Localizing and extracting filament distributions from microscopy images.

Detailed quantitative measurements of biological filament networks represent a crucial step in understanding architecture and structure of cells and tissues, which in turn explain important biological events such as wound healing and cancer metastases. Confocal microscope images of biological specimens marked for different structural proteins constitute an important source for observing and measuring meaningful parameters of biological networks. Unfortunately, current efforts at quantitative estimation of architecture and orientation of biological filament networks from microscopy images are predominantly limited to visual estimation and indirect experimental inference. Here we describe a new method for localizing and extracting filament distributions from 2D confocal microscopy images. The method combines a filter-based detection of pixels likely to contain a filament with a constrained reverse diffusion-based approach for localizing the filaments centrelines. We show with qualitative and quantitative experiments, using both simulated and real data, that the new method can provide more accurate centreline estimates of filament in comparison to other approaches currently available. In addition, we show the algorithm is more robust with respect to variations in the initial filter-based filament detection step often used. We demonstrate the application of the method in extracting quantitative parameters from an experiment that seeks to quantify the effects of carbon nanotubes on actin cytoskeleton in live HeLa cells. We show that their presence can disrupt the overall actin cytoskeletal organization in such cells.

The nucleus as a central structure in defining the mechanical properties of stem cells.

Manipulation of stem cells is one of the highest goals within biological sciences for the development of devices for the regeneration of injured tissues. In general, the mechanical properties of cells are nowadays recognized to play a role in many cellular phenotypes, including mobility though tissues, survival to mechanical loading and differentiation. Here we present a study where the mechanics of bone marrow CD34+ hematopoietic stem cells (CD34+ cells) and bone marrow stromal cells (BMSCs) is investigated through micropipette aspiration. The objective was to address the role of the nucleus as a central mechanoactive structure in stem cells. Stem cell nuclei occupy most of the cell volume and present different properties from what is known for somatic cells. Mechanics revealed to be highly dependent on the nucleus, where CD34+ cells revealed to be stiffer than BMSCs for short times under loading assuming elastic behavior and highly viscoelastic for longer times under loading, which present a higher nuclear volume per cell volume ratio. Mechanics was also evaluated for agglomerates of stem cells by aspirating spheres of neural progenitor cells (NSC-Ss). Relatively to single cells, NSC-Ss presented higher deformability, which seems to be more dependent on intracellular connectivity than on cell mechanics. The general character of the reported conclusions is being investigated with other types of stem cells.