Toyoshima K, Leighton J
Cancer Res. 1975 Jul;35(7):1873-9.
The Nara Bladder Tumor No. 2 cell line, established from a urinary bladder carcinoma in the Wistar rat, formed keratinizing cells and multicellular pearls in meniscus gradient culture when fed with a medium of 15 or 30% fetal calf serum in Eagle's minimal essential medium. Confluent monolayer cultures were first prepared with the tubes in conventional horizontal position. When cultures were then changed to a vertical position, stratification, piling up, and aggregation of cells were observed in a few days at the aerobic end of the gradient. Keratinization appeared 1 week after the tubes were placed in vertical position. Squamous differentiation proceeded to the formation of keratin pearls, a phenomenon never observed so distinctly and in such abundance in horizontal culture. Supplements of vitamin A, as low as 1 IU/ml, added to the medium did not inhibit piling up or aggregation but did prevent keratinization. Inhibition of keratinization by vitamin A was reversible. After vitamin A was removed from the medium, the cells in the aggregates progressed to keratinization.
奈良膀胱肿瘤2号细胞系源自Wistar大鼠的膀胱癌，在伊格尔最低必需培养基中加入15%或30%胎牛血清培养时，于半月板梯度培养中形成角质化细胞和多细胞珠。首先将培养管置于传统水平位置制备汇合单层培养物。当培养物随后改为垂直位置时，在梯度的需氧端几天后观察到细胞分层、堆积和聚集。在培养管置于垂直位置1周后出现角质化。鳞状分化进展为角质珠的形成，这一现象在水平培养中从未如此明显和大量地观察到。向培养基中添加低至1 IU/ml的维生素A不会抑制堆积或聚集，但会阻止角质化。维生素A对角质化的抑制是可逆的。从培养基中去除维生素A后，聚集体中的细胞进展为角质化。
