Many of the tissues in our body are constantly renewing, but none so fast as the lining of our gut. Each epithelial cell lining the human intestine lasts about a week. They start life in deep pits called crypts and, as they age, are pushed further up the steep sides of tiny projections called villi, which protrude into the intestinal space. At the tips of the villi, the cells die and detach. Scientists can now examine the lives of gut cells in more detail thanks to a clever labeling trick whereby stem cells in the crypts randomly switch on one of four fluorescent proteins (red, yellow, green or blue). Pictured is a crypt showing epithelial descendants each bearing the colour of its stem cell, making it easy to trace the origins of these short-lived cells.
Three-dimensional image of mitochondria (cyan blue) and cell nuclei (red) in the early embryo of the nematode worm Caenorhabditis elegans, obtained using the super-resolution OMX microscope. Mitochondria function as cellular power plants and produce the energy needed for most cellular functions.
photographie de Ehsan Pourkarimi (Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences)
High Voltage transmission electron micrograph of human female (HeLa) mitotic chromosomes from metaphase arrested cell swollen in hypotonic medium and recorded at 1 MeV. This image was taken with a specimen tilt of 45 degrees. Grouped with it is an image of the same area at 55 degrees tilt, providing an oblique stereo view of the chromosome.
source : Cell Image Library
Dictyostelium discoideum or slime mold, is an amoeba; a single-celled organism, which spends most of its life on a diet of soil bacteria. Faced with famine, it has the unusual ability to form a ‘social’ structure to escape starvation. Amoebas clump together to form a ‘slug’ (bottom, left) that moves towards light. When the slug stops the cell-collective forms a fruiting body (far right), in which some cells die causing their companions to distribute widely (sporulation), in search of a better place to live. Dictyostelium is also a useful model organism. Many aspects of cellular biology in scenarios of health, disease and development depend on the ability of individual cells to communicate with their neighbours like these amoebas do. Many slime mold genes have human counterparts, so this amoeba can be used to investigate genes and test drugs of potential benefit to human health.
source : BoD 03/04/12
Biological Sciences Electron Microscopy Laboratory, Texas Tech University.