A pinboard by
Ryan Taylor

I am a second year PhD student working at the Roslin Institute

I work with rat stem cells


Manipulating the gene network of rat stem cells to ensure they are passed onto future generation

Rats are one of the many animals used by scientists to help them with their scientific research. They are a great model for human diseases and disorders such as cardiovascular disease, due to their surprisingly similar biochemical and immunological responses. In 2008, a method was successfully carried out to isolate and grow stem cells from rat embryos in a laboratory environment. This success opened up an even greater number of potential scientific avenues to explore. However, it seemed that by growing these rat embryonic stem cells (rESCs) outside of their normal environment, they did not respond as would be expected. For instance, introducing lab-grown rESCs to developing rat embryos gave rise to healthy offspring containing DNA from both parents and the lab-grown rESCs. However, in some cases after these rats went on to produce offspring themselves, there was no indication of lab-grown rESCs in the population, meaning there was no evidence of any DNA or protein which had come from lab-grown rESCs. This ability to pass on lab-grown rESCs into the next generations seems to vary depending on what species of rat the rESCs came from, as well as what species of rat produced the embryo the rESCs are being introduced into. Stem cells have the capability to become almost any cell in the body, given the right stimulus of signals. So perhaps by growing these cells in the lab, it desensitizes them to the natural signals in the developing embryos telling them to be passed on to future generation? The aim of my work is to identify whether it is possible to improve the number of stem cells which are able to make it into future generations by turning them into the cells which will become reproductive cells. I’m attempting this by increasing the expression of certain genes which are thought to be important for making reproductive cells. This follows on from what has been previously done in mice. By influencing the gene expression of lab-grown rESCs, I am hoping to push the cells into becoming a cell type known as Primoridal Germ Cells or PGCs. These cells can give rise to both male and female reproductive cells, which then pass on the instructions for future generations. It is hoped that by pushing these cells into PGCs, we can improve the efficiency of rESCs being passed on to the next generation, potentially opening up potential solutions to infertility issues in humans and further our knowledge into how traits are passed onto the next generation.


NANOG alone induces germ cells in primed epiblast in vitro by activation of enhancers

Abstract: Nanog, a core pluripotency factor in the inner cell mass of blastocysts, is also expressed in unipotent primordial germ cells (PGCs) in mice1, where its precise role is yet unclear2, 3, 4. We investigated this in an in vitro model, in which naive pluripotent embryonic stem (ES) cells cultured in basic fibroblast growth factor (bFGF) and activin A develop as epiblast-like cells (EpiLCs) and gain competence for a PGC-like fate5. Consequently, bone morphogenetic protein 4 (BMP4), or ectopic expression of key germline transcription factors Prdm1, Prdm14 and Tfap2c, directly induce PGC-like cells (PGCLCs) in EpiLCs, but not in ES cells6, 7, 8. Here we report an unexpected discovery that Nanog alone can induce PGCLCs in EpiLCs, independently of BMP4. We propose that after the dissolution of the naive ES-cell pluripotency network during establishment of EpiLCs9, 10, the epigenome is reset for cell fate determination. Indeed, we found genome-wide changes in NANOG-binding patterns between ES cells and EpiLCs, indicating epigenetic resetting of regulatory elements. Accordingly, we show that NANOG can bind and activate enhancers of Prdm1 and Prdm14 in EpiLCs in vitro; BLIMP1 (encoded by Prdm1) then directly induces Tfap2c. Furthermore, while SOX2 and NANOG promote the pluripotent state in ES cells, they show contrasting roles in EpiLCs, as Sox2 specifically represses PGCLC induction by Nanog. This study demonstrates a broadly applicable mechanistic principle for how cells acquire competence for cell fate determination, resulting in the context-dependent roles of key transcription factors during development.

Pub.: 11 Jan '16, Pinned: 03 Jul '17

Induction of mouse germ-cell fate by transcription factors in vitro.

Abstract: The germ-cell lineage ensures the continuity of life through the generation of male and female gametes, which unite to form a totipotent zygote. We have previously demonstrated that, by using cytokines, embryonic stem cells and induced pluripotent stem cells can be induced into epiblast-like cells (EpiLCs) and then into primordial germ cell (PGC)-like cells with the capacity for both spermatogenesis and oogenesis, creating an opportunity for understanding and regulating mammalian germ-cell development in both sexes in vitro. Here we show that, without cytokines, simultaneous overexpression of three transcription factors, Blimp1 (also known as Prdm1), Prdm14 and Tfap2c (also known as AP2γ), directs EpiLCs, but not embryonic stem cells, swiftly and efficiently into a PGC state. Notably, Prdm14 alone, but not Blimp1 or Tfap2c, suffices for the induction of the PGC state in EpiLCs. The transcription-factor-induced PGC state, irrespective of the transcription factors used, reconstitutes key transcriptome and epigenetic reprogramming in PGCs, but bypasses a mesodermal program that accompanies PGC or PGC-like-cell specification by cytokines including bone morphogenetic protein 4. Notably, the transcription-factor-induced PGC-like cells contribute to spermatogenesis and fertile offspring. Our findings provide a new insight into the transcriptional logic for PGC specification, and create a foundation for the transcription-factor-based reconstitution and regulation of mammalian gametogenesis.

Pub.: 06 Aug '13, Pinned: 30 Jun '17