Last week, we explored a simple picture of what is necessary to build a cell. We saw that only a few varieties of raw materials are needed by the cell (including nutrients, amino acids, energy, salt water and oxygen). The DNA plans found in the nucleus and a properly organized work force with messengers then go about building the cell and staffing it. Although there is incredible complexity in how all of the pieces of a cell are assembled, once a living cell is assembled, it is not difficult to duplicate. In fact living cells will automatically duplicate themselves by copying their DNA and dividing, building two similar cells from the materials found in one of them and they won’t stop dividing until they encounter cell neighbors that tell them to stop or they run out of raw materials. It might be surprising to some people that the cells inside us can live outside of our body. Scientists can take most any type of cells out of our body and grow them in a glass dish. As long as they are supplied with sufficient raw materials and messenger molecules, they will continue to grow in the dish. There are many samples of living cells from people who have died more than 50 years ago. It makes you wonder, if we were smart enough to feed our own cells the raw materials and nutrients they need, our cells would be much stronger and last much longer.
The most interesting question to ask now is, what exactly determines the kind of cell (skin cell, muscle cell, brain cell, etc.) that is being built? The answer is not found solely in the DNA. Keep in mind that every single cell inside us has the complete DNA instructions to build any other kind of cell in our body. The marvelous mystery of how we are all put together with all of the thousands of different types of cells in our body is found in the signaling molecules and messengers surrounding our cells that are being passed around between and inside our cells. What does this mean? It means that every cell in our body is built the way it is and works as it should because of the messengers in the environment where it lives. If a cell lives in the heart, it works like a heart cell because of the messengers passed around from neighboring heart cells. If a cell lives in the brain, it works like a brain cell, again, because of the messengers passed around in the neighborhood where it lives. Can I ask the crazy question, does that mean if I took a brain cell out of the brain neighborhood and placed it into the heart neighborhood, would it somehow listen to the surrounding messengers and transform into a working heart cell? It sounds a bit like science fiction. The answer is surprising and alluring.
There are cells in your body, called “stem cells” (produced in different areas of the body, like the stomach fat) that do transform into any type of cells they attach to. So if a stem cell attaches in the heart, it will build itself into a heart cell. If it attaches to the brain, it will build itself into a brain cell. Once stem cells have transformed, however, they are “locked in”. Say stem cells attached to the heart and have transformed into heart cells, these cells themselves start to produce the messengers found in the heart cells in their neighborhood. This sort of “locks them in” to being heart cells in the neighborhood they are in by the “heart cell” messengers they themselves start producing.
The incredible ability of stem cells to transform has been proven thousands of times over. Scientists have taken stem cells out of the body and grown them in dishes. They then have divided the same identical stem cells into three separate dishes. In the first dish, along with the nutrient broth, they placed the molecular messengers found in kidney cells, in the second dish those in liver cells, and the third those in heart cells. The cells in the first dish became kidney cells, the second dish liver cells, and the third, of course, heart cells. And we have not even started to enter the “rabbit hole” yet. This gets deeper and more interesting and stranger the deeper we go. We have found that just by placing stem cells together in communication with other cells they start to assemble and build themselves into complete tissues, with blood vessels, tubes and layers, and all other types of cells needed in the neighborhoods to recreate the living tissue. On the internet you can see videos where whole working kidneys are “printed out” by 3-D printers that just spray out layers of certain types of cells found in kidneys. In hours these cells start to self-assemble into the incredible complexity of a working kidney that can even start to filter blood and produce urine. From the messengers they are passing back and forth, cells can transform into exactly the types of cells needed in the place where they are to produce all of the living tissues needed in the neighborhood where they live. Single cells have the ability to assemble whole neighborhoods of cells and tissues. Scientists have even cloned a whole animal (remember Dolly the sheep) by placing DNA from a skin cell inside an Egg cell. The transplanted DNA started reacting to the messengers inside the egg cell. The cell transformed into a viable Egg cell and started dividing to produce the developing fetus of a whole animal. The ability of a single cell is absolutely incredible. This ability comes from the ability of the internal workings and DNA of the cell to read and respond to environmental messengers. I suppose you can say that a cell is what it eats, literally.
Right now, scientists are creating working organs in laboratories that may even have the potential to rebuild or replace deficient organs with new organs or tissues built in the laboratory, or in our bodies using stem cells. The picture on the top of this post is of a living functioning rat heart self-assembled by rat stem cells placed on a heart frame. After a few days, the heart self-assembled from a bunch of stem cells and even started beating. The possibilities are endless.
A side note: as we study the fascinating dynamics of our cell communities as they build themselves, we also have learned that besides the messengers being passed around that determine what our cells become, our cells are also programmed to respond to what we eat. What we eat literally changes the type of cells we have and how they work. Our body are made to break down the nutrients found in raw plants and meats in our environment and convert them into the molecules our cells need to thrive. Anything more or less than this can severely stress our cells and systems. More than anything else, what we eat makes a difference. Did you know that even our DNA changes with our environment? We have molecular machines inside our cells that integrate genetic material found in our environment and graft them into our own DNA. It should not be so surprising, this is how viruses work. Viruses contain genetic material that are integrated into the DNA of infected cells that codes to produce more viruses of the same sort. Snippets of DNA are readily shared between cells and may comprise some of the messengers that we have been considering that change the function of our cells based on the environment in the neighborhood where they exist. All of this knowledge can work together for our benefit. Think of the possibilities, heed the warnings we feel in our hearts. Life is truly beautiful.