|Improved derivation efficiency and pluripotency of stem cells from the refractory inbred C57BL/6 mouse strain by small molecules. |
Lin, CJ; Amano, T; Tang, Y; Tian, X
The ability of small molecules to maintain self-renewal and to inhibit differentiation of pluripotent stem cells has been well-demonstrated. Two widely used molecules are PD 98059 (PD), an inhibitor of extracellular-signal-regulated kinase 1 (ERK), and SC1 (Pluripotin), which inhibits the RasGAP and ERK pathways. However, no studies have been conducted to compare their effects on the pluripotency and derivation of embryonic stem (ES) cells from inbred mice C57BL/6, an important mouse strain frequently used to model behavior, cognitive functions, immune system, and metabolic disorders in humans and also the first mouse strain chosen to be sequenced for its entire genome. We found significantly increased derivation efficiency of ES cells from in vivo fertilized embryos (fES) of C57BL/6 with the use of PD (71.4% over the control of 35.3%). Because fES and ES from cloned embryos (ntES) are not distinguishable in transcription or translation profiles, we used ntES cells to compare the effect of small molecules on their in vitro characteristics, in vitro differentiation ability, and the ability to generate full-term ntES-4N pups by tetraploid complementation. NtES cells exhibited typical ES characteristics and up-regulated Sox2 expression in media with either small-molecule. Higher rates of full term ntES-4N pup were generated by the supplementation of PD or SC1. We obtained the highest efficiency of ntES-4N pup generation ever reported from this strain by supplementing ES medium with SC1. Lastly, we compared the pluripotency of fES, ntES and induced pluripotent stem (iPS) cells of C57BL/6 background using the tetraploid complementation assay. A significant increase in implantation sites and the number of full-term pups were obtained when fES, ntES, and iPS cells were cultured with SC1 compared to the control ES medium. In conclusion, supplementing ES cell culture medium with PD and SC1 increases the derivation efficiency and pluripotency, respectively, of stem cells derived from the refractory inbred C57BL/6 strain.
|Acceptance of embryonic stem cells by a wide developmental range of mouse tetraploid embryos. |
Lin, CJ; Amano, T; Zhang, J; Chen, YE; Tian, XC
Biology of reproduction
Tetraploid (4N) complementation assay is regard as the most stringent characterization test for the pluripotency of embryonic stem (ES) cells. The technology can generate mice fully derived from the injected ES cell (ES-4N) with 4N placentas. However, it remains a very inefficient procedure owing to a lack of information on the optimal conditions for ES incorporation into the 4N embryos. In the present study, we injected ES cells from embryos of natural fertilization (fES) and somatic cell nuclear transfer (ntES) into 4N embryos at various stages of development to determine the optimal stage of ES cells integration by comparing the efficiency of full-term ES-4N mouse generation. Our results demonstrate that fES/ntES cells can be incorporated into 4N embryos at 2-cell, 4-cell and blastocyst stages and full-term mice can be generated. Interestingly, ntES cells injected into the 4-cell group resulted in the lowest efficiency (5.6%) compared to the 2-cell (13.8%, P greater than 0.05) and blastocyst (16.7%, P less than 0.05) stages. Because 4N embryos start to form compacted morulae at the 4-cell stage, we investigated whether the lower efficiency at this stage was due to early compaction by injecting ntES cells into artificially de-compacted embryos treated with calcium free medium. Although the treatment changed the embryonic morphology, it did not increase the efficiency of ES-4N mice generation. Immunochemistry of the cytoskeleton displayed microtubule and microfilament polarization at the late 4-cell stage in 4N embryos, which suggests that de-compaction treatment cannot reverse the polarization process. Taken together, we show here that a wide developmental range of 4N embryos can be used for 4N complementation and embryo polarization and compaction may restrict incorporation of ES cells into 4N embryos.