Microcarriers as signalling mediators and storage structures
Serendipitously, when we were staining the accessory gland with a range of different cellular dyes, we discovered that the lumen of the gland is filled with neutral lipid-containing structures, which we have called microcarriers. Despite their neutral lipid content, they do not form lipid droplets because they are surrounded by interacting proteins that provide a scaffolding structure. These proteins include Sex Peptide, a small signalling peptide that reprogrammes female behaviours after mating. We have found that microcarriers normally dissipate when they transfer to the female uterus, releasing their contents.
Remarkably, we have discovered that Sex Peptide is required to maintain normal morphology of microcarriers – in its absence, large lipid droplets form in the lumen of the gland. This may be the evolutionarily ancient function of this molecule.
Mammals secrete neutral lipid-containing structures, which can have signalling roles, but equivalent structures in Drosophila have not previously been characterised. Genetic analysis of microcarrier biogenesis should inform our understanding of this novel form of signalling, signal storage and dissipation.
We have recently identified regulators of microcarriers that are misexpressed in specific human diseases, suggesting that defective microcarrier signalling may be involved, a hypothesis that we are testing.
Image Description: Microcarriers in the accessory gland lumen
Confocal image shows lumen of accessory gland expressing a GFP-tagged form of Sex Peptide that labels microcarriers. DAPI stains nuclei of cells in accessory gland lumen. Scale bars = 10 µm. From Wainwright et al., 2020.