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The origin of the parathyroid gland; persistence of gills in tetrapods
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| Proceeding of the National Academy of Sciences of the United States of America (PNAS) |
| Hiromi laboratory, Division of Developmental Genetics |
The origin of the parathyroid gland.
Okabe M, Graham A.
PNAS, Vol.101 No.51, 17716-17719, 2004
It has been held that the parathyroid glands evolved with the emergence of the tetrapods, reflecting a need for new controls on calcium homeostasis in terrestrial rather than aquatic environments. Developmentally, the parathyroid gland is derived from the pharyngeal pouch endoderm, and, studies in mice, have shown its formation is under the control of a key regulatory gene, Gcm-2. We have used a phylogenetic analysis of Gcm-2 to probe the evolutionary origins of the parathyroid gland. We find that Gcm-2 is not only present in the tetrapods but also in teleosts and chondrichthyans, and is expressed within the endodermal pharyngeal pouches, and the gills that derive from them, in zebrafish (Danio rerio), a teleost, and dogfish (Scyliorhinus canicula), a chondrichthyan. We further demonstrate that Gcm-2 function is required for the formation of the internal gill buds in zebrafish. We have also identified Parathyroid Hormone (PTH) encoding genes in fish, and we show that these genes are expressed by the gills. These results indicate that the tetrapod parathyroid gland likely came into being as a result of the internalisation of the gills during tetrapod evolution.
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Expression of Gcm-2 in a chick embryo (left) and a zebrafish embryo (right). Gcm-2 expressing cells in the pharyngeal pouch endoderm (arrowhead) develop into the parathyroid gland in chick or the gills in zebrafish, respectively, suggesting that these two organs share their evolutional origin.
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