In Vivo Time-Lapse Imaging of Cell Divisions during Neurogenesis in the Developing Zebrafish Retina

AbstractTwo-photon excitation microscopy was used to reconstruct cell divisions in living zebrafish embryonic retinas. Contrary to proposed models for vertebrate asymmetric divisions, no apico-basal cell divisions take place in the zebrafish retina during the generation of postmitotic neurons. However, a surprising shift in the orientation of cell division from central-peripheral to circumferential occurs within the plane of the ventricular surface. In the sonic you (syu) and lakritz (lak) mutants, the shift from central-peripheral to circumferential divisions is absent or delayed, correlating with the delay in neuronal differentiation and neurogenesis in these mutants. The reconstructions here show that mitotic cells always remain in contact with the opposite basal surface by means of a thin basal process that can be inherited asymmetrically

stella Is a Maternal Effect Gene Required for Normal Early Development in Mice

Abstractstella is a novel gene specifically expressed in primordial germ cells, oocytes, preimplantation embryos, and pluripotent cells [1, 2]. It encodes a protein with a SAP-like domain [3] and a splicing factor motif-like structure, suggesting possible roles in chromosomal organization or RNA processing. Here, we have investigated the effects of a targeted mutation of stella in mice. We show that while matings between heterozygous animals resulted in the birth of apparently normal stella null offspring, stella-deficient females displayed severely reduced fertility due to a lack of maternally inherited Stella-protein in their oocytes. Indeed, we demonstrate that embryos without Stella are compromised in preimplantation development and rarely reach the blastocyst stage. stella is thus one of few known mammalian maternal effect genes [4–9], as the phenotypic effect on embryonic development is mainly a consequence of the maternal stella mutant genotype. Furthermore, we show that STELLA that is expressed in human oocytes [10] is also expressed in human pluripotent cells and in germ cell tumors. Interestingly, human chromosome 12p, which harbours STELLA, is consistently overrepresented in these tumors [11]. These findings suggest a similar role for STELLA during early human development as in mice and a potential involvement in germ cell tumors

Dynamics of alternative splicing during somatic cell reprogramming reveals functions for RNA-binding proteins CPSF3, hnRNP UL1, and TIA1

C.V. was recipient of an FPI-Severo Ochoa Fellowship from the Spanish Ministry of Economy and Competitiveness. Work in J.V. laboratory is supported by the European Research Council (ERC AdvG 670146), AGAUR, Spanish Ministry of Economy and Competitiveness (BFU 2017 89308-P) and the Centre of Excellence Severo Ochoa. Work in T.G.'s laboratory was supported by the European Research Council FP7/2007-2013 (ERC Synergy Grant 4D-Genome) the Ministerio de Educación y Ciencia (SAF.2012-37167) and AGAUR. We acknowledge support of the Spanish Ministry of Science and Innovation to the EMBL partnership and the CERCA Programme / Generalitat de Catalunya.UDTRIASBackground: Somatic cell reprogramming is the process that allows differentiated cells to revert to a pluripotent state. In contrast to the extensively studied rewiring of epigenetic and transcriptional programs required for reprogramming, the dynamics of post-transcriptional changes and their associated regulatory mechanisms remain poorly understood. Here we study the dynamics of alternative splicing changes occurring during efficient reprogramming of mouse B cells into induced pluripotent stem (iPS) cells and compare them to those occurring during reprogramming of mouse embryonic fibroblasts. Results: We observe a significant overlap between alternative splicing changes detected in the two reprogramming systems, which are generally uncoupled from changes in transcriptional levels. Correlation between gene expression of potential regulators and specific clusters of alternative splicing changes enables the identification and subsequent validation of CPSF3 and hnRNP UL1 as facilitators, and TIA1 as repressor of mouse embryonic fibroblasts reprogramming. We further find that these RNA-binding proteins control partially overlapping programs of splicing regulation, involving genes relevant for developmental and morphogenetic processes. Conclusions: Our results reveal common programs of splicing regulation during reprogramming of different cell types and identify three novel regulators of this process and their targets

Mst1 and Mst2 Maintain Hepatocyte Quiescence and Suppress Hepatocellular Carcinoma Development through Inactivation of the Yap1 Oncogene

