Expression of SciSoxE , SciSoxF1 , SciSoxF2 , SciSox6 , and SciSox7 . SciSoxE is expressed in choanocytes (ch) (A, B) and a fraction of mesohyle cells, particularly prominent in the apical (oscular) part (A). The expression is undetectable in the oocytes and accessory cells (ac) (B). SciSoxF1 expression is limited to choanocytes (C, D) and accessory cells (D), and absent in the embryos (D). SciSoxF2 is weakly expressed in the choanocytes (E) and strongly in large spindle shape cells surrounding the osculum (E, magnified on F). SciSox6 is strongly expressed in choanocytes (ch), pinacocytes (pin), and a variety of mesohyle cells, especially those in the apical part (G, H), but not in embryos (H). SciSox7 is expressed in choanocytes (I, J) and strongly expressed in the oocytes (J). Top row: oscular parts of young sponges. Bottom row: B - plastic section of sponge containing oocytes. D- thick slice of sponge containing embryos during pre-inversion. F- magnification of the tip of the osculum. H- Plastic sections of sponge containing post-inversion stage embryo. J - thick slice of sponge containing small oocytes.