Gro/TLE enables embryonic stem cell differentiation by repressing pluripotent gene expression.

Gro/TLE proteins (TLE1-4) are a family of transcriptional corepressors acting downstream of multiple signalling pathways. Several TLEs are expressed in a dynamic manner throughout embryonic development and at high levels in embryonic stem cells (ESCs). Here we find that Gro/TLE is not required in ESC for sustaining pluripotency and suppressing differentiation genes, but rather is important for the shutting down of the pluripotency network in differentiation. Consistent with this view, we found that one of the Gro/TLE family, TLE4 is expressed heterogeneously in ESCs in a population that corresponds to a Nanog low subset of ESC culture. TLE4 expression is also increased in response to LIF withdrawal and Fgf/Mek/Erk stimulation. To explore the role of Gro/TLE in more detail we generated an allelic series of knockout ESCs of two TLE genes expressed most dynamically in early differentiation, TLE3 and TLE4. Genetic reduction in TLE dose resulted in an increase in the expression of pluripotency markers and inhibition of ESC differentiation towards both epiblast and endoderm lineages. Overexpression of a drug inducible TLE4 could both rescue TLE3/TLE4 compound phenotypes and induce early expression of endoderm (Hhex-Venus) and neural (Sox1-GFP) reporter genes. Taken together, our results suggest that TLE activity is essential for early differentiation where it acts to suppress the pluripotency network, allowing for the initiation of lineage specific gene expression programs.

An automated microfluidic device for time-lapse imaging of mouse embryonic stem cells.

Long-term, time-lapse imaging studies of embryonic stem cells (ESCs) require a controlled and stable culturing environment for high-resolution imaging. Microfluidics is well-suited for such studies, especially when the media composition needs to be rapidly and accurately altered without disrupting the imaging. Current studies in plates, which can only add molecules at the start of an experiment without any information on the levels of endogenous signaling before the exposure, are incompatible with continuous high-resolution imaging and cell-tracking. Here, we present a custom designed, fully automated microfluidic chip to overcome these challenges. A unique feature of our chip includes three-dimensional ports that can connect completely sealed on-chip valves for fluid control to individually addressable cell culture chambers with thin glass bottoms for high-resolution imaging. We developed a robust protocol for on-chip culturing of mouse ESCs for minimum of 3 days, to carry out experiments reliably and repeatedly. The on-chip ESC growth rate was similar to that on standard culture plates with same initial cell density. We tested the chips for high-resolution, time-lapse imaging of a sensitive reporter of ESC lineage priming, Nanog-GFP, and HHex-Venus with an H2B-mCherry nuclear marker for cell-tracking. Two color imaging of cells was possible over a 24-hr period while maintaining cell viability. Importantly, changing the media did not affect our ability to track individual cells. This system now enables long-term fluorescence imaging studies in a reliable and automated manner in a fully controlled microenvironment.