Expression of lysozyme throughout the life history of the house fly, Musca domestica L.

From egg to adult, all life history stages of house flies associate with septic environments

teeming with bacteria. House fly lysozyme was first identified in the larval midgut, where it is used

for digestion of microbe-rich meals because of its broad-spectrum activity against gram-positive and

gram-negative bacteria as well as fungi. This study aimed to determine the temporal expression of

lysozyme in the life history of house flies (from egg through adults) on both the mRNA and protein

level, and to determine the tissue-specific expression of lysozyme in adult flies induced by feeding

Staphylococcus aureus. From 30-min postoviposition through adulthood, all life history stages of the

house fly express lysozyme on the mRNA level. In adult flies, lysozyme is expressed both locally in the

alimentary canal and systemically in the fat body. Interestingly, we found that during the normal life

history of flies, lysozyme protein was only detected in larval stages and older adults, likely because

of ingestion of immune-stimulating levels of bacteria, not experienced during egg, pupa, and teneral

adult stages. Constitutive expression on the mRNA level implies that this effector is a primary defense

molecule in all stages of the house fly life history and that a mechanism for posttranscriptional control

of mature lysozyme enzyme expression may be present. Lysozyme-active enzyme primarily serves

both a digestive and defensive function in larval and adult flies, and may be a key player in the ability

of Musca domestica L. to thrive in microbe-rich environments.