Ramirez R D, Wright W E, Shay J W, Taylor R S
Department of Cell Biology, The University of Texas Southwestern Medical Center at Dallas, 75235-9069, USA.
J Invest Dermatol. 1997 Jan;108(1):113-7. doi: 10.1111/1523-1747.ep12285654.
Telomerase is a ribonucleoprotein enzyme capable of adding hexanucleotide repeats onto the ends of linear chromosomal DNA. Whereas normal somatic cells with a limited replicative capacity fail to express telomerase activity, most immortal eukaryotic cells do. Cells of renewal tissues (e.g., skin, intestine, blood) require an extensive proliferative capacity. Some cells in such renewal tissues also express telomerase activity, most likely to prevent rapid erosion of their telomeres during cell proliferation. In this study, we measured the levels of telomerase activity in dissected compartments of the human hair follicle: hair shaft, gland-containing fragment, upper intermediate fragment (where it is thought undifferentiated stem cells reside), lower intermediate fragment, and in the bulb-containing fragment (an area with high mitotic activity containing a more differentiated pool of keratinocytes). In anagen follicles, high levels of telomerase activity were found almost exclusively in the bulb-containing fragment of the follicles, with low levels of telomerase in the bulge area (intermediate fragments) and gland-containing fragment. In comparison, catagen follicles had low levels of telomerase activity in the bulb-containing fragments as well as in other compartments. Such observations indicate that, in anagen hair follicles, the fragments containing cells actively dividing (e.g., transient amplifying cells) express telomerase activity, whereas fragments containing cells with low mitotic activity, for example, quiescent stem cells, express low levels of telomerase activity.
端粒酶是一种核糖核蛋白酶，能够在线性染色体DNA末端添加六核苷酸重复序列。具有有限复制能力的正常体细胞无法表达端粒酶活性，而大多数永生化真核细胞则可以。更新组织（如皮肤、肠道、血液）的细胞需要广泛的增殖能力。此类更新组织中的一些细胞也表达端粒酶活性，最有可能是为了防止其端粒在细胞增殖过程中快速缩短。在本研究中，我们测量了人毛囊不同解剖部分的端粒酶活性水平：毛干、含腺体片段、上中间片段（一般认为未分化干细胞所在部位）、下中间片段以及含毛囊球片段（有高有丝分裂活性的区域，含有分化程度更高的角质形成细胞池）。在生长期毛囊中，几乎仅在毛囊的含毛囊球片段中发现高水平的端粒酶活性，而在隆突区（中间片段）和含腺体片段中端粒酶水平较低。相比之下，退行期毛囊在含毛囊球片段以及其他部分的端粒酶活性都较低。这些观察结果表明，在生长期毛囊中，含有活跃分裂细胞（如短暂增殖细胞）的片段表达端粒酶活性，而含有低有丝分裂活性细胞（如静止干细胞）的片段表达低水平的端粒酶活性。
