Amphioxus posee células fluorescentes en su tegumento
Amphioxus, hoy renombrado como Branchiostoma, es un animalillo del Filo Cordata, Subfilo Cefalochordata donde se encuentran los peces cartilaginosos como tiburones, mantarayas y quimeras. El Amphioxus ha sido muy estudiado, ayudando nuestros conocimientos sobre los primeros vertebrados. Dimitri Deheyn y colaboradores del Instituto Scripps de Oceanografía de la Universidad de California en San Diego publican en Biological Bulletin que Amphioxus posee en su epitelio un grupo de células cargadas con proteína verde fluorescente (GFP), algo que se había demostrado en organismos “superiores” como medusas y corales. El trabajo sugiere el posible papel en la protección a irradiaciones solares y como antioxidante de este tipo de proteínas.
Researchers say green fluorescent proteins, which could play role as 'sunscreen' or stress reducer, may be widespread in animal kingdom.
Fluorescent proteins found in nature have been employed in a variety of scientific research purposes, from markers for tracing molecules in biomedicine to probes for testing environmental quality. Until now, such proteins have been identified mostly in jellyfish and corals, leading to the belief that the capacity for fluorescence in animals is exclusive to such primitive creatures.
Scientists at Scripps Institution of Oceanography/UC San Diego have discovered fluorescent-light emitting features in an evolutionarily important marine organism and say such a capacity may be much more prevalent across the animal kingdom than previously believed.
In the cover story of the October issue of Biological Bulletin, Dimitri Deheyn and his colleagues in La Jolla, Calif. and Japan describe finding green fluorescent proteins (GFPs) in Amphioxus, a fish-like animal closely studied by scientists due to its evolutionarily important position at the base of a large phylum of animals called chordates. The researchers say amphioxus' GFPs are very similar to those of corals, an interesting fact since the two animal groups are separated by hundreds of millions of years of evolution.
The finding emphasizes the idea that evolutionary preservation of fluorescence must play an important ecological function, Deheyn said. Many animals haven't been tested for fluorescence and its prevalence in the animal kingdom remains unknown.
Deheyn made the discovery while analyzing a dozen specimens of the small, slender marine animals collected in Tampa, Fla., by Nick Holland, a professor of marine biology at Scripps and a paper coauthor.
“When I put the specimens under the blue light (used for evoking fluorescence), every single amphioxus had a bright green area in the anterior that was fluorescent,” said Deheyn.
Follow-on analyses in the Tampa specimens, along with similar species samples from France and Japan, revealed details of how the fluorescence spreads along the animal's body as well as how the animal fluoresces at different stages of development.
Amphioxus-also called a lancelet-is found primarily in coastal areas and lives mostly burrowed in ocean sand except for its head. Previous studies have shown it to be sensitive to changes in light exposure.
Deheyn says the exact role of amphioxus' fluorescence is not known. One hypothesis is that the proteins might be used as a form of “sunscreen,” protecting the animal by absorbing harmful ultraviolet light and shielding it away as fluorescent light. GFPs also may play a role as protective antioxidants, decreasing stress levels undergone by cells when exposed to temperature fluctuations or other environmental changes.
Fluorescence has been used extensively in biotechnology, biomedicine, bioengineering and lately in nanotechnology. GFPs have been used as markers to examine gene expression as well as probes for tracking how molecules transfer energy.
“(GFP) is an easy protein to work with and to use as a label,” said Deheyn, a scientist in the Marine Biology Research Division at Scripps. “It's easy to locate and stimulate so it has been used widely around the world. There is a great deal of interest in finding new fluorescent compounds and proteins that can show different characteristics of light production.”
Deheyn's latest investigations focus on finding GFPs in animals in marine as well as terrestrial environments.
In addition to Deheyn and Holland, Biological Bulletin paper's coauthors include James McCarthy, Magali Porrachia and Greg Rouse of Scripps Oceanography, Kaoru Kubokawa of the University of Tokyo and Akio Murakami of Kobe University.
The study was funded by the Air Force Office of Scientific Research's Biomimetics, Biomaterials and Biointerfacial Sciences program and the Ministry of Education, Culture, Sports, Science and Technology of Japan.
It's a long way from amphioxus. . .
With about twenty-five species inhabiting shallow tropical and temperate oceans, the Cephalochordata are a very small branch of the animal kingdom. Known as lancelets or as Amphioxus (from the Greek for “both [ends] pointed,” in reference to their shape), cephalochordates are small, eel-like, unprepossessing animals that spend much of their time buried in sand. However, because of their remarkable morphology, they have proved crucial in understanding the morphology and evolution of chordates in general — including vertebrates.The anatomy of a cephalochordate is diagrammed at left. Note that cephalochordates have all the typical chordate features.
The dorsal nerve cord is supported by a muscularized rod, or notochord. The pharynx is perforated by over 100 pharyngeal slits or “gill slits”, which are used to strain food particles out of the water. The musculature of the body is divided up into V-shaped blocks, or myomeres, and there is a post-anal tail. All of these features are shared with vertebrates. On the other hand, cephalochordates lack features found in most or all true vertebrates: the brain is very small and poorly developed, sense organs are also poorly developed, and there are no true vertebrae.
Water is taken in through the mouth, drawn in by the beating of cilia located on the wheel organ, a set of ridges lying inside the mouth. The water is first filtered by the oral cirri, slender projections that surround the opening of the mouth, clearly visible on the photograph at the top of the page. It then passes through the gill slits. These gill slits are enclosed by folds of the body wall, the metapleural folds, to form a body cavity known as the atrium. Food particles in the water are trapped by mucus, while water passes through the slits and out of the atrium through the atriopore, located towards the posterior end. The rest of the digestive system is fairly simple: a pouch or hepatic caecum secretes digestive enzymes, and actual digestion takes place in a specialized part of the intestine known as the iliocolonic ring. Cephalochordates also have a well-developed circulatory system and a simple excretory system composed of paired nephridia. The sexes are separate, and both males and females have multiple paired gonads. Eggs are fertilized externally, and develop into free-swimming, fishlike larvae.
Since cephalochordates have no hard parts, their fossil record is extremely sparse. However, fossil cephalochordates have been found in very old rocks indeed, predating the origin of the vertebrates. The famous Middle Cambrian Burgess Shale of British Columbia has yielded a few fossils of Pikaia, which appears to be a cephalochordate (although the fossils are still being restudied). More recently, Yunnanozoon, from the Early Cambrian of south China, was reported to be a cephalochordate, the earliest known (Chen et al., 1995). These fossils show that the chordate lineage appeared very early in the known history of the animal kingdom, and they strengthen the case for an origin of true vertebrates from a cephalochordate-like ancestor.
Today, amphioxus may be extremely common in shallow sandy environments: at Discovery Bay, Jamaica, up to five thousand individuals per square meter of sand have been reported. In some parts of the world, amphioxus are eaten by humans or by domestic animals; they are important food items in some parts of Asia, where they are commercially harvested.