FACT maintains nucleosomes during transcription and stem cell viability in adult mice

Abstract

Preservation of nucleosomes during replication has been extensively studied, while the maintenance of nucleosomes during transcription has gotten less attention. The histone chaperone FACT has a role in transcription elongation, although whether it disassembles or assembles nucleosomes during this process is unclear.To elucidate the function of FACT in mammals, we deleted the Ssrp1 subunit of FACT in adult mice. FACT loss is lethal, possibly due to the loss of the earliest progenitors in bone marrow and intestine, while more differentiated cells are not affected. Using cells isolated from several tissues, we show that FACT loss reduces the viability of stem cells but not of cells differentiated in vitro. FACT depletion increases chromatin accessibility in a transcriptiondependent manner in adipose mesenchymal stem cells, indicating that nucleosomes are lost in these cells during transcription in the absence of FACT. We also observe activation of interferon (IFN) signaling and the accumulation of immunocytes in organs sensitive to FACT loss. Our data indicate that FACT maintains chromatin integrity during transcription in mammalian adult stem cells, suggesting that chromatin transcription in stem cells and differentiated cells is different.

FACT regulates pluripotency through distal regulation of gene expression in murine embryonic stem cells

“…The amount of FACT-dependent mRNA transcription (both stimulated and repressed) are largely consistent between our data and experiments performed in S. cerevisiae (Feng et al, 2016), ES cell lines (F. Chen et al, 2020), and in a mouse model (Goswami et al, 2022), suggesting conservation of FACT function throughout eukaryotes.…”

“…As many groups have suggested, the act of transcription by RNAPII itself may be responsible for destabilization of nucleosomes, creating a genomic conflict for FACT to resolve (Farnung et al, 2021; Formosa & Winston, 2020; Goswami et al, 2022; Célia Jeronimo et al, 2020; Y. Liu et al, 2020).…”

“…Interestingly, SSRP1 knockout in murine ES cells is viable and shows no effect on expression of the pluripotency factor OCT4 (F. Chen et al, 2020); however, conditional knockout of SSRP1 in mice is lethal due to a loss of progenitor cells resulting in hematopoietic and intestinal failures (Goswami et al, 2022). These disparities may be related to described FACT-independent roles of SSRP1 (Y.…”

Pluripotency state transition of embryonic stem cells requires the turnover of histone chaperone FACT on chromatin

“…It was reported that the mouse with deletion of the Ssrp1 gene could not survive to adulthood, and loss of SSRP1 reduces the viability of stem cells in several tissues. 53 , 54 We analyzed the effect of SSRP1-Q265K mutation on the growth and pluripotency of mESCs. We first cultured wild-type and Ssrp1 Q265K mESCs in the standard SL2i medium, which contains serum (S), leukemia inhibitory factor (L), and two inhibitors (2i) that inhibit GSK3β (GSKi) and MEK1/2 (MEKi), respectively.…”

Transcriptional regulation of FACT involves Coordination of chromatin accessibility and CTCF binding

“…FACT also plays a role in suppressing cryptic transcription ( 9 , 10 ), silencing heterochromatin ( 11 , 12 ), and inhibiting expression of subtelomeric genes and MERVL retrotransposon ( 13 , 14 , 15 , 16 ). Intriguingly, FACT is abundantly expressed in undifferentiated or tumor cells, while it has very limited expression in differentiated cells, suggesting possible involvement in maintenance of undifferentiated cell status ( 17 , 18 , 19 ). Substantial progress has been made in understanding the structural features of FACT and its roles in development and carcinogenesis ( 20 , 21 , 22 ).…”