Wnt signaling polarizes cortical actin polymerization to increase daughter cell asymmetry

Multifaceted regulation of asymmetric cell division by the actin cytoskeleton

Asymmetric cell division (ACD) is essential for generating cell diversity in multicellular eukaryotes, yet the underlying mechanisms remain largely unresolved. Well-established models of ACD, such as microtubule-based spindle displacement in Caenorhabditis elegans embryos and preprophase band assembly in plants provide valuable insights but fail to fully explain asymmetry establishment in others. In this article, we discuss how actin-dependent mechanisms govern ACD in model systems, highlighting emerging commonalities and differences. Given its broad impact, the actin cytoskeleton may play a more significant role in ACD than currently recognized, serving as a fundamental component during organismal development across kingdoms.

Sodium arsenite induces islets β-cells apoptosis and dysfunction via SET-Rac1-mediated cytoskeleton disturbance

Sodium arsenite (NaAsO2), the most common form of inorganic arsenic prevalent in the environment, has been closely linked to islet β-cell dysfunction, a critical pathological hallmark of type 2 diabetes (T2D). Even though apoptosis plays a pivotal role in arsenic-induced islet β-cell dysfunction, the explicit underlying mechanisms remain elusive. Here, we have identified that the SET-Rac1 signaling pathway is instrumental in the apoptosis and dysfunction of islet β-cells induced by NaAsO2. During NaAsO2-induced islet β-cell apoptosis and dysfunction, our observations indicated downregulation of SET (almost 0.5-fold) and upregulation of Rac1 (0.5-fold). Notably, overexpression of SET or inhibition of Rac1 substantially mitigated the apoptosis of islet β-cells and ameliorated the impaired insulin secretion (increased from 0.1 ng/ml to 0.2 ng/ml) caused by NaAsO2 exposure. In addition, we detected cytoskeletal disorganization following NaAsO2 treatment, characterized by elevated Cofilin-1 protein expression (approximately 2.5-fold) and disrupted cytoskeleton arrangement. Significantly, overexpression of SET or deletion of Rac1 rectified the NaAsO2-induced cytoskeletal abnormalities, as evidenced by the reduced Cofilin-1 expression and enhanced F-actin fluorescence. Our research delineates that NaAsO2 triggers apoptosis and functional impairment of islet β-cells through cytoskeletal rearrangement mediated by the SET-Rac1 pathway. This discovery could provide novel insights into therapeutic strategies for T2D provoked by environmental toxicants.

LSD1 controls a nuclear checkpoint in Wnt/β-Catenin signaling to regulate muscle stem cell self-renewal

The Wnt/β-Catenin pathway plays a key role in cell fate determination during development and in adult tissue regeneration by stem cells. These processes involve profound gene expression and epigenome remodeling and linking Wnt/β-Catenin signaling to chromatin modifications has been a challenge over the past decades. Functional studies of the lysine demethylase LSD1/KDM1A converge to indicate that this epigenetic regulator is a key regulator of cell fate, although the extracellular cues controlling LSD1 action remain largely unknown. Here we show that β-Catenin is a substrate of LSD1. Demethylation by LSD1 prevents β-Catenin degradation thereby maintaining its nuclear levels. Consistently, in absence of LSD1, β-Catenin transcriptional activity is reduced in both MuSCs and ESCs. Moreover, inactivation of LSD1 in mouse muscle stem cells and embryonic stem cells shows that LSD1 promotes mitotic spindle orientation via β-Catenin protein stabilization. Altogether, by inscribing LSD1 and β-Catenin in the same molecular cascade linking extracellular factors to gene expression, our results provide a mechanistic explanation to the similarity of action of canonical Wnt/β-Catenin signaling and LSD1 on stem cell fate.

Proteomics reveals the underlying mechanism by which the first uneven division affects embryonic development in pig

One of the most typical abnormal cleavage patterns during early embryonic development is uneven division, but the first uneven division of pig zygote is common. Uneven division results in different daughter cell sizes and an uneven distribution of organelles such as lipid droplet, mitochondria, but the developmental capacity of daughter cells and proteomic changes of daughter cells are still unclear. Therefore, the developmental ability and proteomic quantification were investigated on blastomeres from even division (ED) or uneven division (UD) embryos at 2-cell stage in the present study. Firstly, the developmental ability was affected by the blastomeric size, when compared with medium blastomeres (MBs), the large blastomeres (LBs) with the higher cleavage rate but the small blastomeres (SBs) with the lower rate was observed. Subsequently, proteomic analysis was performed on blastomeres of LBs, MBs and SBs, a total of 109 DEPs were detected, which were involved in protein metabolism and processing, energy metabolism and ribosome. In particular, DEPs in LBs vs. SBs were focused on RNA binding and actin cytoskeletal tissue. Two protein-dense networks associated with RNA binding and cytoskeleton were revealed by further protein-protein interaction (PPI) analysis of DEPs in LBs vs. SBs, that DDX1 related to RNA binding and ACTB related to cytoskeleton were confirmed in UD embryos. Therefore, a briefly information of DEPs in blastomeres of 2-cell stage pig embryos was described in the present study, and it further confirmed that the formation of uneven division of the first cell cycle of pig embryos might be controlled by the cytoskeleton; the developmental capacity of daughter cells might be affected by the energy metabolism, RNA binding and ribosome, and further account for the developmental potential of the whole embryo.

Polarized SCAR and the Arp2/3 complex regulate apical cortical remodeling in asymmetrically dividing neuroblasts

Although the formin-nucleated actomyosin cortex has been shown to drive the changes in cell shape that accompany animal cell division in both symmetric and asymmetric cell divisions, the mitotic role of cortical Arp2/3-nucleated actin networks remain unclear. Here using asymmetrically dividing Drosophila neural stem cells as a model system, we identify a pool of membrane protrusions that form at the apical cortex of neuroblasts as they enter mitosis. Strikingly, these apically localized protrusions are enriched in SCAR, and depend on SCAR and Arp2/3 complexes for their formation. Because compromising SCAR or the Arp2/3 complex delays the apical clearance of Myosin II at the onset of anaphase and induces cortical instability at cytokinesis, these data point to a role for an apical branched actin filament network in fine-tuning the actomyosin cortex to enable the precise control of cell shape changes during an asymmetric cell division.