RNA polymerase II transcription initiation in holo-TFIID-depleted mouse embryonic stem cells.

The recognition of core promoter sequences by TFIID is the first step in RNA polymerase II (Pol II) transcription initiation. Metazoan holo-TFIID is a trilobular complex, composed of the TATA binding protein (TBP) and 13 TBP-associated factors (TAFs). Why and how TAFs are necessary for the formation of TFIID domains and how they contribute to transcription initiation remain unclear.

De novo variants in ATXN7L3 lead to developmental delay, hypotonia and distinctive facial features.

Deubiquitination is crucial for the proper functioning of numerous biological pathways, such as DNA repair, cell cycle progression, transcription, signal transduction and autophagy. Accordingly, pathogenic variants in deubiquitinating enzymes (DUBs) have been implicated in neurodevelopmental disorders and congenital abnormalities. ATXN7L3 is a component of the DUB module of the Spt-Ada-Gcn5 acetyltransferase (SAGA) complex and two other related DUB modules, and it serves as an obligate adaptor protein of three ubiquitin-specific proteases (USP22, USP27X or USP51).

RNA polymerase II transcription with partially assembled TFIID complexes.

The recognition of core promoter sequences by the general transcription factor TFIID is the first step in the process of RNA polymerase II (Pol II) transcription initiation. Metazoan holo-TFIID is composed of the TATA binding protein (TBP) and of 13 TBP associated factors (TAFs). Inducible knock out (KO) results in the formation of a Taf7-less TFIID complex, while KO leads to serious defects within the TFIID assembly pathway.

ATAC and SAGA co-activator complexes utilize co-translational assembly, but their cellular localization properties and functions are distinct.

To understand the function of multisubunit complexes, it is of key importance to uncover the precise mechanisms that guide their assembly. Nascent proteins can find and bind their interaction partners during their translation, leading to co-translational assembly. Here, we demonstrate that the core modules of ATAC (ADA-two-A-containing) and SAGA (Spt-Ada-Gcn5-acetyltransferase), two lysine acetyl transferase-containing transcription co-activator complexes, assemble co-translationally in the cytoplasm of mammalian cells.

ATAC and SAGA coactivator complexes utilize co-translational assembly, but their cellular localization properties and functions are distinct.

To understand the function of multisubunit complexes it is of key importance to uncover the precise mechanisms that guide their assembly. Nascent proteins can find and bind their interaction partners during their translation, leading to co-translational assembly. Here we demonstrate that the core modules of ATAC (ADA-Two-A-Containing) and SAGA (Spt-Ada-Gcn5-acetyltransferase), two lysine acetyl transferase-containing transcription coactivator complexes, assemble co-translationally in the cytoplasm of mammalian cells.

The Transcriptional Regulator Is Essential for the Early Development of the Sensory Whisker Follicle and Is Linked to the Beta-Catenin First Dermal Signal.

mutant mice are one of the rare mutant strains that do not develop whisker hair follicles while still displaying a pelage. Here, we show that is expressed at the earliest stage of whisker development in clusters of mesenchymal cells before placode formation. Its conditional knockout in the murine soma leads to the loss of expression of , , , , , and , though leaving the β-catenin-driven first dermal signal intact.

SUPT3H-less SAGA coactivator can assemble and function without significantly perturbing RNA polymerase II transcription in mammalian cells.

Coactivator complexes regulate chromatin accessibility and transcription. SAGA (Spt-Ada-Gcn5 Acetyltransferase) is an evolutionary conserved coactivator complex. The core module scaffolds the entire SAGA complex and adopts a histone octamer-like structure, which consists of six histone-fold domain (HFD)-containing proteins forming three histone-fold (HF) pairs, to which the double HFD-containing SUPT3H adds one HF pair.

SAGA-Dependent Histone H2Bub1 Deubiquitination Is Essential for Cellular Ubiquitin Balance during Embryonic Development.

Ubiquitin (ub) is a small, highly conserved protein widely expressed in eukaryotic cells. Ubiquitination is a post-translational modification catalyzed by enzymes that activate, conjugate, and ligate ub to proteins. Substrates can be modified either by addition of a single ubiquitin molecule (monoubiquitination), or by conjugation of several ubs (polyubiquitination).

What defines the maternal transcriptome?

