Steroid regulated programmed cell death during Drosophila metamorphosis

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• Insect metamorphosis relies on the steroid hormone ecdysone to eliminate larval tissues.
• Programmed cell death (PCD) is crucial for tissue remodeling during development.

Purpose of the Study:

• To investigate the molecular mechanisms by which ecdysone triggers PCD in specific larval tissues.
• To identify the key genes involved in ecdysone-mediated histolysis.

Main Methods:

• Assessing DNA fragmentation and nuclear permeability in dying larval cells using acridine orange staining.
• Inhibiting histolysis via ectopic expression of the baculovirus anti-apoptotic protein p35.
• Analyzing the expression patterns of Drosophila death genes (reaper, head involution defective) and anti-cell death genes (diap2) during metamorphosis.

Main Results:

• Larval midgut and salivary gland histolysis are confirmed as stage-specific, steroid-triggered PCD events.
• Evidence of apoptosis, including DNA fragmentation, was observed in dying larval cells.
• Histolysis was inhibited by p35, indicating a role for caspases.
• Expression of death genes reaper and head involution defective is induced, while anti-cell death gene diap2 is repressed.
• Ecdysone represses diap2 and induces reaper in cultured salivary glands.

Conclusions:

• Ecdysone orchestrates larval tissue death during metamorphosis through precise, stage- and tissue-specific regulation of PCD effector genes.
• The interplay between pro-death (rpr, hid) and anti-death (diap2) genes is critical for developmental tissue remodeling.