Electron tomography reveals changes in spatial distribution of UBTF1 and UBTF2 isoforms within nucleolar components during rRNA synthesis inhibition

Leucine-Based Pseudo-Proteins (LPPs) as Promising Biomaterials: A Study of Cell-Supporting Properties

Scaffold-based systems have become essential in biomedical research, providing the possibility of building in vitro models that can better mimic tissue/organic physiology. A relatively new family of biomimetics-pseudo-proteins (PPs)-can therefore be considered especially promising in this context. Three different artificial leucine-based LPP films were tested in vitro as potential scaffolding materials. In vitro experiments were performed using two types of cells: primary mouse skin fibroblasts and a murine monocyte/macrophages cell line, RAW264.7. Cell adhesion and cell spreading were evaluated according to morphological parameters via scanning electron microscopy (SEM), and they were assessed according to actin cytoskeleton distribution, which was studied via confocal laser microscopy. Cell proliferation was evaluated via an MTT assay. Cell migration was studied using time-lapse microscopy. SEM images for both types of cells demonstrated prominent adhesion and perfect cell spreading on all three LPPs. Analyses of actin cytoskeleton organization revealed a high number of focal adhesions and prominent motility-associated structures. A certain stimulation of cell proliferation was detected in the cases of all three LPPs, and two of them promoted macrophage migration. Overall, our data suggest that the LPPs used in the study can be considered potential cell-friendly scaffolding materials.

Behavioral and molecular effects of Ubtf knockout and knockdown in mice

The UBTF E210K neuroregression syndrome is caused by de novo dominant mutations in UBTF (NM_014233.3:c.628G > A, p.Glu210Lys). In humans, onset is typically at 2.5 to 3 years and characterized by slow progression of global motor, cognitive and behavioral dysfunction. Other potentially pathogenic UBTF variants have been reported in humans with severe neurological disease and it remains undetermined if the UBTF E210K mutation operates via gain- and/or loss-of-function. Here we examine the behavioral, cognitive, motor, and molecular effects of Ubtf knockout and knockdown in mice as a means of gauging the role of loss-of-function in humans. Ubtf+/- mice show progression of behavioral (dominance tube), cognitive (cross maze), and mild motor abnormalities from 3 to 18 months. At 18 months, Ubtf+/- mice had more slips on a raised 9-mm round beam task, shorter latencies to fall on the accelerated rotarod, reduced open field vertical and jump counts, and significant deficits in spatial learning and memory. Via crosses to Nestin-Cre (NesCre) mice we found that homozygous Ubtf deletion limited to the central nervous system was embryonic lethal. Tamoxifen-induced homozygous knockdown of Ubtf in adult mice with the Cre-ERT2 system was associated with precipitous deterioration in neurological functioning. At the molecular level, 18-month-old Ubtf+/- mice showed mild increases in cerebellar 53BP1 immunoreactivity. These findings show that UBTF is essential for embryogenesis and survival in adults, and the deleterious effects of UBTF haploinsufficiency progress with age. Loss-of-function mechanisms may contribute, in part, to the human UBTF E210K neuroregression syndrome.

Visualization of Chromatin in the Yeast Nucleus and Nucleolus Using Hyperosmotic Shock

Unlike in most eukaryotic cells, the genetic information of budding yeast in the exponential growth phase is only present in the form of decondensed chromatin, a configuration that does not allow its visualization in cell nuclei conventionally prepared for transmission electron microscopy. In this work, we studied the distribution of chromatin and its relationships to the nucleolus using different cytochemical and immunocytological approaches applied to yeast cells subjected to hyperosmotic shock. Our results show that osmotic shock induces the formation of heterochromatin patches in the nucleoplasm and intranucleolar regions of the yeast nucleus. In the nucleolus, we further revealed the presence of osmotic shock-resistant DNA in the fibrillar cords which, in places, take on a pinnate appearance reminiscent of ribosomal genes in active transcription as observed after molecular spreading ("Christmas trees"). We also identified chromatin-associated granules whose size, composition and behaviour after osmotic shock are reminiscent of that of mammalian perichromatin granules. Altogether, these data reveal that it is possible to visualize heterochromatin in yeast and suggest that the yeast nucleus displays a less-effective compartmentalized organization than that of mammals.

Trnp1 organizes diverse nuclear membrane-less compartments in neural stem cells

TMF1‐regulated nuclear protein 1 (Trnp1) has been shown to exert potent roles in neural development affecting neural stem cell self‐renewal and brain folding, but its molecular function in the nucleus is still unknown. Here, we show that Trnp1 is a low complexity protein with the capacity to phase separate. Trnp1 interacts with factors located in several nuclear membrane‐less organelles, the nucleolus, nuclear speckles, and condensed chromatin. Importantly, Trnp1 co‐regulates the architecture and function of these nuclear compartments in vitro and in the developing brain in vivo. Deletion of a highly conserved region in the N‐terminal intrinsic disordered region abolishes the capacity of Trnp1 to regulate nucleoli and heterochromatin size, proliferation, and M‐phase length; decreases the capacity to phase separate; and abrogates most of Trnp1 protein interactions. Thus, we identified Trnp1 as a novel regulator of several nuclear membrane‐less compartments, a function important to maintain cells in a self‐renewing proliferative state.