Stem cell-derived retinal cells
Stem cell-derived retinal cells. Fluorescence light micrograph of retinal pigment epithelium (RPE) cells that have been derived from human embryonic stem cells (HESC). ZO-1 tight junction protein is green, and cell nuclei are red. RPE is the pigmented cell layer just outside the retina in the eye that nourishes retinal visual cells. HESC are pluripotent - they are able to differentiate into any of the 200 cell types in the human body. The type of cell they mature into depends upon the biochemical signals received by the immature cells. This ability makes them a potential source of cells to repair damaged tissue in diseases such as Parkinson's and insulin-dependent diabetes.
© SILVIA RICCARDI/SCIENCE PHOTO LIBRARY
Ovarian primordial follicles, micrograph
Ovarian primordial follicles. Light micrograph of a section through the cortex of a neonatal ovary, showing clusters of primordial follicles each containing a single oocyte (egg cell) surrounded by a layer of follicle, or granulose, cells. The oocytes are the female germline cells. At birth in humans there may be up to one million primordial follicles in a pair of ovaries. Primordial follicles remain arrested in development until activated to enter a prolonged growth and maturation phase called folliculogenesis. In postnatal and early adult life perhaps 10-20 primordial follicles are recruited each day to enter the follicular growth process resulting in the gradual decline in their number such that at menopause, only a few hundred remain. Magnification:
© MICROSCAPE/SCIENCE PHOTO LIBRARY
Stem cell, SEM
Stem cell, coloured scanning electron micrograph (SEM). Stem cells can differentiate into any other cell type. There are three main types of mammalian stem cell: embryonic stem cells, derived from blastocysts; adult stem cells, which are found in some adult tissues; and cord blood stem cells, which are found in the umbilical cord. The cell seen here is destined to become a blood cell. During blood cell development in adults, stem cells develop through a process known as haemopoiesis. Blood cells have short lifespans and are therefore constantly produced by the bone marrow.
© SCIENCE PHOTO LIBRARY