the epidermis. Importantly, the mRNA expression level of broad, which is thought to be repressed by JHs, remained at very low basal levels during the early larval instars of JH-deficient or JH signaling-deficient knockouts. Therefore, our study suggests that the long-accepted paradigm that JHs maintain the juvenile status throughout larval life should be revised because the larval status can be maintained by a JH-independent mechanism in very early larval instars. We propose that the lack of competence for metamorphosis during the early larval stages may result from the absence of an unidentified broad-inducing factor, i.e., a competence factor.
Volume 112(31)
Pages E4226-35
Published 2015-8-4
DOI 10.1073/pnas.1506645112
PII 1506645112
PMID 26195792
PMC PMC4534237
MeSH Alleles Animals Base Sequence Bombyx / embryology Bombyx / genetics* Bombyx / growth & development* Bombyx / ultrastructure Crosses, Genetic Embryo, Nonmammalian / drug effects Embryo, Nonmammalian / embryology Embryonic Development / drug effects Embryonic Development / genetics Endonucleases / metabolism Female Gene Expression Regulation, Developmental / drug effects Gene Knockout Techniques* Gene Targeting Genes, Insect Juvenile Hormones / metabolism* Juvenile Hormones / pharmacology Larva / drug effects Larva / ultrastructure Life Cycle Stages* / drug effects Life Cycle Stages* / genetics Male Molecular Sequence Data Mosaicism Mutation / genetics Phenotype Signal Transduction / drug effects Signal Transduction / genetics Trans-Activators / metabolism
IF 9.412
Times Cited 43
Silkworms m042