In the cystoblast, however, the original fusome does not elongate toward the plug as fusome and plug fuse. Thus, it could not be determined if the original fusome moves toward the plug, or if the plug and ring canal move towards the original fusome. Because it is formed from two smaller fusomes, the fused fusome has also been called a polyfusome . After fusion, the cell that lacks a fusome at cytokinesis contains less fusomal material than its sister cell and, apparently, it does not accumulate more during the rest of interphase. Fusion takes place as the plugs move towards the central fusome and as fusomal material accumulates in the gaps between them.
All plugs fuse before the next round of mitosis begins.
Thus, 16-cell cysts whose fusomes are in the process of fusing are located in region 2a of the germarium. It is likely that some fusomal material is newly synthesized or assembled as the cyst grows, since fusomes in 16-cell cysts are much bigger than cystoblast fusomes. Based on this observation, the cell with the most fusomal material in a 16-cell cyst is probably the same cell that retained the fusome at cytokinesis in the cystoblast. Thus, the initial asymmetry of the fusome is maintained throughout cyst formation. Fusome morphogenesis was examined in two mutants in which cyst polarity appears to be disrupted.