THE STRUCTURE AND FORMATION OF PROTEIN GRANULES IN THE FAT BODY OF AN INSECT

Area of Science:

• Cell Biology
• Developmental Biology
• Insect Biochemistry

Background:

• The fat body in insect larvae plays a crucial role in nutrient storage and metabolism.
• Protein storage granules are essential for developmental transitions, such as pupation.
• Understanding the biogenesis of these storage granules is key to comprehending insect metamorphosis.

Purpose of the Study:

• To investigate the cellular mechanisms and origins of protein granule formation in the fat body of Calpodes ethlius larvae.
• To characterize the distinct types of protein granules and their formation pathways.
• To explore the role of cellular organelles, like the Golgi complex and endoplasmic reticulum (ER), in granule synthesis.

Main Methods:

• Light and electron microscopy to observe cellular structures and granule formation.
• Analysis of temporal events preceding pupation (30-35 hours and 10 hours before).
• Identification of granule origins from Golgi vesicles and isolated ER regions.

Main Results:

• Two types of protein granules identified: those originating from Golgi vesicles and those from isolated ER regions.
• Golgi-derived granules increase in size through microvesicle incorporation and coalescence.
• ER-derived granules form via isolation bodies that coalesce, potentially storing both protein and RNA, and resemble cytolysomes when inner membranes are lost.

Conclusions:

• Protein granule formation in Calpodes ethlius fat body involves distinct pathways originating from the Golgi complex and endoplasmic reticulum.
• The process highlights the dynamic nature of cellular organelles during insect metamorphosis.
• Membrane-bound isolation of cellular components, including ER and mitochondria, may be a general mechanism for sequestration or lysis.