Cell signaling: moving to a Wnt-Rap

Intellectual disability syndrome associated with a homozygous founder variant in SGSM3 in Ashkenazi Jews

BACKGROUND

Neurodevelopmental disorders (NDDs) impact both the development and functioning of the brain and exhibit clinical and genetic variability. RAP and RAB proteins, belonging to the RAS superfamily, are identified as established contributors to NDDs. However, the involvement of SGSM (small G protein signalling modulator), another member of the RAS family, in NDDs has not been previously documented.

METHODS

Proband-only or trio exome sequencing was performed on DNA samples obtained from affected individuals and available family members. The variant prioritisation process focused on identifying rare deleterious variants. International collaboration aided in the identification of additional affected individuals.

RESULTS

We identified 13 patients from 8 families of Ashkenazi Jewish origin who all carried the same homozygous frameshift variant in SGSM3 gene. The variant was predicted to cause a loss of function, potentially leading to impaired protein structure or function. The variant co-segregated with the disease in all available family members. The affected individuals displayed mild global developmental delay and mild to moderate intellectual disability. Additional prevalent phenotypes observed included hypotonia, behavioural challenges and short stature.

CONCLUSIONS

An Ashkenazi Jewish homozygous founder variant in SGSM3 was discovered in individuals with NDDs and short stature. This finding establishes a connection between another member of the RAS family and NDDs. Additional research is needed to uncover the specific molecular mechanisms by which SGSM3 influences neurodevelopmental processes and the regulation of growth.

Tideglusib enhances odontogenic differentiation in human dental pulp stem cells in vitro

AIM

Tideglusib is a small molecule agonist of the canonical Wnt pathway. The present study investigated the influence of Tideglusib on human dental pulp stem cell (hDPSC) proliferation, apoptosis, migration and odonto/osteogenic differentiation.

METHODOLOGY

hDPSCs were treated with 50, 100 nM or 200 nM Tideglusib. β-catenin accumulation was detected by immunofluorescence staining. Colony-forming unit ability was assessed by staining with Coomassie blue. Cell cycle progression and cell apoptosis were investigated using flow cytometry. Cell migration was examined using an in vitro wound-healing assay. Osteogenic differentiation was examined using alkaline phosphatase (ALP) staining, alizarin red S staining and osteogenic-related gene expression. The gene expression profile was examined using a high-throughput RNA sequencing technique. All experiments were repeated using cells derived from at least four different donors (n = 4). The Mann-Whitney U-test was used to identify significant differences between two independent group comparisons. For three or more group comparisons, statistical differences were assessed using the Kruskal-Wallis test followed by pairwise comparison. The significance level was set at 5% (p < .05).

RESULTS

Tideglusib activated the Wnt signalling pathway in hDPSCs as demonstrated by an increase in cytoplasmic β-catenin accumulation and nuclear translocation. Tideglusib did not affect hDPSC proliferation, cell cycle progression, cell apoptosis or cell migration. In contrast, 50 and 100 nM Tideglusib significantly enhanced mineralization and osteogenic marker gene expression (RUNX2, ALP, BMP2 and DSPP; p < .05).

CONCLUSIONS

Tideglusib enhanced the odonto/osteogenic differentiation of hDPSCs. Therefore, incorporating this bioactive molecule in a pulp-capping material could be a promising strategy to promote dentine repair.

Potential of casein kinase I in digestive cancer screening

Casein kinase I is a group of ubiquitous Serine/Threonine kinases that have been implicated in both normal cellular functions and several pathological conditions including Alzheimer’s disease and cancer. Recent findings in colon and pancreatic cancer have brought tremendous attention to these molecules as potential therapeutic targets in treatment of digestive cancers. In this review, we summarize up to date what is known about this family of kinases and their involvement in carcinogenesis and other pathological conditions. Our emphasis is on their implications in digestive cancers and their potential for cancer screening and therapy.

Non-redundant roles for Profilin2 and Profilin1 during vertebrate gastrulation

Gastrulation is a critical morphogenetic event during vertebrate embryogenesis, and it is comprised of directional cell movement resulting from the polarization and reorganization of the actin cytoskeleton. The non-canonical Wnt signaling pathway has emerged as a key regulator of gastrulation. However, the molecular mechanisms by which the Wnt pathway mediates changes to the cellular actin cytoskeleton remains poorly defined. We had previously identified the Formin protein Daam1 and an effector molecule XProfilin1 as links for Wnt-mediated cytoskeletal changes during gastrulation. We report here the identification of XProfilin2 as a non-redundant and distinct effector of Daam1 for gastrulation. XProfilin2 interacts with FH1 domain of Daam1 and temporally interacts with Daam1 during gastrulation. In the Xenopus embryo, XProfilin2 is temporally expressed throughout embryogenesis and it is spatially expressed in cells undergoing morphogenetic movement during gastrulation. While we have previously shown XProfilin1 regulates blastopore closure, overexpression or depletion of XProfilin2 specifically affects convergent extension movement independent of mesodermal specification. Specifically, we show that XProfilin2 modulates cell polarization and axial alignment of mesodermal cells undergoing gastrulation independent of XProfilin1. Together, our studies demonstrate that XProfilin2 and XProfilin1 are non-redundant effectors for Daam1 for non-canonical Wnt signaling and that they regulate distinct functions during vertebrate gastrulation.

Are small GTPases signal hubs in sugar-mediated induction of fructan biosynthesis?

External sugar initiates biosynthesis of the reserve carbohydrate fructan, but the molecular processes mediating this response remain obscure. Previously it was shown that a phosphatase and a general kinase inhibitor hamper fructan accumulation. We use various phosphorylation inhibitors both in barley and in Arabidopsis and show that the expression of fructan biosynthetic genes is dependent on PP2A and different kinases such as Tyr-kinases and PI3-kinases. To further characterize the phosphorylation events involved, comprehensive analysis of kinase activities in the cell was performed using a PepChip, an array of >1000 kinase consensus substrate peptide substrates spotted on a chip. Comparison of kinase activities in sugar-stimulated and mock(sorbitol)-treated Arabidopsis demonstrates the altered phosphorylation of many consensus substrates and documents the differences in plant kinase activity upon sucrose feeding. The different phosphorylation profiles obtained are consistent with sugar-mediated alterations in Tyr phosphorylation, cell cycling, and phosphoinositide signaling, and indicate cytoskeletal rearrangements. The results lead us to infer a central role for small GTPases in sugar signaling.

Wnt signal transduction pathways

The Wnt signaling pathway is an ancient and evolutionarily conserved pathway that regulates crucial aspects of cell fate determination, cell migration, cell polarity, neural patterning and organogenesis during embryonic development. The Wnts are secreted glycoproteins and comprise a large family of nineteen proteins in humans hinting to a daunting complexity of signaling regulation, function and biological output. To date major signaling branches downstream of the Fz receptor have been identified including a canonical or Wnt/beta-catenin dependent pathway and the non-canonical or beta-catenin-independent pathway which can be further divided into the Planar Cell Polarity and the Wnt/Ca(2+) pathways, and these branches are being actively dissected at the molecular and biochemical levels. In this review, we will summarize the most recent advances in our understanding of these Wnt signaling pathways and the role of these pathways in regulating key events during embryonic patterning and morphogenesis.