Zenke

Project Title: Reprogramming and somatic memory in ES cell/hematopoietic cell hybrids

In this project we study somatic memory in pluripotent cells derived from hematopoietic stem cells (HSC) by (i) fusion with embryonic stem cells (ESC) and (ii) transduction with reprogramming transcription factors. Flt3+ HSC from bone marrow of Oct4-eGFP transgenic mice were fused with ESC to generate Oct4-eGFP+ reprogrammed Flt3 HSC/ESC hybrids. These Flt3 ESC hybrids were pluripotent, showed ESC morphology and an ESC-like gene expression profile, but surprisingly contained somatic memory. Flt3+ HSC from Oct4-eGFP transgenic mice were transduced with the four reprogramming factors Oct4, Sox2, c-Myc and Klf4 to obtain Oct4-eGFP+ induced pluripotent stem cells (Flt3 iPS cells). Pluripotency and somatic memory in Flt3 ESC hybrids and Flt3 iPS cells were studied in in vitro culture systems and following transfer into recipient mice in vivo. We found that Flt3 ESC hybrids with somatic memory differentiated in embryoid body (EB) assays with accelerated kinetics. Additionally, such EB exhibited a well-structured tissue organisation similar to a developing embryo. Flt3 iPS cells showed delayed differentiation kinetics and a moderate differentiation potential. Our studies focus now on obtaining detailed insights into the molecular basis of somatic memory in Flt3 ESC hybrids in vitro and in vivo.