Co-existence of intact stemness and priming of neural differentiation programs in mES cells lacking Trim71.

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.

Atad3 function is essential for early post-implantation development in the mouse.

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.

Transcriptional regulator BPTF/FAC1 is essential for trophoblast differentiation during early mouse development.

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 mouse Trm1-like gene is expressed in neural tissues and plays a role in motor coordination and exploratory behaviour.

Using a gene trap approach in ES cells, the novel mouse gene Trm1-like with substantial sequence homology to human C1orf25 mRNA (GenBank accession no. ) was identified. Murine Trm1-like encodes a putative protein with limited similarity to N2,N2-dimethylguanosine tRNA methyltransferase (Trm1) from other organisms, however its function is not known. The potential role of Trm1-like was investigated in a mouse mutant lacking intact Trm1-like transcripts due to integration of the gene trap vector in the first intron. Trm1-like deficient mice are viable and show no apparent anatomical defects. Behavioural tests, however, revealed significantly altered motor coordination and aberrant exploratory behaviour. LacZ activity of the trapped mouse Trm1-like gene reflects expression in various neuronal structures during embryonic development, including spinal ganglia, trigeminal nerve and ganglion, olfactory and nasopharyngeal epithelium, and nuclei of the metencephalon, thalamus and medulla oblongata. The gene is also expressed in lung, oesophagus, epiglottis, ependyma, vertebral column, spinal cord, and brown adipose tissue. Trm1-like expression persists in the adult brain with dynamically changing patterns in cortex and cerebellum. Although Trm1-like is not essential for embryonic mouse development, it may have a role in modulating postnatal neuronal functions.