In somatic cells, RNA polymerase II (Pol II) transcription initiation starts by the binding of the general transcription factor TFIID, containing the TATA-binding protein (TBP) and 13 TBP-associated factors (TAFs), to core promoters. However, in growing oocytes active Pol II transcription is TFIID/TBP-independent, as during oocyte growth TBP is replaced by its vertebrate-specific paralog TBPL2. TBPL2 does not interact with TAFs, but stably associates with TFIIA.

Histone H2Bub1 deubiquitylation is essential for mouse development, but does not regulate global RNA polymerase II transcription.

Co-activator complexes dynamically deposit post-translational modifications (PTMs) on histones, or remove them, to regulate chromatin accessibility and/or to create/erase docking surfaces for proteins that recognize histone PTMs. SAGA (Spt-Ada-Gcn5 Acetyltransferase) is an evolutionary conserved multisubunit co-activator complex with modular organization. The deubiquitylation module (DUB) of mammalian SAGA complex is composed of the ubiquitin-specific protease 22 (USP22) and three adaptor proteins, ATXN7, ATXN7L3 and ENY2, which are all needed for the full activity of the USP22 enzyme to remove monoubiquitin (ub1) from histone H2B.

TBPL2/TFIIA complex establishes the maternal transcriptome through oocyte-specific promoter usage.

During oocyte growth, transcription is required to create RNA and protein reserves to achieve maternal competence. During this period, the general transcription factor TATA binding protein (TBP) is replaced by its paralogue, TBPL2 (TBP2 or TRF3), which is essential for RNA polymerase II transcription. We show that in oocytes TBPL2 does not assemble into a canonical TFIID complex.

Glycogen Dynamics Drives Lipid Droplet Biogenesis during Brown Adipocyte Differentiation.

Browning induction or transplantation of brown adipose tissue (BAT) or brown/beige adipocytes derived from progenitor or induced pluripotent stem cells (iPSCs) can represent a powerful strategy to treat metabolic diseases. However, our poor understanding of the mechanisms that govern the differentiation and activation of brown adipocytes limits the development of such therapy. Various genetic factors controlling the differentiation of brown adipocytes have been identified, although most studies have been performed using in vitro cultured pre-adipocytes.

Co-translational assembly of mammalian nuclear multisubunit complexes.

Cells dedicate significant energy to build proteins often organized in multiprotein assemblies with tightly regulated stoichiometries. As genes encoding subunits assembling in a multisubunit complex are dispersed in the genome of eukaryotes, it is unclear how these protein complexes assemble. Here, we show that mammalian nuclear transcription complexes (TFIID, TREX-2 and SAGA) composed of a large number of subunits, but lacking precise architectural details are built co-translationally.

The TAF10-containing TFIID and SAGA transcriptional complexes are dispensable for early somitogenesis in the mouse embryo.

During development, tightly regulated gene expression programs control cell fate and patterning. A key regulatory step in eukaryotic transcription is the assembly of the pre-initiation complex (PIC) at promoters. PIC assembly has mainly been studied , and little is known about its composition during development.

Endothelial cell specification in the somite is compromised in Pax3-positive progenitors of Foxc1/2 conditional mutants, with loss of forelimb myogenesis.

Pax3 and Foxc2 have been shown genetically to mutually repress each other in the mouse somite. Perturbation of this balance in multipotent cells of the dermomyotome influences cell fate; upregulation of Foxc2 favours a vascular fate, whereas higher levels of Pax3 lead to myogenesis. Foxc1 has overlapping functions with Foxc2.

The SAGA coactivator complex acts on the whole transcribed genome and is required for RNA polymerase II transcription.

The SAGA (Spt-Ada-Gcn5 acetyltransferase) coactivator complex contains distinct chromatin-modifying activities and is recruited by DNA-bound activators to regulate the expression of a subset of genes. Surprisingly, recent studies revealed little overlap between genome-wide SAGA-binding profiles and changes in gene expression upon depletion of subunits of the complex. As indicators of SAGA recruitment on chromatin, we monitored in yeast and human cells the genome-wide distribution of histone H3K9 acetylation and H2B ubiquitination, which are respectively deposited or removed by SAGA.

Notch regulation of myogenic versus endothelial fates of cells that migrate from the somite to the limb.

