Genetic Analysis of the Role of the Reprogramming Gene LIN-28 in Human Embryonic Stem Cells

Abstract

LIN-28 is a gene recently shown to be involved in the conversion of somatic cells to induced pluripotent stem cells. We have previously shown that LIN-28 is highly expressed in human embryonic stem cells (HESCs); however, its role in these cells has not been investigated. We now show that, like OCT4, SOX2, and NANOG, LIN-28 is downregulated during differentiation of HESCs into embryoid bodies. In addition, we investigate the role of LIN-28 in HESCs by manipulation of its expression levels. LIN-28 overexpression impairs the ability of cells to grow at clonal densities, due to increased differentiation and decreased cell division. Analysis of cell differentiation under these conditions revealed that it is mostly towards the extraembryonic endoderm lineage. Moreover, we show that, during early mouse development, high levels of Lin-28 are also observed in the extraembryonic endoderm, and therefore it seems that, both in vitro and in vivo, high levels of LIN-28 may specify an extraembryonic endoderm fate. However, LIN-28 seems dispensable for selfrenewal of HESCs; its downregulation neither impairs HESC proliferation nor leads to their differentiation. Thus, LIN-28 does not seem to be involved in the self-renewal of HESCs, but rather seems to be involved in their decision to switch from self-renewal to differentiation.

Lin-28 Homologue A (LIN28A) Promotes Cell Cycle Progression via Regulation of Cyclin-dependent Kinase 2 (CDK2), Cyclin D1 (CCND1), and Cell Division Cycle 25 Homolog A (CDC25A) Expression in Cancer

“…This finding has been successfully phenocopied in a transgenic mouse model with an inducible LIN28A gene (21). Increasing evidence suggests that LIN28 may also be a master regulator controlling the pluripotency of embryonic stem (ES) 4 cells (22)(23)(24)(25). LIN28A, together with OCT4, SOX2, and NANOG (the "reprogramming factors"), can reprogram somatic cells to induced pluripotent stem cells (26).…”

“…It has been well demonstrated that LIN28A promotes ES cell proliferation (22,23,28) via regulation of the G 2 /M transition of the cell cycle (23). Recent studies in cancer also found that knocking down LIN28A expression in cancer cell lines can remarkably reduce cancer cell viability and inhibit cell growth in vitro (42,45,62).…”

Pluripotency factors Lin28 and Oct4 identify a sub-population of stem cell-like cells in ovarian cancer

“…In human tissues, Lin28 expression has been detected in normal ovarian surface epithelium (Viswanathan et al, 2009) as well as in mature oocytes (Assou et al, 2009). Lin28 expression is high in human and mouse embryonic stem (ES) cells, and decreases dramatically during ES cell differentiation (Richard et al, 2004;Darr and Benvenisty, 2008). The biological importance of Lin28 is further underscored by its ability to facilitate the reprograming of human somatic cells to induced pluripotent stem cells (Yu et al, 2007).…”

The role of Trim25 in development, disease and RNA metabolism

“…In metazoans Lin28a is abundantly expressed in the early stages of embryonic development, during which it inhibits the biogenesis of miRNAs from the let-7 family. Lin28a expression is gradually restricted with development, which allows de-repression of let-7 production in more developed and differentiated cells [36][37][38][39][40]. The main mechanism by which Lin28a inhibits let-7 biogenesis is based on its interaction with the conserved terminal loop [41] of pre-let-7 [42][43][44].…”