Abstract
Somatic cells can be reprogrammed into pluripotent stem cells with a minimal set of defined factors, Oct3/4, Sox2, Klf4, and c-Myc, also known as OKSM, although this reprogramming is somewhat inefficient. Recent work has identified other nuclear factors, including SALL4, that can synergize with the OSK factors to improve reprogramming dynamics, but the specific role of each of these factors remains poorly understood. In this study, we sought to learn more about the role of SALL4. We observed that SALL4 was the most significant factor in promoting OKS-induced reprogramming. To look for molecules downstream of SALL4, we screened a set of putative targets to determine whether they could promote OKS-induced reprogramming. We identified CECR2, a multidomain nuclear factor and histone acetyl-lysine reader, as a SALL4 effector. Mechanistically, we determined that SALL4 activates Cecr2 expression by directly binding to its promotor region. CECR2 in turn promotes reprogramming by forming a chromatin remodeling complex; this complex contained the SWI/SNF family member SMARCA1 and was dependent on CECR2’s DTT domain. In combination, our findings suggest that CECR2 is a novel reprogramming factor and works through a protein network to overcome epigenetic barriers during reprogramming.
Highlights
Somatic cells can be reprogramed into pluripotent stem cells by overexpression of a set of nuclear factors Oct4/Sox2/ Klf4/c-Myc (OKSM) or Yamanaka factors (1) in mouse, or Oct4/Sox2/Nanog/Lin[28] in human (2), alternatively
A set of nuclear factors were reported to play roles in induced pluripotent stem cell (iPSC) induction by replacing or combining with the Yamanaka factors. These nuclear factors can be categorized into two groups: (1) transcriptional factors, which can facilitate somatic cell reprogramming by binding to specific nuclear sequences or motifs, such as Glis[1] (3), Nr5a2 (4), Sall[4] (5, 6), Esrrb (7), Dax[1] (8), Zscan[4] (9), Tbx[3] (10), and Prdm[14] (11); (2) epigenetic regulators, which facilitate somatic cell reprogramming by altering the chromatin structure or DNA/histone modifications, such as Tet[1] (12, 13), Brg[1] (14)
We have reported a group of 7F factors (NanogEsrrb-Glis1-Jdp2-Kdm2b-Sall4-Mkk6) that can reprogram mouse fibroblasts into pluripotent stem cells with a 10% efficiency (15)
Summary
We have reported a group of 7F factors (NanogEsrrb-Glis1-Jdp2-Kdm2b-Sall4-Mkk6) that can reprogram mouse fibroblasts into pluripotent stem cells with a 10% efficiency (15). We performed ATAC-seq and showed by PCA analysis that, similar to RNA-seq, OKS+Sall[4] modulates the chromatin structure toward an ESC-like state more quickly than OKS+DsRed (Fig. 2E). PCA analysis shows little differences between OKS+Cecr[2] and OKS+DsRed samples (Fig. 4A) Pluripotent genes, such as Fzd[10], Zfp[42], and Zscan[10], Fbxo[15], have higher expression levels at later stage when Cecr[2] overexpressed (Fig. 4B), consistent with the higher efficiency. We compared the chromatin accessibility dynamics data from OKS+DsRed, OKS+Sall[4], and OKS+Cecr[2], and PCA analysis showed that the chromatin state of Cecr[2] is very close to Sall[4] group at the late stage of reprogramming (Fig. S4, A–C). (14)response to virus (19)axonogenesis (13)defense response to virus (19)positive regulation of cytokine production (6)regulation of nuclease activity (17)positive regulation of defense response (6)regulation of ribonuclease activity
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