Hair, Tooth or Scale?
Although at first glance, these three appendages appear to have little in relation to one another, there are intriguing hints of a common developmental origin. Can you guess the identity of today’s Science Mystery Pix?
❋ The Toothless Men of Sind: Our story begins in 1875, with Charles Darwin describing the curious case of a Hindu kindred whose males suffered a near absence of teeth and hair. This inherited condition, known as ectodermal dysplasia, was tracked down to defects in genes coding for a signaling protein (ectodysplasin-A or EDA) and its receptor (EDA receptor or EDAR). Similar hairless and toothless mutations were found in the mutant mouse strains Tabby and Downless, pointing to a common developmental origin for hair and teeth.
❋ Fighting Tooth and Scale : Which came first, teeth or scales? It is thought that the earliest teeth arose in shark-like fish that lived in the Early Devonian period, about 400 million years ago. The pointy tooth-like scales found near the mouth of fossils would have helped grasp prey or fight predators. Eventually, these transformed into the teeth of modern day mammals.
❋ A Fishy Tale: Now for the final link! Mutants of the medaka fish (Oryzias latipes), originally isolated from wild populations, are viable and fertile but completely lack scales. Named rs-3 (for reduced scale-3), the mutation affected the same ectodysplasin-A receptor (EDAR), which is required for the initiation of hair development in mammals. So what do you think..is the image a 20x magnification of hair, tooth or scale?
Image from Dr. Havi Sarfaty of the Israel Veterinary Association and winner of Nikon Small World competition.