A comparative study of microtubules in some vertebrate and invertebrate cells

Summary An electron microscope study of a variety of invertebrate and vertebrate cell types has supported the postulate that the microtubule is a universal cellular organelle. Microtubules of similar dimensions have been observed in the flagellum and beneath the plasma membrane of Trypanosoma lewisi, in the flagellum, manchette and mitotic spindle of the earthworm (Lumbricus terrestris) spermatid; and in fibroblasts, proximal convoluted and collecting tubule cells of the hypertrophying rat kidney. The specific occurrence and organization of the microtubules in cells undergoing morphological and developmental changes have suggested that these organelles are contractile and that they effectively contribute to the maintenance of cellular form. The possibility that microtubules may function as an intracellular transport system is also suggested.This work was supported by grants CA-04046, GM-08380, and K 3-AM-4932 from the U. S. Public Health Service.     

A system to reproduce and quantify the biomechanical environment of the cell

An in vitro system that permits application of a uniform biomechanical stimulus to a population of cells with great precision has been developed. The device is designed to subject living cells to reproducible and quantifiable biaxial strains from 0 to 10% at rates from quasi-static to 1 s-1 and frequencies from 0 to 5 Hz. Equations for determining the strain in the substrate upon which the cells are grown, based on easily measured parameters, are derived and validated experimentally. The mechanical properties of the substrate are determined, and it is demonstrated that cells can easily be cultured in the apparatus. By use of the system, cloned bovine pulmonary artery endothelial cell clones are subjected to 5% biaxial strains applied at a peak strain rate of 0.5 s-1 and a frequency of 1 Hz for 7 h with cell viability greater than 84% and cell detachment less than 8%. We demonstrate that cells must be attached to the substrate for them to be stretched and that cell strain and substrate strain are not equal. With the use of fluorescently labeled beads as cell surface markers to measure the actual strain produced in the cells as a result of the deformation of the substrate, cell elongation was found to be approximately 60% of the strain in the substrate. This constant appeared to be affected by both in vitro cell age and morphology.     

A simple program which processes liquid scintillation counting data from samples containing both 125I and 3H under conditions of varying quench

A simple program was written for a programmable calculator which enabled simultaneous measurement of ³H and ¹²⁵I by liquid scintillation counting. The program uses quench correction curves to calculate the effects of quench in each sample and calculates the amount of each isotope present by solving a linear equation set simultaneously.     

Cell density regulates prolyl 4-hydroxylase activity independent of mRNA levels

In embryonic avian tendon, cell density regulates collagen production. This control is propagated through the alpha-subunit of prolyl 4-hydroxylase where protein levels were previously shown to rise fivefold with increasing cell density. In contrast, mRNA levels are now shown not to change by both Northern and RNAse protection assays. This lack of increase contrasts with previous reports as does the mRNA length: this is 50% larger as confirmed by sequencing the 3' end. Alternative sites for cell density regulation of the enzyme could rely on its sensitivity to sulfhydryl groups. Using a fluorescent sulfhydryl probe as well as a sulfhydryl inhibitor, one observes a strong cell density response, supporting the hypothesis that cellular redox potential could alter protein stability.