Regulation of Metamorphosis in Holometabolous Insects - PubMed
4 hours ago
- #holometabolous insects
- #gene regulation
- #metamorphosis
- Holometabolous insects' metamorphosis is regulated by three genes: chinmo, broad, and E93, corresponding to larval, pupal, and adult stages.
- A temporal endocrine landscape involving ecdysteroids, juvenile hormone (JH), and myoglianin controls life stage transitions.
- Chinmo suppresses broad and E93, acting as an anti-metamorphic gene.
- JH target gene Krüppel-homolog 1 (Kr-h1) also suppresses metamorphosis, with JH's role varying by larval stage.
- Early larval molts are JH-independent, while later ones require JH to maintain larval molting and suppress E93 until a size threshold is met.
- Myoglianin and/or ecdysteroids induce broad expression, and declining JH levels can stimulate E93.
- Entry to metamorphosis is mediated by either E93 (Tribolium) or broad (Drosophila), depending on JH necessity.
- Inhibitory interactions between broad and E93, along with JH's return in the prepupa, ensure pupa formation precedes adult differentiation.
- In hemimetabolous insects, Chinmo and JH (via Kr-h1) maintain the nymphal stage and suppress E93 and adult differentiation.
- Broad and chinmo collaborate in nymphal growth, with chinmo supporting isomorphic growth and broad supporting positive allometric growth.
- Mutual inhibition between these transcription factors was a key evolutionary innovation, enabling imaginal primordia expansion in larvae before pupal morphogenesis.