Embryonic Development Part 2

Hello hello! In this page, let's discuss morphogenesis so we can understand the basics of how embryos develop in the body. This is continuing on from part 1!

One important thing to note in embryonic development is pattern formation - pattern formation is the process by which inductive signals and cytoplasmic determinants create and organize tissues and organs. It's controlled by positional information - basically, the body axes - which is also provied by inductive signals and cytoplasmic determinants.

Homeotic genes specifically control pattern formation all throughout the organism's life - as they're a late embryo, larva, and even adult.

Don't worry if this is confusing - I will explain it. Below is a picture of the body axes.

Now, we must also note that there are mutations with physical outcomes that cause death of the organism as either the embryonic or larval stage. These are embryonoic lethals (shocking name). 

Maternal effect genes, or egg-polarity genes, are specifically genes that, when mutated in the mother, results in mutant physical outcomes in her baby.

In fact, there are genes, that if two are present, offspring can end up having two backsides and no front! These are called bicoid genes.

In a developing fly, you can see that bicoid mRNA is concentrated at the far anterior (front) end of a mature egg. The bicoid protein created from this RNA moves from the front to the back of the offspring, which creates a protein gradient in an early embryo.

These proteins specify the front end of the fly. In all, the material mRNAs left by the mother are extremely important to the embryo and its development. These RNAs help with both the anterior-posterior axis and the dorsal-ventral axis. Later on, miRNAs must destroy these RNAs so they don't end up taking over the organism. Later on, finer aspects must be considered as well, which is done by the positional information encoded by the embryo's genes. This information creates specific amounts of segments and characterizes and orients them. 

However, we must also discuss practical applications of this information - especially in cancer. Cancer causing genes are called oncogenes. 

Proto-oncogenes can become oncogenes by:

• DNA moving in the genome

• becoming amplified

• mutating

Many times, cancer cells have been found to have chromosomes that were broken and rejoined wrong. 

Largely, some important genes that prevent cancer are tumor-suppressor genes. These genes inhibit cell division, so mutations in them can be very serious. Let's discuss a couple of these.

• the ras gene creates the Ras protein, which is a G protein that takes a signal from a growth factor receptor in the plasma membrane to a bunch of protein kinases inside the membrane. Mutations in this can cause issues in the process that usually starts cell division.

• the p53 gene creates a protein that activates a lot of other genes, one of which is p21 (a gene that stops the cell cycle). On top of this, it activates the production of miRNAs and is involved with turning on genes that repair DNA. Along with this, it activates apoptosis genes. In fact, it's called the guardian angel of the genome! You can clearly see how easily this could go wrong, though.

• inherited mutations of cancer itself is often from the APC (adenomatous polyposis coli) gene, which is also a tumor suppressor gene. The protein it creates plays an important role in whether a cell can become a tumor.

In general, the longer we live, the more likely we are to develop cancer - it really is just a matter of time. You know, many cancers are actually caused by viruses - around 15% of them in humans. These are known as tumor viruses and they affect various animals. 

Anyway, now that you know about this, you can ponder over it for the next week while I write my next page on viruses!

As always, thank you so much for reading and have an amazing day! My email is twisha.sharma30@gmail.com if you have any questions! See you in the next one!