Multipotent Pax3-positive (Pax3(+)) cells in the somites give rise to skeletal muscle and to cells of the vasculature. We had previously proposed that this cell-fate choice depends on the equilibrium between Pax3 and Foxc2 expression. In this study, we report that the Notch pathway promotes vascular versus skeletal muscle cell fates.

Prdm1 functions in the mesoderm of the second heart field, where it interacts genetically with Tbx1, during outflow tract morphogenesis in the mouse embryo.

Congenital heart defects affect at least 0.8% of newborn children and are a major cause of lethality prior to birth. Malformations of the arterial pole are particularly frequent.

Mice carrying a hypomorphic Evi1 allele are embryonic viable but exhibit severe congenital heart defects.

The ecotropic viral integration site 1 (Evi1) oncogenic transcription factor is one of a number of alternative transcripts encoded by the Mds1 and Evi1 complex locus (Mecom). Overexpression of Evi1 has been observed in a number of myeloid disorders and is associated with poor patient survival. It is also amplified and/or overexpressed in many epithelial cancers including nasopharyngeal carcinoma, ovarian carcinoma, ependymomas, and lung and colorectal cancers.

Non conservation of function for the evolutionarily conserved prdm1 protein in the control of the slow twitch myogenic program in the mouse embryo.

Muscles are composed of multinucleated muscle fibers with different contractile and physiological properties, which result from specific slow or fast gene expression programs in the differentiated muscle cells. In the zebra fish embryo, the slow program is under the control of Hedgehog signaling from the notochord and floor plate. This pathway activates the expression of the conserved transcriptional repressor, Prdm1 (Blimp1), which in turn represses the fast program and promotes the slow program in adaxial cells of the somite and their descendants.

How to make a heart: the origin and regulation of cardiac progenitor cells.

The formation of the heart is a complex morphogenetic process that depends on the spatiotemporally regulated contribution of cardiac progenitor cells. These mainly derive from the splanchnic mesoderm of the first and second heart field (SHF), with an additional contribution of neurectodermally derived neural crest cells that are critical for the maturation of the arterial pole of the heart. The origin and distinguishing characteristics of the two heart fields, as well as the relation of the SHF to the proepicardial organ and to a proposed third heart field are still subjects of debate.

Role of mesodermal FGF8 and FGF10 overlaps in the development of the arterial pole of the heart and pharyngeal arch arteries.

Rationale: The genes encoding fibroblast growth factor (FGF) 8 and 10 are expressed in the anterior part of the second heart field that constitutes a population of cardiac progenitor cells contributing to the arterial pole of the heart. Previous studies of hypomorphic and conditional Fgf8 mutants show disrupted outflow tract (OFT) and right ventricle (RV) development, whereas Fgf10 mutants do not have detectable OFT defects.

Objectives: Our aim was to investigate functional overlap between Fgf8 and Fgf10 during formation of the arterial pole.

Distinct and dynamic myogenic populations in the vertebrate embryo.

Myogenic cells in the body of vertebrates derive from the dorsal somite, the dermomyotome, where multipotent cells are present. Regulation of cell fate choice is discussed, as is that of progenitor cell self-renewal once cells have entered the myogenic programme. Ongoing research on the formation of the first skeletal muscle, the myotome, is presented with emphasis on mechanisms controlling the early segregation of slow and fast muscle lineages that characterizes this process in the zebrafish embryo.

The A17 enhancer directs expression of Myf5 to muscle satellite cells but Mrf4 to myonuclei.

The myogenic regulatory factors, Myf5 and Mrf4, play key roles in the specification and differentiation of skeletal muscle, respectively. Many cis-acting regulatory elements at the Mrf4/Myf5 locus have been identified, including the A17 enhancer. During development, A17 in conjunction with the Mrf4 or Myf5 promoter, directs transgene expression either to embryonic or fetal muscles.

The zinc finger transcriptional repressor Blimp1/Prdm1 is dispensable for early axis formation but is required for specification of primordial germ cells in the mouse.

Blimp1, a zinc-finger containing DNA-binding transcriptional repressor, functions as a master regulator of B cell terminal differentiation. Considerable evidence suggests that Blimp1 is required for the establishment of anteroposterior axis formation and the formation of head structures during early vertebrate development. In mouse embryos, Blimp1 is strongly expressed in axial mesendoderm, the tissue known to provide anterior patterning signals during gastrulation.