Preserving Hard and Delicate Structures: Sample Preparation for Histology and Electron Microscopy of Hatching Freshwater Sponge Gemmules

Many objects of developmental biology are structurally heterogeneous, being composed of diverse tissues that present unique challenges for sample preparation and microscopic analysis. Adapting protocols to these structural peculiarities is, therefore, a crucial step for investigations in this field. A prime example is the hatching gemmule of the freshwater sponge (Linnaeus, 1759), which comprises a central cell mass surrounded by a rigid outer shell with silicious spicules, and a delicate migratory front composed of cells leaving the gemmule and spreading along the substrate. The objective of our study was to optimize sample preparation protocols to investigate the migratory behavior of cells during early development using histology, scanning electron microscopy, and transmission electron microscopy.