Microtubules deform the nucleus and force chromatin reorganization during early differentiation of human hematopoietic stem cells

Abstract

Hematopoietic stem cells (HSC) can differentiate into all hematopoietic lineages to support hematopoiesis. Cells from the myeloid and lymphoid lineages fulfill distinct functions with specific shapes and intra-cellular architectures. The role of cytokines in the regulation of HSC differentiation has been intensively studied but our understanding of the potential contribution of inner cell architecture is relatively poor. Here we show that large invaginations are generated by microtubule constraints on the swelling nucleus of human HSCs during early commitment toward the myeloid lineage. These invaginations are associated with chromatin reorganization, local loss of H3K9 trimethylation and changes in expression of specific hematopoietic genes. This establishes the role of microtubules in defining the unique lobulated nuclear shape observed in myeloid progenitor cells and suggests that this shape is important to establish the gene expression profile specific to this hematopoietic lineage. It opens new perspectives on the implications of microtubule-generated forces, in the early specification of the myeloid lineage.

Arrhythmogenic Cardiomyopathy Is a Multicellular Disease Affecting Cardiac and Bone Marrow Mesenchymal Stromal Cells

“…In light of the well-accepted role played by the microtubule and microfilament network in the regulation of cell proliferation and migration [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], the finding of altered cytoskeletal architecture in AC cells prompted us to verify whether the proliferative and migratory capacity of MSCs, harboring the Dsg2 -variant, differed from controls. We thus estimated in vitro the proliferative index of AC vs. control MSCs, of either cardiac or BM origin, by performing a BrdU incorporation assay and measured the fractions of cells immunoreactive toward an anti-BrdU antibody via flow cytometry.…”

“…In our experiments, DSG2 downregulation was associated, in both cardiac- and BM-MSCs from Dsg2 mut/mut mice, with profound alterations in the organization of actin filaments with the coexistence of cell areas occupied by actin ‘puncta’ and thick actin filament bundles beneath the cell membrane. In parallel, we also observed profound changes in the organization of microtubules, which have been shown to regulate cell motility and shape [ 27 ] and differentiation properties [ 28 , 29 ]. That such alterations were detected in vitro in two different MSC sub-populations and in a cell culture system free from context dependent factors strongly supports a direct role of AC-linked Dsg2 variant in influencing the MSC phenotype.…”

Modeling of Cell Nuclear Mechanics: Classes, Components, and Applications

“…Additionally, Arp2/3-driven actin polymerization has been shown to disrupt the nuclear lamina and facilitate constricted migration [54]. The cytoskeleton also serves an antagonistic rule as both actin and microtubules can deform the nucleus [55][56][57]. The literature regarding actin and the actual mechanical properties of the nucleus are seemingly conflicting, likely due to extension-versus compression-based force measurements and the aforementioned antagonistic behavior.…”

Nuclear mechanotransduction in stem cells

“…The polymerization state of actin, also influenced by contractility, controls serum response factor (SRF) signaling, which at least in some cells plays a role in cell signaling [7,8]. Moreover, the cytoskeleton also propagates mechanical stresses into the nucleus, affecting its molecular composition and physical arrangement [9,10], the structural organization and apico-basal polarity of the nuclear lamina [11], and molecular traffic across the nuclear envelope [12,13]. This relay of mechanical stress, called nuclear mechanotransduction [14,15], could occur in several ways, and involves several categories of macromolecular complexes: cytoskeletal-nucleus connections; the nuclear envelope; and chromatin.…”