Fig. 4. Loss of achi/vis function results in male infertility. (A) Schematic of spermatogenesis; (a) stem cell at apex of testis, (b) zone of mitotic expansion of spermatogonia, (c) primary spermatocytes and meiotic divisions, (d) differentiated sperm. (B-D) Phase contrast image of (B) wild type (arrow indicates bundles of differentiated sperm); (C) Df(2R)achi¹ homozygous testis (note absence of sperm and abundance of undifferentiated primary spermatocytes; arrow); (D) achi^Z3922 vis^Z3922; same phenotype as Df(2R)achi¹; (E) In situ hybridisation with probe recognising the products of both achi and vis. Expression is low/undetectable at the apex (arrow), high in the primary spermatocyte stage and persists into the meiotic divisions.