Cell Fate Specification: Cytoplasmic Determinants & Inductive Signals

Cell Fate Specification: Cytoplasmic Determinants & Inductive Signals
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  • 00:00 Cell Fate Specification
  • 1:30 Autonomous Specification
  • 3:16 Conditional Specification
  • 4:58 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

As embryos develop, the new cells need to figure out what their role is in the organism. In this lesson we'll look at the stage called cell fate specification and explore how this is impacted by determinants and inductive signals.

Cell Fate Specification

Are our futures a matter of fate or are they determined by our choices? Don't look at me, I've got no idea. This philosophical question haunts many people. But in biology, it's actually a little simpler. You see, during sexual reproduction, newly fertilized cells contain all of the genetic information needed for that individual. As they start dividing into the hundreds of thousands of cells needed to create functional offspring, each new cell contains all of that same genetic information.

So, technically, it can become any kind of cell, making it totipotent. But at some point, this changes. The potency of the cell decreases, meaning it loses the ability to become anything and eventually becomes determined, or establishes an irreversible fate if left alone. This cell is fated to become a skin cell, this one a blood cell. It's not a matter of choice, it's a matter of which genes are activated.

But this doesn't just suddenly happen. Guiding the transition between cells that can become anything and cells with their own particular fates is a complex process involving cell fate specification, the state of development in which a cell has acquired a fate but it can still be changed. So how does this work? Maybe it's the cell's choice? Or maybe, it's just fate.

Autonomous Specification

Cell specification can happen in one of two main ways. The first is autonomous specification, the development of reversible cell fate without external influence. New cells are created by cleavage division of the zygote, called blastomeres, and during autonomous specification they start to become distinct types of cells based on the composition of the zygotic cell. The unfertilized egg contains various organelles and a liquid solution that fills the cell, called the cytoplasm. Within that cytoplasm are various molecules containing genetic information or chemicals to spark various reactions, called cytoplasmic determinants. Some are different kinds of proteins, most are molecules of RNA. These determinants are unevenly distributed across the egg and then, once it's fertilized, the zygote. Once this zygote undergoes cleavage division, all of these random determinants that were in the same cell are suddenly in different blastomere cells. Which means that these blastomeres each contain a different assortment of molecules.

Okay, so if we call these things determinants, any guess what they do? Yeah. They determine things. Specifically, cell fate. When genetic material in each blastomere is exposed to various determinants. It starts the process of activating and silencing specific gene sequences and that cell becomes specified. Now remember, at this point the cell's fate has been established but can still change. Specification is just the first step in figuring out what the cell will be. It can still change its fate through various mechanisms.

Conditional Specification

One of those mechanisms is also the other kind of cell fate specification. Conditional specification is basically just the opposite of autonomous specification. While autonomous specification relies on molecules within the cell, conditional specification is the development of reversible cell fate based on external influences. What are those influences? Basically, other developing cells.

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