Hemocytes and hemocytopoiesis in Silkworms

Area of Science:

• * Entomology
• * Cell Biology
• * Developmental Biology

Background:

• * Silkworms (Bombyx mori and Antheraea pernyi) possess five circulating hemocyte types: prophemocytes, plasmatocytes, granulocytes, spherule cells, and oenocytoids.
• * Plasmatocytes are considered pluripotent, differentiating into other hemocyte types, though they lack phagocytic activity in Antheraea.
• * The functions of spherule cells remain unclear, while oenocytoids exhibit phenoloxidase activity involved in phenol metabolism.

Purpose of the Study:

• * To review the ultrastructure, cytochemistry, and physiology of silkworm hemocytes and peri-imaginal-wing organs.
• * To investigate the hemocytopoietic role of meso- and metathoracic peri-imaginal-wing organs in silkworms.
• * To understand the contribution of these organs to maintaining hemocyte populations during post-embryonic development.

Main Methods:

• * Morphological classification of hemocytes.
• * Ablation experiments to assess the function of peri-imaginal-wing organs.
• * Analysis of hemocytograms and mitotic activity in hemocytes and organs.

Main Results:

• * Ablation of peri-imaginal-wing organs disrupts hemocytogram maintenance, indicating their essential hemocytopoietic function.
• * These organs contain compact and reticulate islets, with prohemocytes being the predominant cell type in hemocytopoietic organs.
• * Mitotic divisions and hemocyte differentiation within these organs show cyclic changes parallel to the molting cycle.

Conclusions:

• * Peri-imaginal-wing organs are critical sites for hemocytopoiesis in silkworms, supplementing the mitotic activity of circulating hemocytes.
• * Prohemocytes within these organs are key stem cells for hemocyte production.
• * Hemocyte production and differentiation are tightly regulated and synchronized with the silkworm molting cycle.