Self-renewal pattern-associated genes and their role in adult stem cell functions

Abstract

Molecular markers for adult stem cells (ASCs) are highly demanded for research and clinical applications. The development of specific molecular markers for ASCs has been difficult mainly due to the technical barriers in the identification and isolation of rare ASCs. Previously, reported transcriptional profiling studies for defining molecular features of ASCs were compromised by the use of impure ASC preparations. Thesis for this research was that the study of asymmetric self-renewal, a defining property of ASCs, might provide key clues to understanding ASC function and lead to discovery of novel molecular markers for ASCs. Fifty two self-renewal pattern associated (SRPA) genes were identified by cDNA microarray analysis with cell culture models whose self-renewal pattern could be reversibly regulated, instead of using heterogeneous ASC-enriched populations. From evaluation of whole genome transcript levels to expand the SRPA gene pool, 543 SRPA genes were discovered. Both microarray studies showed that asymmetric self-renewal associated (ASRA) genes were highly represented in ASC-enriched populations but not in embryonic stem cells. The SRPA gene expression signature successfully distinguished isolated ASC-enriched populations from non-stem cell populations by principal component analysis (PCA).

(cont.) The SRPA gene signature clustered and classified putative epidermal stem cell-enriched populations better than reported stemness gene signatures in PCA. Therefore, gene microarray analyses for studying self-renewal pattern per se confirmed for the first time that asymmetric self-renewal is an essential molecular feature of ASCs in vivo. Chromosome mapping of the SRPA genes identified two SRPA chromosome gene cluster regions. One chromosome cluster contained primarily ASRA genes, whereas the other contained primarily symmetric self-renewal associated (SSRA) genes. These two SRPA chromosome cluster regions are frequently rearranged or deleted in particular human cancers. Functional and expression analysis of several selected ASRA and SSRA gene-encoded proteins implicated them in control of asymmetric self-renewal and non-random chromosome co-segregation, respectively. Moreover, one plasma membrane bound ASRA protein, CXCR6, had properties of one of the most specific molecular markers for ASCs described to date. In conclusion, this research strongly supported the precept that asymmetric self-renewal is a unique molecular feature for understanding ASCs, their relation to cancer, their unique function, and for their eventual exclusive identification.