March 2, 2014
Elephant Shark Summary
During the Paleozoic era, about 450 million years ago, a separation occurred in gnathostomes. Gnathostome creatures are vertebrates that have paired fins and a hinged jaw, but separated by weather they are a bony vertebrate, or a cartilaginous. Bony fish are formally known as osteichthyes, they include fish with ossified endoskeletons such as a salmon would have. Cartilaginous fishes on the contrary have cartilage endoskeletons, and are referred to as chondrichthyes. These fish evolved from each other over time, and by analyzing their genomes we can obtain insights on their ancestry. What can make this possible is the elephant shark (Callorhinchus milii). Exclusive from other chondrichthyes, elephant sharks genomes are relatively small and have evolved the slowest of any other vertebrate known today. With this information at our disposal we can gain a greater comprehension for the beginning of adaptive immunity, and what caused gnathostomes to separate millions of years ago.
When comparing the immune systems of cartilaginous fish to mammals you see numerous similarities, but the traits that make them different are distinct. The genome assembly appears to be related to the immuno-globulin and T-cell receptor genes, and also retains unusually low subsets of T helper cells with unconventional antigen-binding properties. Antigen receptor genes matched up with specific MHC genes displays co-evolution of antigen presentation and recondition. Early osteichthyes show a similar MHC gene, only more sophisticated. Elephant sharks immune-genome show resilience while in contact with cytotoxic natural-killer and CD8+ T cells. This immunity proposes a primitive function to give chondrichthyes an added advantage.
The genome of the elephant shark can expose and answer why the endoskeletons of chondrichthyes are not ossified bones. All genes family members necessary to form bones are present, besides the...