Study On The Pluripoency And The Cell Division Of The Embyonic Germ Stem Cells And Cancer Stem Cells

Pluripotent embryonic stem cells can be expanded seemingly indefinitely in vitro and have the potential to differentiate into any cell type in the body. Thus, they represent an valuable resource for the repair of diseased or damaged tissues. These cells also provide powerful tools for the study of early human embryonic development in vitro. Currently, there are three types of human pluripotent stem cells available for study: embryonic stem cells (ESCs), embryonic germ cells (EGCs), and induced pluripotent stem cells (iPS). ESCs are derived from the inner cell mass of pre-implantation blastocysts, whereas embryonic germ cells (EGCs) are derived from the primordial germ cells (PGCs) of embryos in later stages of development. Human iPS cell lines are derived from somatic cells that have been"reprogrammed"by the introduction of key stem cell identity factors such as OCT4, SOX2, NANOG, and others。Research on human ESCs has caught public attention, and many studies have begun to elucidate the mechanisms of establishment and differentiation. iPS, which only emerged in 2007 have also served to stimulate interest in stem cell biology. However, only a handful of laboratories currently perform research on hEGCs. Germline cells have some key differences from ESCs and iPS cells, as they are responsible for transmitting genetic information from generation to generation. Understanding the establishment and differentiation of hEGCs in vitro will be an important step towards successful germline gene therapies, thus hEGCs deserve more study.Unlike ESCs and iPS, hEGCs expand very slowly in culture. It is difficult to generate large quantities of undifferentiated hEGCs, which limits further basic and clinical applications of these cells. We have investigated hEGC cell division as a potential step at which hEGC proliferation might be controlled in the lab. Cell division can occur in one of two patterns, symmetric or asymmetric. Several studies have indicated that hEGCs might undergo asymmetric division.Numb has been shown to play a determinant role in generating asymmetric cell divisions by negatively regulating Notch1 signaling. In order to test our hypothesis that Numb is involved in controlling hEGC division, we first investigated the expression of Numb in hPGCs in vivo. we confirmed that hPGCs and cultured hEGCs both express Numb at high levels. In the 24 h culture, hEGCs displayed a crescent of Numb staining, similar to other cells that undergo asymmetric division.We next investigated whether cell proliferation was affected when Numb function is suppressed. To this end, we used a Dox-induced siRNA system with the lentiviral vector pLKO-Tet-On-TRE U6-puro sh Numb (Tet-on Numb shRNA). These results show that hEGC cultures could be converted from poorly proliferating to vigorously proliferating cells by Numb RNAi, suggesting that Numb expression is involved in hEGC division.These results indicate that the Numb/Notch1 pathway is activated in, and plays a role in mediating, hEGC division. This, in turn, suggests that Numb might be responsible for maintaining asymmetric cell division potential by negatively regulating Notch1 protein levels.SiN-hEGCs expressed characteristic markers of hEG cells and were able to differentiate into cell types of all three primary germ layers. The results presented here suggest that specifically targeted inhibition of Numb expression could be used to facilitate hEGC culture in vitro. These encouraging findings provide a starting point for basic and clinical study of hEGCs.Octamer 4 (Oct4), a member of the POU family of transcription factors, plays a key role in the maintenance of pluripotency and proliferation potential of embryonic stem cells. Cancer stem cell–like cells (CSCLC) are reported to be a minor population in tumors or even in tumor cell lines which also express Oct4.The role of Oct4 in CSCLCs still remains to be defined. In our study, we show that, in vitro, almost all murine Lewis lung carcinoma 3LL cells and human breast cancer MCF7 cells express Oct4 at high levels. This expression of Oct4 is successfully reduced by small interfering RNA, which eventually results in cell apoptosis. The signal pathway Oct4/Tcl1/Akt1 has been observed to be involved in this event. The repression of Oct4 reduces Tcl1 expression and further downregulates the level of p-Ser.473-Akt1. In vivo, only 5% of tumor cells were detected to express Oct4 in established 3LL and MCF7 tumor models, respectively. Small interfering RNA against Oct4 successfully decreases the CSCLCs and markedly inhibits tumor growth. In summary, we show that Oct4 might maintain the survival of CSCLCs partly through Oct4/Tcl1/ Akt1 by inhibiting apoptosis.In summary, we show here for the first time that reduction of Oct4 expression in CSCLCs induces apoptosis and the inhibition of tumor growth partly through the Oct4/Tcl1/Akt1 pathway. The strategy described here strongly suggests that specific targeted inhibition of stem cell signaling pathways could be applied to cancer therapy.