Jensen Kim B, Watt Fiona M
Keratinocyte Laboratory, Cancer Research UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.
Proc Natl Acad Sci U S A. 2006 Aug 8;103(32):11958-63. doi: 10.1073/pnas.0601886103. Epub 2006 Jul 28.
Considerable progress has been made in characterizing epidermal stem cells by microarray analysis of FACS-selected populations. One limitation of this approach is that the gene expression profiles represent the average of the cell population, potentially masking cellular heterogeneity of functional significance. To overcome this problem, we have performed single-cell expression profiling. We have generated cDNA libraries from single human epidermal cells, designated as stem or transit-amplifying cells on the basis of Delta1 and melanoma-associated chondroitin sulfate proteoglycan expression. Of the 14 putative stem cell markers identified, we selected one, the EGF receptor antagonist leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1), for further study. Lrig1 was expressed in groups of basal cells in human interfollicular epidermis previously identified as enriched for stem cells. Overexpression of Lrig1 decreased keratinocyte proliferation but did not affect the proportion of stem and transit-amplifying cells, as judged by clonal growth characteristics. Down-regulation of Lrig1 using siRNA increased cell-surface EGF receptor levels, enhanced activation of downstream pathways, and stimulated proliferation. Lrig1 acted in part by negatively regulating the Myc promoter. We propose that Lrig1 maintains epidermal stem cells in a quiescent nondividing state, and that Lrig1 down-regulation triggers proliferation.
通过对荧光激活细胞分选术（FACS）筛选的细胞群体进行微阵列分析，在表皮干细胞的特征描述方面已经取得了相当大的进展。这种方法的一个局限性在于基因表达谱代表了细胞群体的平均值，可能掩盖了具有功能意义的细胞异质性。为了克服这个问题，我们进行了单细胞表达谱分析。我们从单个人类表皮细胞中构建了cDNA文库，这些细胞根据Delta1和黑色素瘤相关硫酸软骨素蛋白聚糖的表达被指定为干细胞或过渡增殖细胞。在鉴定出的14个假定的干细胞标志物中，我们选择了一个，即表皮生长因子受体拮抗剂富含亮氨酸重复序列和免疫球蛋白样结构域1（Lrig1），进行进一步研究。Lrig1在先前被鉴定为富含干细胞的人类毛囊间表皮的基底细胞群中表达。通过克隆生长特征判断，Lrig1的过表达降低了角质形成细胞的增殖，但不影响干细胞和过渡增殖细胞的比例。使用小干扰RNA（siRNA）下调Lrig1可增加细胞表面表皮生长因子受体水平，增强下游途径的激活，并刺激增殖。Lrig1部分通过负调控Myc启动子发挥作用。我们提出Lrig1将表皮干细胞维持在静止的非分裂状态，并且Lrig1的下调触发增殖。
