STEM CELL DIFFERENTIATION IN SPONGES

One big question in science is how animals, including us, came to be in the course of evolution. All animals consist of large numbers of cells, distributed in different types, each type with a specific role within the organism, and all working together to keep the organism functioning correctly. One common feature of all animals, is the presence of a special type of cells, called stem cells, which are able to replicate themselves and to replace other types of cells when these die. The process by which stem cells convert themselves into other cell types is called differentiation. Stem cell differentiation is very important to maintain the body of the animal in its healthy state, with the correct number of cells of each type, and it plays a critical role during regeneration of body parts that have been damaged. It is thought that the first animal, from which all of us came, evolved from a unicellular organism about 700 million years ago, but how this happened remains a mystery. This project will try to shed some light onto this interesting question. One hypothesis is that before the first animal had evolved, some unicellular organisms existed that were able to replicate themselves and to change between different cell forms. It is possible, then, that the first animal evolved from such a unicellular organism, by sticking together many cells of this unicellular organism, and using the mechanisms to change cell form for stem cell differentiation. Our goal is to put this hypothesis to the test. But how can one explore what happened 700 milion years ago without a time machine? Scientists have discovered that some animals, like sponges, evolved very early after the first animal appeared. Sponges are very simple animals: although they do have stem cells that can help regenerate body parts, they do not have any neurons, muscles or organs, like eyes, ears or a heart. By studing how stem cells of these simple animals differentiate into other cells types, we can find clues about how the stem cells of the first animals differentiated. In addition, we are looking at how some very interesting unicellular organisms can change cell form. What is interesting about these unicellular organisms is that they are thought to be the grand, grand, grand (and many times grand) children of the unicellular organism that existed 700 million years ago and gave rise to the first animal. By comparing the mechanisms used by sponge stem cells to differentiate, with the mechanisms used by the unicellulars to change cell form, we hope to be able to tell whether these mechanisms are related, and therefore, to be able learn about how animals evolved.