Single-cell analysis reveals X upregulation is not global in pre-gastrulation embryos

Lineage-specific dynamics of erasure of X-upregulation during inactive-X reactivation

“…Therefore, maintenance of appropriate dosage of X-linked gene expression relative to autosomal genes in different developmental contexts is crucial. Recently, studies by us and others have shown that the upregulation of active-X chromosome both in male and female cells during early development fine-tunes the X-linked gene expression as proposed by Ohno (Lentini et al, 2022; Mandal et al, 2020; Naik et al, 2022). Importantly, we demonstrated that during the initiation of random X-inactivation in female pre-gastrulation embryos, X-upregulation happens in a highly coordinated manner along with the X-inactivation (Naik et al, 2022).…”

“…While X-inactivation has been extensively studied, the existence of active-X upregulation remains controversial and has been challenged for a long time (Chen and Zhang, 2016; Deng et al, 2011; Julien et al, 2012; Kaur et al, 2020; Kharchenko et al, 2011; Xiong et al, 2010). Recent studies by us and others have provided substantial shreds of evidence for the existence of upregulated active-X chromosome in both male and female cells in mouse and human (Deng et al, 2013; Larsson et al, 2019; Lentini et al, 2022; Li et al, 2017; Lin et al, 2011; Mandal et al, 2020; De Mello et al, 2017; Naik et al, 2022; Sangrithi et al, 2017). However, the developmental dynamics of X-upregulation have not been explored much.…”

“…However, the developmental dynamics of X-upregulation have not been explored much. Recently, through single-cell analysis, we have demonstrated that X-upregulation happens concomitantly upon initiation of X-inactivation in pre-gastrulating mouse embryos (Naik et al, 2022). Overall, it is believed that two X-chromosomes in female cells coordinate with each other to fine-tune the X-linked gene expression during early development.…”

“…On the other hand, mechanistic aspects of X-chromosome upregulation/erasure of X-upregulation and how two X-chromosomes in female cells coordinate with each other remain poorly understood. It is thought that increased transcriptional burst frequency and enrichment of different active chromatin marks on the active-X drive the X-upregulation (Larsson et al, 2019; Naik et al, 2022). However, what drives the erasure of X-upregulation during the reactivation of the inactive-X is not known yet.…”

Controlled X‐chromosome dynamics defines meiotic potential of female mouse in vitro germ cells

“…This further highlights how timely X‐inactivation and ‐reactivation might be necessary for proper germ cell maturation (Fig 7 ). Moreover, while we acknowledge that our findings are based on data generated in vitro , we note that allele‐specific single‐cell RNA‐seq of E5.5‐E6.5 epiblast cells, the precursors of PGCs, revealed a considerable heterogeneity in X‐inactivation progression at this developmental time window (Mohammed et al , 2017 ; Cheng et al , 2019 ; preprint: Naik et al , 2021 ; Lentini et al , 2022 ), which could potentially allow cells to give rise to XaXa PGCs, similar to our XGFP+ PGCLCs. Indeed, when we analysed data from E6.5 epiblast in vivo (Cheng et al , 2019 ), we detected specifically in the proximal epiblast, which contains the competent precursor cells for PGC development (Lawson & Hage, 1994 ; Saitou et al , 2002 ), a high fraction of cells, which have not gone through X‐inactivation (Fig 3H and I ).…”