A mouse homologue of Strawberry Notch is transcriptionally regulated by Reelin signal

Notch and Hippo signaling converge on Strawberry Notch 1 (Sbno1) to synergistically activate Cdx2 during specification of the trophectoderm

The first binary cell fate decision occurs at the morula stage and gives rise to two distinct types of cells that constitute the trophectoderm (TE) and inner cell mass (ICM). The cell fate determinant, Cdx2, is induced in TE cells and plays an essential role in their differentiation and maintenance. Notch and Hippo signaling cascades are assumed to converge onto regulatory elements of Cdx2, however, the underlying molecular mechanisms are largely unknown. Here, we show involvement of Strawberry Notch1 (Sbno1), a novel chromatin factor of the helicase superfamily 2, during preimplantation development. Sbno1 knockout embryos die at the preimplantation stage without forming a blastocoel, and Cdx2 is not turned on even though both Yap and Tead4 reside normally in nuclei. Accordingly, Sbno1 acts on the trophectoderm-enhancer (TEE) of Cdx2, ensuring its robust and synergistic activation by the Yap/Tead4 and NICD/Rbpj complexes. Interestingly, this synergism is enhanced when cells are mechanically stretched, which might reflect that TE cells are continuously stretched by the expanding ICM and blastocoel cavity. In addition, the histone chaperone, FACT (FAcilitates Chromatin Transcription) physically interacts with Sbno1. Our data provide new evidence on TE specification, highlighting unexpected but essential functions of the highly conserved chromatin factor, Sbno1.

Strawberry notch homolog 2 is a novel inflammatory response factor predominantly but not exclusively expressed by astrocytes in the central nervous system

Interleukin‐6 (IL‐6) participates in the host response to injury and infection in the central nervous system (CNS). We identified strawberry notch homolog 2 (Sbno2) as an IL‐6‐stimulated gene in murine astrocytes. Sbno2 is a mouse homolog of the sno gene in Drosophila but little is known about the regulation or function of the mammalian gene. Here we examined the regulation of the Sbno2 gene in astrocytes in vitro and in the murine CNS following systemic endotoxin administration. In murine and human cultured astrocytes, Sbno2 gene expression was significantly upregulated in a dose‐ and time‐dependent fashion by hyper‐IL‐6 (IL‐6 + soluble IL‐6 receptor). The level of Sbno2 mRNA was also upregulated significantly in murine astrocytes by other glycoprotein130 cytokine‐family members and the pro‐inflammatory cytokines interleukin‐1 beta and tumor necrosis factor alpha. These changes were reflected by corresponding alterations in the level of the SBNO2 protein. Inhibiting protein synthesis resulted in higher Sbno2 mRNA and did not abolish the upregulation of Sbno2 mRNA mediated by hyper‐IL‐6. Inhibition of transcription led to a rapid reduction in hyper‐IL‐6‐induced Sbno2 mRNA in astrocytes suggesting that the Sbno2 mRNA is quite unstable. Following intra‐peritoneal lipopolysaccharide injection in mice, Sbno2 mRNA levels in the brain were significantly increased. Cellular localization studies revealed that this increase in Sbno2 mRNA occurred predominantly in astrocytes and in the choroid plexus and in some microglia, endothelial cells, and neurons. These findings are consistent with SBNO2 functioning as an acute inflammatory response gene in astrocytes as well as other cells in the CNS. GLIA 2015;63:1738–1752

Gene expression profiling in rodent models for schizophrenia

The complex neurodevelopmental disorder schizophrenia is thought to be induced by an interaction between predisposing genes and environmental stressors. In order to get a better insight into the aetiology of this complex disorder, animal models have been developed. In this review, we summarize mRNA expression profiling studies on neurodevelopmental, pharmacological and genetic animal models for schizophrenia. We discuss parallels and contradictions among these studies, and propose strategies for future research.

Expression of strawberry notch family genes during zebrafish embryogenesis

Our previous study suggested a possible role for Sbno1, a mouse homologue of strawberry notch gene during brain development. In this report, we cloned the zebrafish homologues of sbno, and examined their expression pattern during embryogenesis by whole-mount in situ hybridization. Zebrafish have three sbno genes: one Sbno1 homologue and two Sbno2 homologues, sbno2a and sbno2b. We observed that the expression of sbno1 and sbno2a was initially ubiquitous and gradually became predominant in the central nervous system as development progressed. The expression of sbno2b was observed in non-neural tissues in contrast to the other two genes. sbno1 and sbno2a exhibited higher expression in distinct regions within the nervous system of pharyngula-stage embryos, suggesting possible differing roles for sbno1 and sbno2a during later stages of embryogenesis. Together, the observed gene expression patterns suggest an important role of sbno-family genes during development of the vertebrate central nervous system.

Developmental anatomy of reeler mutant mouse

The reeler mouse is one of the most famous spontaneously occurring mutants in the research field of neuroscience, and this mutant has been used as a model animal to understand mammalian brain development. The classical observations emphasized that laminar structures of the reeler brain are highly disrupted. Molecular cloning of Reelin, the gene responsible for reeler mutant provided insights into biochemistry of Reelin signal, and some models had been proposed to explain the function of Reelin signal in brain development. However, recent reports of reeler found that non-laminated structures in the central nervous system are also affected by the mutation, making function of Reelin signal more controversial. In this review, we summarized reported morphological and histological abnormalities throughout the central nervous system of the reeler comparing to those of the normal mouse. Based on this overview of the reeler abnormalities, we discuss possible function of Reelin signal in the neuronal migration and other morphological events in mouse development.

Neuronal migration and neurodegeneration: 2 sides of the same coin

The human genome contains only about double the number of genes in comparison to the fruit fly. This necessitates efficient recurrent usage of the same molecular components to participate in different processes. When the same proteins are used for different signaling pathways, it may be conceivable that if they go awry the phenotypic consequences may vary to a great extent. The involvement of amyloid beta precursor protein, Presenilin-1, and Tau in the pathogenesis of Alzheimer's disease is well established. Here we are highlighting a second facet of their function, their participation in developmental and adult neuronal migration. We propose that the prevalent and early Anosmia found in Alzheimer's patients may be due in part to malfunctioning of the above-mentioned proteins.

Interaction between Reelin and Notch signaling regulates neuronal migration in the cerebral cortex

Neuronal migration is a fundamental component of brain development whose failure is associated with various neurological and psychiatric disorders. Reelin is essential for the stereotypical inside-out sequential lamination of the neocortex, but the molecular mechanisms of its action still remain unclear. Here we show that regulation of Notch activity plays an important part in Reelin-signal-dependent neuronal migration. We found that Reelin-deficient mice have reduced levels of the cleaved form of Notch intracellular domain (Notch ICD) and that loss of Notch signaling in migrating neurons results in migration and morphology defects. Further, overexpression of Notch ICD mitigates the laminar and morphological abnormalities of migrating neurons in Reeler. Finally, our in vitro biochemical studies show that Reelin signaling inhibits Notch ICD degradation via Dab1. Together, our results indicate that neuronal migration in the developing cerebral cortex requires a Reelin-Notch interaction.