Another cell population thought to be static throughout life turns out to be capable of regeneration and renewal, given the right cues: "Damage to podocytes - a specialized type of epithelial cell in the kidney - occurs in more than 90 percent of all chronic kidney disease. Now researchers [have] uncovered an unexpected pathway that reveals for the first time how these cells may regenerate and renew themselves during normal kidney function. ... Podocytes are found only in the kidney and are an integral structural component of its blood-filtering system. They stand shoulder-to-shoulder in a part of the organ called the glomerulus and wrap their long 'feet' around the semi-permeable capillaries through which blood flows. Narrow slits between the feet allow small molecules, such as water and salts, to pass while blocking large proteins. This filtering process is the first step to forming urine, and it is critically important - even one missing cell can leave a gap that would allow unwanted molecules through the barrier. ... It used to be thought that you were born with podocytes, and you died with the same podocytes - you don't make any more during your lifetime. ... The problem was, such a scenario doesn't make a lot of evolutionary sense - particularly when other epithelial cells routinely regenerate themselves. ... Podocytes may utilize recognized pathways of regeneration to renew themselves throughout life, [and] people suffering from chronic kidney disease may simply have worn out or outpaced their podocytes' capacity for renewal ... Now that the researchers know podocytes have the ability to regenerate in response to common cellular signals, their next step is to learn whether this regeneration occurs in healthy animals and people. ... If we can harness this regeneration, we may one day be able to treat people with chronic kidney disease."