Effects of FSH, interstitial cells, and granulosa cells on follicular growth in the three-dimensional follicle culture. Follicles cultured in collagen gel (a) without both FSH and interstitial cells, (b) with FSH and without interstitial cells, (c) with both FSH and interstitial cells, and (d) with both FSH and granulosa cells for 5 days. Arrows in (c) show the follicular antrum-like cavity. The arrowheads in (c) show a cell layer formed in the outermost part of the follicle during culture. O, oocyte; G, granulosa cells. Scale bars = 25 μm.