A mutant affecting the crystal cells inDrosophila melanogaster

Area of Science:

• Developmental Biology
• Cell Biology
• Genetics

Background:

• Drosophila melanogaster larvae possess crystal cells, a type of hemocyte containing paracrystalline inclusions.
• Mutant larvae exhibiting black cells (Bc) show melanized cells in hemolymph and lymph glands.
• The genetic basis and cellular origin of these black cells were previously unclear.

Purpose of the Study:

• To investigate the identity and origin of black cells in Bc mutant Drosophila melanogaster larvae.
• To elucidate the role of the Bc+ gene in crystal cell development and melanization.
• To understand the mechanism of phenol oxidase activity and substrate storage in Drosophila hemocytes.

Main Methods:

• Larval and embryonic development observation in wild-type, heterozygous (Bc+/Bc), and homozygous mutant (Bc/Bc) Drosophila.
• Phenotypic analysis of black cell distribution and comparison with experimentally induced melanization.
• Enzyme activity assays for phenol oxidase in cell-free larval extracts.

Main Results:

• Black cells in Bc mutants are identified as a dysmorphic form of crystal cells; Bc larvae lack functional crystal cells.
• The distribution of black cells mimics experimentally melanized crystal cells, indicating a phenocopy.
• Phenol oxidase activity is significantly reduced in heterozygotes and undetectable in homozygotes, correlating with crystal cell integrity.

Conclusions:

• The Bc+ gene product is essential for maintaining the structural integrity of paracrystalline inclusions within crystal cells.
• Loss of Bc+ function leads to uncontrolled melanization due to substrate and enzyme interaction.
• Crystal cells are confirmed as the primary storage site for phenolic substrates and the source of larval hemolymph phenol oxidase.