Design and analysis of a long-term live-cell imaging chamber for tracking cellular dynamics within cultured human islets of Langerhans

Constrained watershed method to infer morphology of mammalian cells in microscopic images

Precise information about the size, shape, temporal dynamics, and spatial distribution of cells is beneficial for the understanding of cell behavior and may play a key role in drug development, regenerative medicine, and disease research. The traditional method of manual observation and measurement of cells from microscopic images is tedious, expensive, and time consuming. Thus, automated methods are in high demand, especially given the increasing quantity of cell data being collected. In this article, an automated method to measure cell morphology from microscopic images is proposed to outline the boundaries of individual hematopoietic stem cells (HSCs). The proposed method outlines the cell regions using a constrained watershed method which is derived as an inverse problem. The experimental results generated by applying the proposed method to different HSC image sequences showed robust performance to detect and segment individual and dividing cells. The performance of the proposed method for individual cell segmentation for single frame high-resolution images was more than 97%, and decreased slightly to 90% for low-resolution multiframe stitched images.

A microfluidic positioning chamber for long-term live-cell imaging

We report a microfluidic positioning chamber (MPC) that can rapidly and repeatedly relocate the same imaging area on a microscope stage. The "roof" of the microfluidic chamber was printed with serials of coordinate numbers that act as positioning marks for mammalian cells that grow attached to the "floor" of the microfluidic chamber. MPC cell culture chamber provided a simple solution for tracking the same cell or groups of cells over days or weeks. The positioning marks were used to register time-lapse images of the same imaging area to single-pixel accuracy. Using MPC cell culture chamber, we tracked the migration, division, and differentiation of individual PC12 cells for over a week using bright field and fluorescence imaging.

Human ESC colony formation is dependent on interplay between self-renewing hESCs and unique precursors responsible for niche generation

Human embryonic stem cell (hESC) cultures are heterogeneous and constituting paracrine signals are required to maintain pluripotency. The cellular interplay and dynamic nature of this heterogeneity is not understood. Here, long-term hESC imaging and tracking revealed that hESC heterogeneity is dynamic and hESC self-renewal is dependent on colony-proximal distributions of paracrine signals. Tracking of hESCs forming colonies revealed that a biologically distinct cell type arises at the colony periphery in the absence of feeders. Higher rates of cell death occur in these hESC-derived cells, leading to clonal selection of colony reestablishing cells. hESC-derived feeders co-transferred during passaging promoted rapid colony recovery and expansion and reduced overall clonal selection of self-renewing hESCs. Our findings demonstrate that hESC-derived feeders arise from a distinct subpopulation of hESCs that respond to paracrine cues at the colony periphery that are required to sustain and establish clonal hESC self-renewal.

In vivo imaging of murine endocrine islets of Langerhans with extended-focus optical coherence microscopy

AIMS/HYPOTHESIS

Structural and functional imaging of the islets of Langerhans and the insulin-secreting beta cells represents a significant challenge and a long-lasting objective in diabetes research. In vivo microscopy offers a valuable insight into beta cell function but has severe limitations regarding sample labelling, imaging speed and depth, and was primarily performed on isolated islets lacking native innervations and vascularisation. This article introduces extended-focus optical coherence microscopy (xfOCM) to image murine pancreatic islets in their natural environment in situ, i.e. in vivo and in a label-free condition.

METHODS

Ex vivo measurements on excised pancreases were performed and validated by standard immunohistochemistry to investigate the structures that can be observed with xfOCM. The influence of streptozotocin on the signature of the islets was investigated in a second step. Finally, xfOCM was applied to make measurements of the murine pancreas in situ and in vivo.

RESULTS

xfOCM circumvents the fundamental physical limit that trades lateral resolution for depth of field, and achieves fast volumetric imaging with high resolution in all three dimensions. It allows label-free visualisation of pancreatic lobules, ducts, blood vessels and individual islets of Langerhans ex vivo and in vivo, and detects streptozotocin-induced islet destruction.

CONCLUSIONS/INTERPRETATION

Our results demonstrate the potential value of xfOCM in high-resolution in vivo studies to assess islet structure and function in animal models of diabetes, aiming towards its use in longitudinal studies of diabetes progression and islet transplants.