Hippo-Lats-Yorkie signaling regulates tissue overgrowth and tumorigenesis in Drosophila. We show that the Mst1 and Mst2 protein kinases, the mammalian Hippo orthologs, are cleaved and constitutively activated in the mouse liver. Combined Mst1/2 deficiency in the liver results in loss of inhibitory Ser127 phosphorylation of the Yorkie ortholog, Yap1, massive overgrowth, and hepatocellular carcinoma (HCC). Reexpression of Mst1 in HCC-derived cell lines promotes Yap1 Ser127 phosphorylation and inactivation and abrogates their tumorigenicity. Notably, Mst1/2 inactivates Yap1 in liver through an intermediary kinase distinct from Lats1/2. Approximately 30% of human HCCs show low Yap1(Ser127) phosphorylation and a majority exhibit loss of cleaved, activated Mst1. Mst1/2 inhibition of Yap1 is an important pathway for tumor suppression in liver relevant to human HCC

Developmental regulation of X-chromosome inactivation

With the emergence of sex-determination by sex chromosomes, which differ in composition and number between males and females, appeared the need to equalize X-chromosomal gene dosage between the sexes. Mammals have devised the strategy of X-chromosome inactivation (XCI), in which one of the two X-chromosomes is rendered transcriptionally silent in females. In the mouse, the best-studied model organism with respect to XCI, this inactivation process occurs in different forms, imprinted and random, interspersed by periods of X-chromosome reactivation (XCR), which is needed to switch between the different modes of XCI. In this review, I describe the recent advances with respect to the developmental control of XCI and XCR and in particular their link to differentiation and pluripotency. Furthermore, I review the mechanisms, which influence the timing and choice, with which one of the two X-chromosomes is chosen for inactivation during random XCI. This has an impact on how females are mosaics with regard to which X-chromosome is active in different cells, which has implications on the severity of diseases caused by X-linked mutations.The work was supported by the Spanish Ministry of Economy and Competitiveness,'Centro de Excelencia Severo Ochoa 2013–2017', SEV-2012-0208 and for a Plan Estatal Grant to B.P. (BFU2014-55275-P

Developmental regulation of X-chromosome inactivation

With the emergence of sex-determination by sex chromosomes, which differ in composition and number between males and females, appeared the need to equalize X-chromosomal gene dosage between the sexes. Mammals have devised the strategy of X-chromosome inactivation (XCI), in which one of the two X-chromosomes is rendered transcriptionally silent in females. In the mouse, the best-studied model organism with respect to XCI, this inactivation process occurs in different forms, imprinted and random, interspersed by periods of X-chromosome reactivation (XCR), which is needed to switch between the different modes of XCI. In this review, I describe the recent advances with respect to the developmental control of XCI and XCR and in particular their link to differentiation and pluripotency. Furthermore, I review the mechanisms, which influence the timing and choice, with which one of the two X-chromosomes is chosen for inactivation during random XCI. This has an impact on how females are mosaics with regard to which X-chromosome is active in different cells, which has implications on the severity of diseases caused by X-linked mutations.The work was supported by the Spanish Ministry of Economy and Competitiveness,'Centro de Excelencia Severo Ochoa 2013–2017', SEV-2012-0208 and for a Plan Estatal Grant to B.P. (BFU2014-55275-P

The compleX balancing act of controlling X-chromosome dosage and how it impacts mammalian germline development

In female mammals, the two X chromosomes are subject to epigenetic gene regulation in order to balance X-linked gene dosage with autosomes and in relation to males, which have one X and one Y chromosome. This is achieved by an intricate interplay of several processes; X-chromosome inactivation and reactivation elicit global epigenetic regulation of expression from one X chromosome in a stage-specific manner, whilst the process of X-chromosome upregulation responds to this by fine-tuning transcription levels of the second X. The germline is unique in its function of transmitting both the genetic and epigenetic information from one generation to the next, and remodelling of the X chromosome is one of the key steps in setting the stage for successful development. Here, we provide an overview of the complex dynamics of X-chromosome dosage control during embryonic and germ cell development, and aim to decipher its potential role for normal germline competency

PRDM14 controls X-chromosomal and global epigenetic reprogramming of H3K27me3 in migrating mouse primordial germ cells

