During animal gametogenesis, germ cells are connected by intercellular bridges that allow the flow of cytoplasm – and signals – between the cells. In Drosophila, the bridges are called ring canals (RCs) and are built from cleavage furrows that fail to complete cytokinesis; another specialised organelle called the fusome provides further interconnectivity, threading through the RCs. Functions for RCs and the fusome in fertility have been demonstrated in female flies, but much less is known about the role of these intercellular connections in male gametogenesis. Now, Lynn Cooley and colleagues address this issue using live imaging, genetics and electron microscopy. They first find that RCs permit movement of photoactivated GFP in mitotic spermatogonial cells. Although some endogenously tagged proteins were also observed transiting between cells, others did not (including a protein known to transit between cells in the ovary), showing that free diffusion is limited to certain proteins. Protein movement also occurs in meiotic and post-meiotic cysts and in elongated spermatids. Where the structure of the fusome is disrupted with Spectrin RNAi, testes morphology is normal, RCs still form (though some are malformed), fertility is only negligibly affected and photoactivated GFP can still diffuse between cells (albeit at a slightly quicker rate). Thus, although male germline RCs provide cytoplasmic interconnectivity, an intact fusome appears to have little or no functional role, in stark contrast to the female germline.
