The lateral ventricle (LV) is flanked by the subventricular zone (SVZ), a neural stem cell (NSC) niche rich in extrinsic growth factors regulating NSC maintenance, proliferation, and neuronal differentiation. Dysregulation of the SVZ niche causes LV expansion, a condition known as hydrocephalus; however, the underlying pathological mechanisms are unclear. We show that deficiency of the proteoglycan Tsukushi (TSK) in ependymal cells at the LV surface and in the cerebrospinal fluid results in hydrocephalus with neurodevelopmental disorder-like symptoms in mice. These symptoms are accompanied by altered differentiation and survival of the NSC lineage, disrupted ependymal structure, and dysregulated Wnt signaling. Multiple TSK variants found in patients with hydrocephalus exhibit reduced physiological activity in mice in vivo and in vitro. Administration of wild-type TSK protein or Wnt antagonists, but not of hydrocephalus-related TSK variants, in the LV of TSK knockout mice prevented hydrocephalus and preserved SVZ neurogenesis. These observations suggest that TSK plays a crucial role as a niche molecule modulating the fate of SVZ NSCs and point to TSK as a candidate for the diagnosis and therapy of hydrocephalus.

Tsukushi (TSK) is a small signaling molecule which takes part in different developmental processes of multiple vertebrate organisms. The diverse activity of TSK depends on its ability to bind various intermediate molecules from different major signaling pathways. Interactions of TSK with BMP, FGF, TGF-β and Wnt pathways have already been confirmed. In this review, we will introduce the latest information regarding the involvement of TSK in developmental events. We suggest a fine tuning role for TSK in multiple signaling cascades. Also, we recommend further studies on the developmental role of TSK to fully reveal its potential.

Secreted proteoglycan molecule Tsukushi (TSK) regulates various developmental processes, such as early body patterning and neural plate formation by interacting with major signaling pathways like Wnt, BMP, Notch etc. In central nervous system, TSK inhibits Wnt signaling to control chick retinal development. It also plays important roles for axon guidance and anterior commissure formation in mouse brain. In the present study, we investigated the role of TSK for the development and proper functioning of mouse hippocampus. We found that TSK expression is prominent at hippocampal regions of early postnatal mouse until postnatal day 15 and gradually declines at later stages. Hippocampal dimensions are affected in TSK knockout mice (TSK‐KO) as shown by reduced size of hippocampus and dentate gyrus (DG). Interestingly, neural stem cell (NSC) density at the neural niche of DG was higher in TSK‐KO compared with wild‐type. The ratio of proliferating NSCs as well as the rate of overall cell proliferation was also higher in TSK‐KO hippocampus. Our in vitro study also suggests an increased number of neural stem/progenitor cells residing in TSK‐KO hippocampus. Finally, we found that the terminal differentiation of NSCs in TSK‐KO was disturbed as the differentiation to neuronal cell lineage was increased while the percentages of astrocytes and oligodendrocytes were decreased. Overall, our study establishes the involvement of TSK in hippocampal development, NSC maintenance and terminal differentiation at perinatal stages.

Extracellular molecules coordinate the multiple signaling pathways spatiotemporally to exchange information between cells during development. Understanding the regulation of these signal molecule-dependent pathways elucidates the mechanism of intercellular crosstalks. CCN2/CTGF is one of the CCN family members that binds BMP2, fibronectin, aggrecan, FGFR2 - regulating cartilage and bone formation, angiogenesis, wound repair etc. Tsukushi (TSK), which belongs to the Small Leucine-Rich Proteoglycan (SLRP) family, binds nodal/Vg1/TGF-β1, BMP4/chordin, Delta, FGF8, Frizzled4, and is involved in the early body formation, bone growth, wound healing, retinal stem cell regulation etc. These two secreted molecules are expressed in similar tissues and involved in several biological events by functioning as extracellular signaling modulators. Here, we examine the molecular interaction between CCN2 and TSK biochemically. Co-precipitation assay and Surface Plasmon Resonance measurement showed their direct binding with the Kd value 15.3 nM. Further, the Solid-phase Binding Assay indicated that TSK binds to IGFBP and CT domains of CCN2. Our data suggest that CCN2 and TSK exert their function together in the body formation.

Although ribosomes are generally known to be a translational machinery, some ribosomal proteins also have accessory functions involving early development and differentiation. Previously, we reported that ribosome incorporation into human dermal fibroblasts generated embryoid body-like cell clusters, altered cellular fate, and differentiated into cells of all 3 germ layers. However, the molecular phenomena induced by ribosome incorporation in the cell remained unknown. Here, we demonstrate that ribosome incorporation into human breast cancer cell MCF7 leads to ribosome-induced cell clusters (RICs) formation accompanying with epithelial-mesenchymal transition (EMT)-like gene expression. Following ribosome incorporation, MCF7 cells cease proliferation, which is caused by inhibition of cell cycle transition from G0 to G1 phase. Further, MCF7 RICs show induced expression of EMT markers, TGF-β1 and Snail along with autophagy markers and tumor suppressor gene p53. These findings indicate that the incorporation of ribosome into cancer cells induces an EMT-like phenomenon and changes the cancer cell characteristics.