Background: In order to prepare the genome for gametogenesis, primordial germ cells (PGCs) undergo extensive epigenetic reprogramming during migration toward the gonads in mammalian embryos. This includes changes on a genome-wide scale and additionally in females the remodeling of the inactive X-chromosome to enable X-chromosome reactivation (XCR). However, if global remodeling and X-chromosomal remodeling are related, how they occur in PGCs in vivo in relation to their migration progress and which factors are important are unknown. Results: Here we identify the germ cell determinant PR-domain containing protein 14 (PRDM14) as the first known factor that is instrumental for both global reprogramming and X-chromosomal reprogramming in migrating mouse PGCs. We find that global upregulation of the repressive histone H3 lysine 27 trimethylation (H3K27me3) mark is PRDM14 dosage dependent in PGCs of both sexes. When focusing on XCR, we observed that PRDM14 is required for removal of H3K27me3 from the inactive X-chromosome, which, in contrast to global upregulation, takes place progressively along the PGC migration path. Furthermore, we show that global and X-chromosomal reprogramming of H3K27me3 are functionally separable, despite their common regulation by PRDM14. Conclusions: In summary, here we provide new insight and spatiotemporal resolution to the progression and regulation of epigenome remodeling along mouse PGC migration in vivo and link epigenetic reprogramming to its developmental context.This work has been funded by the Spanish Ministry of Science, Innovation and Universities (BFU2014-55275-P and BFU2017-88407-P), the AXA Research Fund and the Agencia de Gestio d’Ajuts Universitaris i de Recerca (AGAUR, 2017 SGR 346). We would like to thank the Spanish Ministry of Economy, Industry and Competitiveness (MEIC) to the EMBL partnership and to the “Centro de Excelencia Severo Ochoa.” We also acknowledge support of the CERCA Programme of the Generalitat de Catalunya

Editorial: gene regulation from the X-chromosome during development and disease

MA was funded by NIH NIAID grant AI134834 and by DOD Lupus grant W81XH-18-1-0635. Work in the lab of BP was funded by the Spanish Ministry of Science, Innovation and Universities (BFU2017-88407-P), the AXA Research Fund and the Agencia de Gestio d'Ajuts Universitaris i de Recerca (AGAUR, 2017 SGR 346). We would like to thank the Spanish Ministry of Economy, Industry and Competitiveness (MEIC) to the EMBL partnership and to the “Centro de Excelencia Severo Ochoa”. We also acknowledge support of the CERCA Programme of the Generalitat de Catalunya. CM was supported by the Agence Nationale de la Recherche (ANR-14-CE10-0017, ANR-18-CE12-0017), the Ligue Contre le Cancer, the LabEx “Who Am I?” (ANR-11-LABX-0071), the Association pour la Recherche contre le Cancer (ARC), the Association Française contre les Myopathies (AFM) and by the Université de Paris IdEx (ANR-18-IDEX-0001) funded by the French Government through its “Investments for the Future” progra

Causality in transcription and genome folding: Insights from X inactivation

The spatial organization of genomes is becoming increasingly understood. In mammals, where it is most investigated, this organization ties in with transcription, so an important research objective is to understand whether gene activity is a cause or a consequence of genome folding in space. In this regard, the phenomena of X-chromosome inactivation and reactivation open a unique window of investigation because of the singularities of the inactive X chromosome. Here we focus on the cause-consequence nexus between genome conformation and transcription and explain how recent results about the structural changes associated with inactivation and reactivation of the X chromosome shed light on this problem.This work was supported by the Spanish Ministry of Science, Innovation and Universities and the Agencia Estatal de Investigacion (AEI, BFU2017-88407-P, EUR2019-103817 to B.P.), the AXA Research Fund (to B.P.) and the Agencia de Gestio d'Ajuts Universitaris i de Recerca (AGAUR, 2017 SGR 346 to B.P.). We would like to thank the Spanish Ministry of Economy, Industry and Competitiveness (MEIC) to the EMBL partnership and to the “Centro de Excelencia Severo Ochoa”. We also acknowledge support of the CERCA Programme of the Generalitat de Catalunya. M.B. is supported by an EMBO postdoctoral fellowship (ALTF 682–2021). G.J.F is supported by NSERC (Discovery Grant RGPIN-2020-06377)