Sea jellyfish is a complex set of genes

A sea jellyfish is angry in the aquarium in California. Inside its seemingly simple body is an extremely complex set of genes.

The life cycle of jellyfish

For years, sea jellyfish have been considered a simple and primitive animal. If we look at the aquarium, we will easily believe this. Similar to those of the same family as anemones and corals, sea jellyfish all seem to be a completely simple animal. It has no tail end, no abdominal back, no right and left, no legs or fins. It also has no heart. Its gut is more like a bag than a pipe, so its mouth will also play an anal role. Instead of the brain, it has only a diffuse neural network.

A fish or a shrimp can move quickly in a certain direction, but the jellyfish can only swim lethargically.

But the most recent research results have led scientists to admit that they underestimated its jellyfish and relatives, known as the cnidarian collection (pronounced nih-DEHR). -ee-uns).Inside their seemingly simple body is a very complex and remarkable set of genes, including many useful for developing human anatomy.

These discoveries led to a completely new theory of the evolution of animals from 600 million years ago. The search results also attracted the attention of many cnidarian scientists as a model for understanding the human body.

Biologist Kevin J. Peterson, a biologist at Dartmouth, said: "The biggest surprise is that cnidarians have more complex genes than we thought. This has caused many people to turn around and realize that many things they still think about cnidarians are completely wrong. "

Scientists have reviewed their development process. 18th-century naturalists were reluctant to put them in the animal world, and that was it. They group cnidarians in the "Tree-shaped Animals" industry, somewhere between animals and plants.

Only in the 19th century did naturalists begin to understand their growth mechanisms from eggs, their bodies growing from two layers of cells, endoderm and epidermis.

Starfish

Other animals, including humans and insects, develop the body in three cell layers: mesoderm, endoderm and epidermis. This mechanism forms muscles, heart and other organs not found in the cnidarian group.

Cnidarians also have a simple mechanism of action. Fish, fruit flies and earthworms completely have tail heads, abdomen, left and right. Scientists refer to the bodies of animals, including humans, by this symmetric mechanism. In contrast, cnidarian species have absolutely no symmetry. For example, sea jellyfish, only symmetrical mechanism in the form of bicycle wheels, from the center out.

Biologists study the evolution of cnidarians as a relic of evolution. The first animals are like sponges, like cells. Cnidarian may represent the next stage of evolution, acquiring the characteristics of simple cell and nervous systems.

Fossil specimens all seem to confirm this hypothesis. Many animal fossils in the early stages have many similarities with jellyfish or other cnidarian species. The oldest fossil specimens that have been found appear in the period called the Cambrian boom, 540 million years ago.

Some researchers argue that double-layer evolution has formed the Cambrian period. Unlike their ancestors, two-layer animals have heads, allowing them to be aware of their surroundings and control their movement.

Latest research has changed this theory. The oldest fossils classified as cnidarians are only about 540 million years old. Dr. Peterson and his colleagues propose a mechanism for evaluating the age of cnidarians by studying their DNA.

Structure and life cycle of Obelia - Cnidarians

DNA changes at a normal pace from millions of years, according to the molecular clock mechanism. Dr. Peterson judged that the ancestors of the cnidarians lived in the period of about 543 million years ago. In other words, cnidarian cannot appear before two-layer animals ten million years.

Genetic studies have also challenged all traditional theories about cnidarians. Beginning in the 1980s, scientists studying two-layer animals found a system of genes that formed their bodies. Some genes form the tail-tip axis, others form the back axis.

Humans and insects can be very different, but they all follow the most basic developmental points of this genetic law. The results show that this genetic law has evolved from the ancestral species of two-layer animals.

Dr. Mark E. Martindale of the University of Hawaii and his colleagues decided to look for a gene system that forms the jellyfish body and other species in the cnidarian group. They take a lot of time to get results. They have to find species that not only live in the laboratory but also have the ability to produce a fetus for the research process.

Dr. Martindale's group selected star-shaped anemones, a species of animals abundant on the coast of New England. Understanding the life cycle and studying the genetic mechanism of this species is a requirement that requires a lot of patience. Dr. Martindale said, "It took us 9 to 10 years, but its results are like a gold mine."

The researchers were surprised to learn that some of the genes in their embryos have a structure similar to those of genes that regulate the tail end of a two-layer animal, including humans. Even more surprising when they realized that these genes acted in a completely identical mechanism as the tail-end mechanism of two-species species.

Subsequent research results show that cnidarians also have a number of other genes that also follow symmetric genetics. The genes that support the abdominal back axis formation are also formed on the opposite side of the embryo of anemones.

The search results have led scientists to question why cnidarians use such a complex set of body-building genes while their bodies seem so simple. They came to the conclusion that the cnidarians may be complex in their appearance, especially in the nervous system.

"At the molecular level, their bodies have many unrecognizable areas," said John R. Finnerty, a Boston biologist working with Dr. Martindale .

Dr. Finnerty believes that the cnidarians' nervous system will be a completely complex system."The cnidarians' neural organ is structured like a neural network, but it's a simplified description of the textbook," he said.

Anemone - Cnidarians

He also predicts that research results will show that this neural network is divided into separate areas dedicated to the human brain.

These discoveries make Dr. Peterson reconsider the evolution of cnidarians."It has completely changed my mind about the evolution of animals in the first period," he said.

Now that he thinks cnidarian is not simply one of the first formations in the Cambrian boom period, but one of the species in this period, its evolution is controlled by law. of carnivores.

In an article published in Paleobiology, Dr. Peterson and his colleagues proposed the common ancestor theory of both bivalve species and the cnidarian group as an insect. This ancient insect, according to Dr. Peterson, lived in a period of about 600 million years ago, representing an important evolutionary pattern in animal evolution. Instead of simply filtering small prey, it has the ability to catch larger prey.

Dr. Peterson said: "When they can find their own bait, nothing can stop them."

Some of these species began to eat each other. Any animal with higher defenses will be able to survive. One way to not be eaten is to make your body grow bigger. Another way is to lay eggs in the water column instead of being bare on the sea floor. Some animals also have the ability to swim as adults.

When the water environment begins to have many animals, the cnidarians transform their bodies as they are today. Early cnidarians animals anchored themselves to the bottom of the sea and developed upward, similar to anemones and corals as they are today. In the process of development, they destroy the mechanism of symmetry of their ancestors.

At the same time, the cnidarian formed his special weapon: the cells formed small spikes called nematocytes, the poison that paralyzed the prey.

Starfish

Dr. Peterson thinks that when modern animals move higher in water columns, some cnidarians evolve to be able to hunt down prey. Sea jellyfish is the final product of this evolutionary process.

New discoveries about cnidarians have led to the need for people to study them more closely. Star anemones are being studied at Genome Energy Department's Joint Genome Institute, which is expected to complete the research this year.

Scientists are waiting for many surprises from this genetic study. They have found many types of genes similar to vertebrates in the cnidarian gene system. Clearly these genes cannot be formed in early vertebrate species.

They are older, related to the ancestors of cnidarians and bivalve animals from 600 million years ago. Later, they disappeared in the development branch of two-layer animals such as insects and nematodes, which are now very popular in research projects.

At some point, the cnidarian group is a research model that is more useful for human body biology than fruit flies. It may be a very amazing thing, but when looking at a jellyfish in a fish tank, it's like we're looking at the mirror.