Biology subjects

Ott, C.

Publications and source records attributed to Ott, C..

3 recordsLinked to original sources

bioRxiv2021

Oligodendrocyte precursor cells prune axons in the mouse neocortex

Neurons in the developing brain undergo extensive structural refinement as nascent circuits adopt their mature form1. This transformation is facilitated by the engulfment and degradation of excess axonal branches and inappropriate synapses by surrounding glial cells, including microglia and astrocytes2,3. However, the small size of phagocytic organelles and the complex, highly ramified morphology of glia has made it difficult to determine the contribution of these and other glial cell types to this process. Here, we used large scale, serial electron microscopy (ssEM) with computational volume segmentation to reconstruct the complete 3D morphologies of distinct glial types in the mouse visual cortex. Unexpectedly, we discovered that the fine processes of oligodendrocyte precursor cells (OPCs), a population of abundant, highly dynamic glial progenitors4, frequently surrounded terminal axon branches and included numerous phagolysosomes (PLs) containing fragments of axons and presynaptic terminals. Single- nucleus RNA sequencing indicated that cortical OPCs express key phagocytic genes, as well as neuronal transcripts, consistent with active axonal engulfment. PLs were ten times more abundant in OPCs than in microglia in P36 mice, and declined with age and lineage progression, suggesting that OPCs contribute very substantially to refinement of neuronal circuits during later phases of cortical development.

neuroscience↗

bioRxiv2021

Inability to switch from ARID1A-BAF to ARID1B-BAF impairs exit from pluripotency and commitment towards neural crest differentiation in ARID1B-related neurodevelopmental disorders

The BAF complex modulates chromatin accessibility. Specific BAF configurations have functional consequences, and subunit switches are essential for cell differentiation. ARID1B and its paralog ARID1A encode for mutually exclusive BAF subunits. De novo ARID1B haploinsufficient mutations cause a neurodevelopmental disorder spectrum, including Coffin-Siris syndrome, which is characterized by neurological and craniofacial features. Here, we reprogrammed ARID1B+/- Coffin-Siris patient-derived skin fibroblasts into iPSCs and modeled cranial neural crest cell (CNCC) formation. We discovered that ARID1B is active only during the first stage of this process, coinciding with neuroectoderm specification, where it is part of a lineage-specific BAF configuration (ARID1B-BAF), which includes SMARCA4 and nine additional subunits. ARID1B-BAF acts as a gatekeeper, ensuring exit from pluripotency and lineage commitment, by attenuating NANOG, SOX2 and thousands of enhancers directly regulated by these two pluripotency factors at the iPSC stage. In iPSCs, these enhancers are maintained active by an ARID1A-containing BAF. At the onset of differentiation, cells transition from ARID1A-BAF to ARID1B-BAF, eliciting attenuation of the NANOG/SOX2 networks, and triggering pluripotency exit. Coffin-Siris patient cells fail to perform the ARID1A/ARID1B switch and maintain ARID1A-BAF at pluripotency enhancers throughout all stages of CNCC formation. This leads to a persistent and aberrant SOX2 and NANOG activity, which impairs CNCC formation. In fact, despite showing the typical neural crest signature (TFAP2A+, SOX9+), ARID1B-haploinsufficient CNCCs are also NANOG/OCT4-positive, in stark contrast with the ARID1B-wt CNCCs, which are NANOG/OCT4-negative. These findings suggest a connection between ARID1B mutations, neuroectoderm formation, and a pathogenic mechanism for Coffin-Siris syndrome.

genomics↗

bioRxiv2020

Mesenchyme modulates three-dimensional, collective cell migration of liver cells in vitro - a role for TGFβ pathway

Three dimensional (3D) collective cell migration (CCM) is critical for improving liver cell therapies, eliciting mechanisms of liver disease, and modeling human liver development/ organogenesis. Here, we modeled liver organogenesis to induce 3D CCM and improve existing models. The liver diverticulum, normally surrounded by septum transversum mesenchyme (STM) at E8.5, was modeled with a miniature liver spheroid surrounded by mesenchymal cells and matrix. In mixed spheroid models with both liver and uniquely MRC5 (fetal lung) fibroblasts, we observed co-migration of cells, and a significant increase in length and number of liver spheroid protrusions, and this was highly sensitive to TGFB1 stimulation. To understand paracrine effects between MRC-5 cells and liver, we performed conditioned medium (M-CM) experiments. Interestingly, the addition of M-CM increased liver 3D CCM, with thin, 3D, dose-dependent branching morphogenesis, an upregulation of Twist1, and a sensitivity to a broad TGFB inhibitor. To test the effects of cell-cell interactions of 3D CCM, the STM was modeled with a spheroid of MRC-5 cells, and we performed co-spheroid culture of liver with MRC-5. We observed a complex morphogenesis, whereby thin, linear, 3D liver cell strands attach to the MRC-5 spheroid, anchor, and thicken to form permanent and thick anchoring contacts between the two spheroids. We also observed spheroid fusion, a form of interstitial migration. In conclusion, we present several novel cultivation systems that induce distinct features of 3D CCM, as judged by the presence of branching, linearity, thickness, and interstitial migration. These methodologies will greatly improve our molecular, cellular, and tissue-scale understanding of liver organogenesis, liver diseases, and liver cell therapy, and will serve as a tool to bridge conventional 2D studies and preclinical in vivo studies.

cell biology↗