According to EurekAlert!: A study explores the genetic basis for the origin of paired appendages in vertebrate evolution. Jawed vertebrates possess two sets of appendages, such as pectoral and pelvic fins, while extant jawless fish, such as lampreys and hagfish, lack paired fins. However, the fossil record preserves traces of now-extinct jawless fish possessing pectoral fins but lacking pelvic fins.
To explore the origin of paired appendages, Neil Shubin and colleagues compared the expression patterns of the Tbx5 and Tbx4/5 genes in a group of vertebrates involved in the formation of thoracic appendages. The authors found that Tbx4/5 gene expression was confined to the embryonic heart of jawless vertebrates, while in jawed vertebrates, Tbx5 expression extended posteriorly beyond the heart and gill regions. Molecular analysis suggested that a gene expression regulatory element called an enhancer, located near the Tbx5 gene, underpinned the observed expression pattern. When this enhancer—whose sequence was preserved in jawed vertebrates—was modified to drive tbx5 gene expression in a jawed vertebrate, this intervention restored the development of pectoral fin buds in this mutant fish, a zebrafish mutant called heartstrings, which lacks tbx5 expression and pectoral fins.
The authors say that, together with fossil records from the Paleozoic era, these findings suggest that alterations in Tbx5 expression and regulation patterns may be key to the origin of paired appendages in the early history of vertebrate genetics.
New research explores the genetic basis of the origin of paired appendages in vertebrate evolution.
