A transcriptome landscape of mouse embryogenesis.

Coordinated regulation of genetic activity underpins formation of the body plan and morphogenesis of embryonic structures. In this issue of Developmental Cell, Mitiku and Baker describe a chronological series of transcriptomes of postimplantation mouse embryos at gastrulation and early organogenesis, providing a valuable resource for studying the dynamics of both genome-wide and gene-specific transcriptional activities that accompany mouse embryogenesis.

Gene expression pattern and progression of embryogenesis in the immediate post-implantation period of mouse development.

During development of the mouse conceptus from implantation to the early gastrula stage, a multitude of genes encoding structural proteins, transcription factors and components of signalling pathways are expressed in the extraembryonic and embryonic tissues derived from the trophectoderm and the inner cell mass. Some genes are expressed widely in the extraembryonic ectoderm, the visceral endoderm or the epiblast, while others display more restricted expression domains in these tissues or are expressed upon the specification of the germ layers at gastrulation. Overall, the developmental changes in gene expression mirror key events of embryogenesis, and reveal the regionalization of signalling activity and the emergence of tissue patterning.

Interaction of the MAGUK family member Acvrinp1 and the cytoplasmic domain of the Notch ligand Delta1.

The evolutionarily conserved Notch signal transduction pathway regulates cell fate and cellular differentiation in various tissues and has essential functions in embryonic patterning and tumorigenesis. Cell-cell signaling by the Notch pathway is mediated by the interaction of the transmembrane receptor Notch with its ligands Delta or Jagged presented on adjacent cells. Whereas signal transduction to Notch expressing cells has been described, it is unclear whether Delta-dependent signaling may exist within the Delta-expressing cell. Here, we report on the identification of Acvrinp1, a MAGUK family member, interacting with the intracellular domain of Delta1 (Dll1). We confirmed the interaction between Dll1 and Acvrinp1 by pull-down experiments in vitro and in a mammalian two-hybrid system in vivo. We delimited the fourth PDZ domain of Acvrinp1 and the PDZ-binding domain of Dll1 as major interacting domains. In situ expression analyses in mouse embryos revealed that Dll1 and Acvrinp1 show partly overlapping but distinct expression patterns, for example, in the central nervous system and the vibrissae buds. Further, we found that expression of Acvrinp1 is altered in Dll1 loss-of-function mouse embryos.

Alterations of glucosylceramide-beta-glucosidase levels in the skin of patients with psoriasis vulgaris.

Hydrolysis of glucosylceramides by the enzyme glucosylceramide-beta-glucosidase (GlcCer'ase) results in ceramide, a critical component of the intercellular lamellae that mediates the epidermal permeability barrier. A disturbance of ceramide formation is supposed to influence the transepidermal water loss in common skin diseases like atopic eczema or psoriasis. The aim of this study was to investigate whether GlcCer'ase levels were altered in the skin of subjects with psoriasis vulgaris. Skin punch biopsies were taken from lesional and non-lesional psoriatic skin and GlcCer'ase was evaluated both at the RNA and at the protein level. Normal skin from surgical patients provided the baseline GlcCer'ase expression in healthy subjects. Our results show that GlcCer'ase mRNA expression was decreased in psoriatic non-lesional skin compared to normal controls in all cases. Interestingly, in lesional psoriatic skin the level of GlcCer'ase was increased compared to non-lesional skin in all cases. For the immunohistochemical analysis, we used a newly synthesized monoclonal antibody anti-human GBC (GlcCer'ase-GST fusion protein). The results confirmed that GlcCer'ase, mainly present in the upper epidermis, was decreased in psoriatic skin compared to normal control and was increased in lesional compared to non-lesional psoriatic skin. Our findings support the concept that alteration in water permeability barrier in lesional psoriatic skin can serve as a trigger for the upregulation of the expression of enzymes like GlcCer'ase with consequent stimulation of ceramide generation.

Farnesyltransferase inhibitor FTI-277 prevents autocrine growth stimulation of neuroblastoma by BDNF.

PURPOSE: Autocrine growth stimulation by IGF-II and BDNF is frequently observed in neuroblastoma. The signals of the receptors of these growth factors are transduced to the nucleus via the Ras-MAP-kinase pathway where they induce proliferation. Inactivation of Ras-proteins by farnesyltransferase inhibitors such as FTI-277 disrupts growth stimulation of ras-transformed cells. We investigated whether FTI-277 is also active against tumor cells with constitutively activated growth factor receptors but lacking ras-mutations. METHOD: We analyzed eight different neuroblastoma cell lines for the expression of BDNF and its receptor trkB. Two of these cell lines with a complete autocrine BDNF loop were treated with FTI-277, and the effects of Ras-inactivation on the signal transduction of BDNF were analyzed. RESULTS: Treatment of neuroblastoma cells with 10 microM FTI-277 for 4 days reduced the amount of membrane-bound Ras-protein to almost 50%. Activation of MAP-kinase, induction of N-myc expression, and proliferation were clearly reduced in the treated cells. In addition, we observed some cytotoxic effects of FTI-277 accompanied by morphological changes of the neuroblastoma cells and a delayed induction of apoptosis. CONCLUSION: Farnesyltransferase inhibitors are active against neuroblastoma cells but the mechanism of action is not limited to inactivation of Ras. Further investigations on the targets of FTI-277 are recommended.

Sox17-dependent gene expression and early heart and gut development in Sox17-deficient mouse embryos.

Sox17 is a transcription factor that is required for maintenance of the definitive endoderm in mouse embryos. By expression profiling of wild-type and mutant embryos and Sox17-overexpressing hepatoma cells, we identified genes with Sox17-dependent expression. Among the genes that were up-regulated in Sox17-null embryos and down-regulated by Sox17 expressing HepG2 cells is a set of genes that are expressed in the developing liver, suggesting that one function of Sox17 is the repression of liver gene expression, which is compatible with a role for Sox17 in maintaining the definitive endoderm in a progenitor state. Consistent with these findings, Sox17(-/-) cells display a diminished capacity to contribute to the definitive endoderm when transplanted into wild-type hosts. Analysis of gene ontology further revealed that many genes related to heart development were downregulated in Sox17-null embryos. This is associated with the defective development of the heart in the mutant embryos, which is accompanied by localised loss of Myocd-expressing cardiogenic progenitors and the malformation of the anterior intestinal portal.