Eli5: How do bones and other organs know what shapes to grown into?
In: 3675
Rootcell: *chillin*
DNA: Yo wassup man
Rootcell: Wassup homie
DNA: So I got yo growin’ plan, you gon grow into an intestine tissue cell a’ight?
Rootcell: Bet
DNA: Good luck my g
Rootcell: Thanks bro
This topic may be too complicated for ELI5. There are a lot of genes that produce growth factors, and many of these genes are expressed only at specific times and in specific places. The location and timing are controlled by other genes making other transcription factors or inhibitors or whatever, also at very specific times and places.
Sometimes growth depends not just on a growth factor being produced somewhere, but on that factor diffusing outward through nearby tissues, producing a concentration gradient. The gradient gives a sense of direction to the tissue growth.
Sometimes the shapes of growing organs are affected by the shapes of everything growing around them. Sometimes the growth of one tissue layer is faster than another, which causes them both to fold or bulge or take other shapes. Sometimes even the stretching and straining of tissues being pulled around by other growing parts triggers these tissues to make their own growth factors.
This is tangential to your question, but sometimes the shape doesn’t even come from growing, it comes from dying. Fingers work that way – your hand starts developing almost as a flipper, and the cells in between where your fingers should be undergo programmed cell death.
It’s time for [a song!](https://www.youtube.com/watch?v=ydqReeTV_vk).
Basically DNA has switches that turn on or off production of specific components, based on chemicals that present around the cell.
Basically you start off as a butthole but all of your cells are pre-programmed (they are called stem cells) to know what kind of cell to turn into. It might be a bone cell, might be a hair cell, might be an organ cell
Imagine a crowd of identical people, only differing by age. Now the oldest one, who is in the middle, sprays a perfume. Each person in the crowd follows the same rules: if they smell a lot of perfume, they turn into a heart cell. If they smell a medium amount, they turn into a kidney cell. If they only smell a little, they turn into a liver cell. The person that sprayed the perfume created what is called a “chemical gradient”, which allows the other people to know where in the body they are located. This is one way cells know how to turn into different things and shapes (they “differentiate”).
Here is the super ELI5. Imagine you have a puzzle. You remove a bunch of pieces then fold it up. That’s dna. It basically unfolds and combines with the bits floating around until it’s the shape of the puzzle you started with.
This question is still being actively answered in the field of Developmental Biology. One way it is studied is by turning on and off different genes or sets of genetic information in order to see the effect it has on the organism as it grows up
Before an embryo develops specialized cells (bone cells, vascular etc.) it’s cells are able to change into different types. Think of it like a person’s musical taste, before it is defined it can be influenced, and it can be on a spectrum.
Pretend our embryo is earth in 1965. The Beatles just released Revolver. As the groovyness of the Beatles radiates from the UK people closer to the UK will be more likely to have a bowl cut.
At the same time The Beach Boys come out with Help Me Rhonda. As the funky tunes of spread from California, people closer will be more likely to become surf bums.
On different places on the globe people will have different combinations of these tastes.
UK 100% bowl cut——‐————————-vascular tissue
California 100% surf bum———‐———-bone tissue
Santiago 30% bowl cut 60% surf bum- cartilage tissue
Etc.
Each person will have a different ratio of these two musical taste. These ratios allow people to be unique in their tastes (like different cell types).
Now add Bob Dylan releasing Rolling Stone from Minnesota and we have added another layer influencing the diversity of musical taste…. leading to more “types”.
Imagine you are making a map. As the map grows you need to figure out borders between countries. So you make a system to say where and when things have to change. Cells in the embryo, specifically stem cell, start to trade information with other cells to tell each other where on the map they think they are. The dna in the cells combined with the signals they receive from neighbors combined with markers blocking or allowing access to the dna tell cells what type of cell they need to develop into. It’s basically a very well orchestrated game of telephone.
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