Transcriptional regulation of Tal2 gene by all-trans retinoic acid (atRA) in P19 cells

Expression and Regulation of Tal2 during Neuronal Differentiation in P19 Cells

T-cell acute lymphocytic leukemia 2 (Tal2) is a gene encoding a member of the basic helix-loop-helix transcription factor family, which is essential for the normal development of the mouse brain. We found that Tal2 was induced during neural differentiation in P19 cells, which are pluripotent mouse embryonal carcinoma cells that differentiate into the neural lineage upon both exposure to all-trans retinoic acid (atRA) and the formation of cell aggregation. Tal2 expression during neural differentiation in P19 cells was detected within 3 h after induction with atRA and retinoic acid receptor α (RARα). The atRA-RARα complex is known to bind to a characteristic retinoic acid response element (RARE) located in the promoter of target genes. We found a RARE-like element in the intron of Tal2. We also found a TATA-box-like element in the 5' region. The TATA-box-like element functioned as a core promoter, and TATA- box binding protein bound to this element upstream of Tal2 in P19 cells. The RARE-like element responded to atRA signaling that activated the transcription, and RARα was bound to this element in the intron of Tal2 in P19 cells. Furthermore, the interaction between these elements on Tal2 was confirmed in a chromatin immunoprecipitation assay. Because the neural differentiation of P19 cells mimics in part the development of the nervous system, P19 cells are useful for studying the mechanism underlying the role of Tal2 in neural differentiation. Further work is underway to clarify the function of Tal2 in neural differentiation using the differentiation system of P19 cells.

Reconstructed cell fate-regulatory programs in stem cells reveal hierarchies and key factors of neurogenesis

Cell lineages, which shape the body architecture and specify cell functions, derive from the integration of a plethora of cell intrinsic and extrinsic signals. These signals trigger a multiplicity of decisions at several levels to modulate the activity of dynamic gene regulatory networks (GRNs), which ensure both general and cell-specific functions within a given lineage, thereby establishing cell fates. Significant knowledge about these events and the involved key drivers comes from homogeneous cell differentiation models. Even a single chemical trigger, such as the morphogen all-trans retinoic acid (RA), can induce the complex network of gene-regulatory decisions that matures a stem/precursor cell to a particular step within a given lineage. Here we have dissected the GRNs involved in the RA-induced neuronal or endodermal cell fate specification by integrating dynamic RXRA binding, chromatin accessibility, epigenetic promoter epigenetic status, and the transcriptional activity inferred from RNA polymerase II mapping and transcription profiling. Our data reveal how RA induces a network of transcription factors (TFs), which direct the temporal organization of cognate GRNs, thereby driving neuronal/endodermal cell fate specification. Modeling signal transduction propagation using the reconstructed GRNs indicated critical TFs for neuronal cell fate specification, which were confirmed by CRISPR/Cas9-mediated genome editing. Overall, this study demonstrates that a systems view of cell fate specification combined with computational signal transduction models provides the necessary insight in cellular plasticity for cell fate engineering. The present integrated approach can be used to monitor the in vitro capacity of (engineered) cells/tissues to establish cell lineages for regenerative medicine.

Methylation of the Gpat2 promoter regulates transient expression during mouse spermatogenesis

We studied the expression pattern and the mechanisms governing the transcription of GPAT2, an enzyme that is highly expressed in testis. GPAT2 is regulated epigenetically and its expression correlates with the initiation of meiosis.

Spermatogenesis is a highly regulated process that involves both mitotic and meiotic divisions, as well as cellular differentiation to yield mature spermatozoa from undifferentiated germinal stem cells. Although Gpat2 was originally annotated as encoding a glycerol-3-phosphate acyltransferase by sequence homology to Gpat1, GPAT2 is highly expressed in testis but not in lipogenic tissues and is not up-regulated during adipocyte differentiation. New data show that GPAT2 is required for the synthesis of piRNAs (piwi-interacting RNAs), a group of small RNAs that protect the germ cell genome from retrotransposable elements. In order to understand the relationship between GPAT2 and its role in the testis, we focused on Gpat2 expression during the first wave of mouse spermatogenesis. Gpat2 expression was analysed by qPCR (quantitative real-time PCR), in situ hybridization, immunohistochemistry and Western blotting. Gpat2 mRNA content and protein expression were maximal at 15 dpp (days post-partum) and were restricted to pachytene spermatocytes. To achieve this transient expression, both epigenetic mechanisms and trans-acting factors are involved. In vitro assays showed that Gpat2 expression correlates with DNA demethylation and histone acetylation and that it is up-regulated by retinoic acid. Epigenetic regulation by DNA methylation was confirmed in vivo in germ cells by bisulfite sequencing of the Gpat2 promoter. Consistent with the initiation of meiosis at 11 dpp, methylation decreased dramatically. Thus, Gpat2 is expressed at a specific stage of spermatogenesis, consistent with piRNA synthesis and meiosis I prophase, and its on–off expression pattern responds predominantly to epigenetic modifications.