Regulatory networks for differentiation and pluripotency in embryonic stem (ES) cells have long been suggested to be mutually exclusive. However, with the identification of many new components of these networks ranging from epigenetic, transcriptional, and translational to even post-translational mechanisms, the cellular states of pluripotency and early differentiation might not be strictly bi-modal, but differentiating stem cells appear to go through phases of simultaneous expression of stemness and differentiation genes. Translational regulators such as RNA binding proteins (RBPs) and micro RNAs (miRNAs) might be prime candidates for guiding a cell from pluripotency to differentiation. Using Trim71, one of two members of the Tripartite motif (Trim) protein family with RNA binding activity expressed in murine ES cells, we demonstrate that Trim71 is not involved in regulatory networks of pluripotency but regulates neural differentiation. Loss of Trim71 in mES cells leaves stemness and self-maintenance of these cells intact, but many genes required for neural development are up-regulated at the same time. Concordantly, Trim71−/− mES show increased neural marker expression following treatment with retinoic acid. Our findings strongly suggest that Trim71 keeps priming steps of differentiation in check, which do not pre-require a loss of the pluripotency network in ES cells.

The mitochondrial AAA+-ATPase ATAD3 is implicated in the regulation of mitochondrial and ER dynamics and was shown to be necessary for larval development in Caenorhabditis elegans. In order to elucidate the relevance of ATAD3 for mammalian development, the phenotype of an Atad3 deficient mouse line was analyzed. Atad3 deficient embryos die around embryonic day E7.5 due to growth retardation and a defective development of the trophoblast lineage immediately after implantation into the uterus. This indicates an essential function of Atad3 for the progression of the first steps of post-implantation development at a time point when mitochondrial biogenesis and ATP production by oxidative phosphorylation are required. Therefore, murine Atad3 plays an important role in the biogenesis of mitochondria in trophoblast stem cells and in differentiating trophoblasts. At the biochemical level, we report here that ATAD3 is present in five native mitochondrial protein complexes of different sizes, indicating complex roles of the protein in mitochondrial architecture and function.

The putative transcriptional regulator BPTF/FAC1 is expressed in embryonic and extraembryonic tissues of the early mouse conceptus. The extraembryonic trophoblast lineage in mammals is essential to form the fetal part of the placenta and hence for the growth and viability of the embryo in utero. Here, we describe a loss-of-function allele of the BPTF/FAC1 gene that causes embryonic lethality in the mouse. BPTF/FAC1-deficient embryos form apparently normal blastocysts that implant and develop epiblast, visceral endoderm, and extraembryonic ectoderm including trophoblast stem cells. Subsequent development of mutants, however, is arrested at the early gastrula stage (embryonic day 6.5), and virtually all null embryos die before midgestation. Most notably, the ectoplacental cone is drastically reduced or absent in mutants, which may cause the embryonic lethality. Development of the mutant epiblast is also affected, as the anterior visceral endoderm and the primitive streak do not form correctly, while brachyury-expressing mesodermal cells arise but are delayed. The mutant phenotype suggests that gastrulation is initiated, but no complete anteroposterior axis of the epiblast appears. We conclude that BPTF/FAC1 is essential in the extraembryonic lineage for correct development of the ectoplacental cone and fetomaternal interactions. In addition, BPTF/FAC1 may also play a role either directly or indirectly in anterior-posterior patterning of the epiblast.The bromodomain plant homeodomain transcription factor (BPTF) in mammals represents the orthologue of the Drosophila nucleosome remodeling factor NURF301, which constitutes the largest subunit of the NURF chromatin remodeling complex (48). Human BPTF consists of 2,781 amino acids (23), and the sequence contains typical features of a transcriptional regulator, such as the DDT DNA binding domain, the PHD/LAP zinc finger (9, 52), a putative histone acetylating bromodomain of 110 amino acids (21, 51), a glutamine-rich acidic transcriptional activation domain, and nuclear import and export signals. It has been demonstrated that BPTF in Drosophila participates in the regulation of engrailed 1 and 2 expression as part of the NURF complex, presumably by changing the periodic alignment of nucleosomes (2). The fetal ALZ50-reactive clone 1 (FAC1) was discovered in amyloid plaques of patients with Alzheimer disease (5, 22), and it is likely to be a shorter transcript of the BPTF gene. FAC1 encompasses 801 N-terminal amino acids of BPTF but lacks the C-terminal bromodomain. It was proposed that FAC1 acts as transcriptional regulator on a DNA consensus sequence (FAC1 binding element) which is present in several genes that have been implicated in neurodegenerative disorders, including presenilin-1, amyloid precursor protein, dopamine D2 receptor, and Cu 2ϩ /Zn 2ϩ superoxide dismutase (25). During cortical brain development the protein is found in soma and neurites of various neurons (5). A BPTF/FAC1 orthologue was also identified in rat based on sequence conservation and similar doma...

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