Sculpting the nucleus with dynamic microtubules

Interphase microtubules in nuclear organization and genome maintenance

Microtubules are major cytoskeletal components mediating fundamental cellular processes, including cell division. Recent evidence suggests that microtubules also regulate the nucleus during the cell cycle's interphase stage. Deciphering such roles of microtubules should uncover direct crosstalk between the nucleus and cytoplasm, impacting genome function and organismal health. Here, we review emerging roles for microtubules in interphase genome regulation. We explore how microtubules exert cytoplasmic forces on the nucleus or transport molecular cargo, including DNA, into or within the nucleus. We also describe how microtubules perform these functions by establishing transient or stable connections with nuclear envelope elements. Lastly, we discuss how the regulation of the nucleus by microtubules impacts genome organization and repair. Together, the literature indicates that interphase microtubules are critical regulators of nuclear structure and genome stability.

Mechanotranduction Pathways in the Regulation of Mitochondrial Homeostasis in Cardiomyocytes

Mitochondria are one of the most important organelles in cardiomyocytes. Mitochondrial homeostasis is necessary for the maintenance of normal heart function. Mitochondria perform four major biological processes in cardiomyocytes: mitochondrial dynamics, metabolic regulation, Ca²⁺ handling, and redox generation. Additionally, the cardiovascular system is quite sensitive in responding to changes in mechanical stress from internal and external environments. Several mechanotransduction pathways are involved in regulating the physiological and pathophysiological status of cardiomyocytes. Typically, the extracellular matrix generates a stress-loading gradient, which can be sensed by sensors located in cellular membranes, including biophysical and biochemical sensors. In subsequent stages, stress stimulation would regulate the transcription of mitochondrial related genes through intracellular transduction pathways. Emerging evidence reveals that mechanotransduction pathways have greatly impacted the regulation of mitochondrial homeostasis. Excessive mechanical stress loading contributes to impairing mitochondrial function, leading to cardiac disorder. Therefore, the concept of restoring mitochondrial function by shutting down the excessive mechanotransduction pathways is a promising therapeutic strategy for cardiovascular diseases. Recently, viral and non-viral protocols have shown potentials in application of gene therapy. This review examines the biological process of mechanotransduction pathways in regulating mitochondrial function in response to mechanical stress during the development of cardiomyopathy and heart failure. We also summarize gene therapy delivery protocols to explore treatments based on mechanical stress–induced mitochondrial dysfunction, to provide new integrative insights into cardiovascular diseases.

Vimentin Association with Nuclear Grooves in Normal MEF 3T3 Cells

Vimentin, an intermediate filament protein present in leukocytes, blood vessel endothelial cells, and multiple mesenchymal cells, such as mouse embryonic fibroblasts (MEF 3T3), is crucial for various cellular processes, as well as for maintaining the integrity and durability (stability) of the cell cytoskeleton. Vimentin intermediate filaments (VIFs) adhere tightly to the nucleus and spread to the lamellipodium and tail of the cell, serving as a connector between the nucleus, and the cell's edges, especially in terms of transferring mechanical signals throughout the cell. How these signals are transmitted exactly remains under investigation. In the presented work, we propose that vimentin is involved in that transition by influencing the shape of the nucleus through the formation of nuclear blebs and grooves, as demonstrated by microscopic observations of healthy MEF (3T3) cells. Grooved, or "coffee beans" nuclei, have, to date, been noticed in several healthy cells; however, these structures are especially frequent in cancer cells-they serve as a significant marker for recognition of multiple cancers. We observed 288 MEF3T3 cells cultured on polyhydroxyoctanoate (PHO), polylactide (PLA), and glass, and we identified grooves, coaligned with vimentin fibers in the nuclei of 47% of cells cultured on PHO, 50% of cells on glass, and 59% of cells growing on PLA. We also observed nuclear blebs and associated their occurrence with the type of substrate used for cell culture. We propose that the higher rate of blebs in the nuclei of cells, cultured on PLA, is related to the microenvironmental features of the substrate, pH in particular.

Carboxypeptidase E, Identified As a Direct Interactor of Growth Hormone, Is Important for Efficient Secretion of the Hormone

We have identified 88 interactor candidates for human growth hormone (GH) by the yeast two-hybrid assay. Among those, we focused our efforts on carboxypeptidase E (CPE), which has been thought to play a key role in sorting prohormones, such as pro-opiomelanocortin (POMC), to regulated secretory vesicles. We found that CPE co-localizes with and interacts with GH in AtT20 pituitary cells. Downregulation of CPE led to decreased levels of GH secretion, consistent with involvement of CPE in GH sorting/secretion. Our binding assay in vitro with bacterially expressed proteins suggested that GH directly interacts with CPE but in a manner different from POMC.

Transferability and inter-laboratory variability assessment of the in vitro bovine oocyte fertilization test

The dramatic increase in the number of animals required for reproductive toxicity testing imposes the validation of alternative methods to reduce the use of laboratory animals. As we previously demonstrated for in vitro maturation test of bovine oocytes, the present study describes the transferability assessment and the inter-laboratory variability of an in vitro test able to identify chemical effects during the process of bovine oocyte fertilization. Eight chemicals with well-known toxic properties (benzo[a]pyrene, busulfan, cadmium chloride, cycloheximide, diethylstilbestrol, ketoconazole, methylacetoacetate, mifepristone/RU-486) were tested in two well-trained laboratories. The statistical analysis demonstrated no differences in the EC50 values for each chemical in within (inter-runs) and in between-laboratory variability of the proposed test. We therefore conclude that the bovine in vitro fertilization test could advance toward the validation process as alternative in vitro method and become part of an integrated testing strategy in order to predict chemical hazards on mammalian fertility.