Amyloid Fibrils of the s36 Protein Modulate the Morphogenesis of Drosophila melanogaster Eggshell.

Drosophila melanogaster is the oldest classic model object in developmental genetics. It may seem that various structures of the fruit fly at all developmental stages have been well studied and described. However, recently we have shown that some specialized structures of the D. melanogaster eggshell contain an amyloid fibril network. Here, we demonstrate that this amyloid network is formed by the chorionic protein s36. The s36 protein colocalizes with the amyloid-specific dyes Congo Red and Thioflavin S in the micropyle, dorsal appendages, and pillars. The fibrils of s36 obtained from the eggs demonstrate amyloid properties. In the context of the CG33223 gene deletion, the s36 protein is produced but is not detected in the eggshell. The absence of amyloid fibrils of s36 in the eggshell disrupts the endochorion morphology and blocks the development of the micropyle, dorsal appendages, and pillars, leading to sterility. Our data show for the first time that amyloid fibrils are essential for morphogenesis modulation. We suggest that attachment of follicle cells to the s36 extracellular fibrils triggers signaling to enable subsequent cellular divisions needed for building the specialized eggshell structures.