From fish to man: Research reveals how fins became legs
Vertebrates' transition to living on land, instead of only in water,
represented a major event in the history of life. Now, researchers
reporting in the December issue of the Cell Press journal Developmental
Cell provide new evidence that the development of hands and feet
occurred through the gain of new DNA elements that activate particular
genes.
"First, and foremost, this finding helps us to understand the power
that the modification of gene expression has on shaping our bodies,"
says Dr. José Luis Gómez-Skarmeta in Spain. "Second, many genetic
diseases are associated with a 'misshaping' of our organs during
development. In the case of genes involved in limb formation, their
abnormal function is associated with diseases such as synpolydactyly and
hand-foot-genital syndrome."
In order to understand how fins may have evolved into limbs,
researchers led by Dr. Gómez-Skarmeta and his colleague Dr. Fernando
Casares at the same institute introduced extra Hoxd13, a gene known to
play a role in distinguishing body parts, at the tip of a zebra-fish
embryo's fin. Surprisingly, this led to the generation of new cartilage
tissue and the reduction of fin tissue - changes that strikingly
recapitulate key aspects of land-animal limb development. The
researchers wondered whether novel Hoxd13 control elements may have
increased Hoxd13 gene expression in the past to cause similar effects
during limb evolution. They turned to a DNA control element that is
known to regulate the activation of Hoxd13 in mouse embryonic limbs and
that is absent in fish.
"We found that in the zebrafish, the mouse Hoxd13 control element was
capable of driving gene expression in the distal fin rudiment. This
result indicates that molecular machinery capable of activating this
control element was also present in the last common ancestor of finned
and legged animals and is proven by its remnants in zebra-fish," says
Dr. Casares.
- ScienceDaily
|