Glasø M, Iversen O H, Hovig T
Laboratory for Carcinogenesis and Cell Kinetics, Oslo University, National Hospital, Norway.
Virchows Arch B Cell Pathol Incl Mol Pathol. 1989;56(4):221-35. doi: 10.1007/BF02890021.
The nature and significance of so-called dark keratinocytes in the epidermis during chemical carcinogenesis is still a matter of concern and debate. Based on ultrastructural observations it has been suggested that dark cells most often are shrunken cells. Reports on skin carcinogenesis, however, claim that dark cells are a sign of ongoing tumor promotion and represent those stem cells in the epidermis from which the tumors originate. It is therefore important to find out whether these cells are simply injured and shrunken cells, or vital cells of great importance for carcinogenesis. Dark cells are assumed to be rich in ribosomes. There is evidence, however, that the observed number of dark cells is highly dependent on tissue fixation. In the present ultrastructural study, morphometric methods were used to compare the effects of two different fixation procedures on the amount of cytoplasmic ribosomes in dark cells from both untreated and carcinogen-treated hairless mouse epidermis. The results show that the ultrastructural features of both dark and clear cells vary considerably with different fixation procedures. In acetone-treated controls typical dark cells are only observed when the fixative has a lower osmotic activity than the plasma. With iso-osmolal fixation typical dark cells are not observed. After an abortive two-stage carcinogenesis treatment, in which a single application of 9,10-dimethyl-1,2-benzanthracene (DMBA) in acetone was followed by a single application of 12-O-tetradecanoyl-13-acetate (TPA) in acetone, signs of cell injury could be found after both fixation procedures. With DMBA/TPA and hypo-osmolal fixation the number of dark cells seemed to increase, whereas only signs of cell injury with occurrence of some heavily altered "clear cells" dominated the picture with iso-osmolal fixation. Morphometry showed that both the numerical and the volumetric densities of cytoplasmic ribosomes in basal keratinocytes varied most significantly with the fixation procedure used. The cytoplasmic volumes did not vary in a way that could explain these differences. One might therefore assume that the number of ribosomes depends on the fixative. Large swelling artifacts occurred when a fixative with low osmotic activity was used, leading to compression of neighboring cells. Hence, an increased ribosomal density reported previously in dark cells is probably related to such cell volume artifacts and does not reflect an actually increased quantity of ribosomes.(ABSTRACT TRUNCATED AT 400 WORDS)
在化学致癌过程中，表皮中所谓的暗角质形成细胞的性质和意义仍是一个备受关注和存在争议的问题。基于超微结构观察，有人提出暗细胞最常见的是皱缩细胞。然而，有关皮肤致癌的报告称，暗细胞是肿瘤促进过程持续进行的标志，代表着表皮中肿瘤起源的那些干细胞。因此，弄清楚这些细胞是仅仅受损和皱缩的细胞，还是对致癌作用至关重要的活细胞，这一点很重要。据推测，暗细胞富含核糖体。然而，有证据表明，观察到的暗细胞数量在很大程度上取决于组织固定。在本超微结构研究中，采用形态计量学方法比较了两种不同固定程序对未处理和经致癌物处理的无毛小鼠表皮暗细胞中细胞质核糖体数量的影响。结果表明，暗细胞和亮细胞的超微结构特征因固定程序的不同而有很大差异。在丙酮处理的对照中，只有当固定剂的渗透活性低于血浆时才会观察到典型的暗细胞。采用等渗固定时，未观察到典型的暗细胞。在进行了一次流产的两阶段致癌处理后，即在丙酮中单次涂抹9,10 - 二甲基 - 1,2 - 苯并蒽（DMBA），随后在丙酮中单次涂抹12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯（TPA），两种固定程序后均能发现细胞损伤的迹象。采用DMBA/TPA和低渗固定时，暗细胞数量似乎增加，而在等渗固定时，只有细胞损伤的迹象以及出现一些严重改变的“亮细胞”占主导。形态计量学表明，基底角质形成细胞中细胞质核糖体的数量密度和体积密度随所用固定程序的不同变化最为显著。细胞质体积的变化方式无法解释这些差异。因此，人们可能会认为核糖体的数量取决于固定剂。当使用渗透活性低的固定剂时会出现大的肿胀假象，导致相邻细胞受压。因此，先前报道的暗细胞中核糖体密度增加可能与这种细胞体积假象有关，并不反映核糖体实际数量的增加。（摘要截选至400字）
