Embryonic Development Part 1

Embryonic development - a fascinating topic. Have you ever wondered how one single cell becomes so many specialized cells that eventually become an entire functioning organism? How does a cell know what it needs to specialize in? How do the cells even know where to go? 

The process that governs this is not entirely known yet, but what we do know is so amazing that I had to share it. It's very complicated, so if you haven't been reading my previous pages, you may not understand.

Embryonic development results from three main things:

• cell division

• cell differentiation (specialization of cells in structure and function and organization into tissues and organs)

• morphogenesis (physical processes that give an organism its shape)

We already know about cell division - it is simply the process where cells replicate divide into more cells. So, in this page, I will discuss cell differentiation. In part 2, I will discuss morphogenesis.

With that, let's begin. The key is that each cell type has different activators. But how exactly does that work?

Each egg has certain materials in it, set up by the mother, that create a program of gene regulation that is carried out as cells divide.

Two sources of information that tell a cell which genes to express during development are:

1. The cytoplasm: The cytoplasm contains both RNA and proteins encoded by the mother's DNA. It is filled with mRNA, proteins, organelles, and other substances that are distributed unevenly. Early mitotic divisions distribute the cytoplasm into separate cells.

2. The environment around a particular cell: Signals on an embryonic cell from other embryonic cells in the vicinity (including contact with cell-surface molecules and binding of growth factors secreted by neigboring cells) cause induction in the target cells, driving them along one developmental path.

Cytoplasmic determinants are material substances in the egg that influence the course of early development. Since the cytoplasm has unevenly split materials, as the cell rapidly divides, different activators and proteins are put in different cells, leading those cells along different developmental pathways. Then, diffrentiated cells are specialized to make tissue-specific proteins. In the cast of muscle cells, or myoblasts, the molecular basis of determination is the expression of one or more master regulatory genes.

For example, myoD encodes the MyoD protein, which helps stimulate expression for many target genes. MyoD also stimulates myoD itself. Then, the secondary transcription factors activate the genes for proteins like moysin and actin that confer the unique properties of skeletal muscle cells. myoD is capable of changing some fully diffrentiated nonmuscle cells like fat and liver cells into muscle cells. However, it does not work on everything, as other cells need a particular combination of regulatory proteins, some of which are lacking in cells that do not respond to MyoD. 

This was a short page, but it has important content you should consider before I move on to morphogenesis. Well, that is it for this page! I hope to see you in the next one. My email is twisha.sharma30@gmail.com if you have any questions.