1. Cellular Differentiation
From Embryo to Organism
References:

2. Undifferentiated cells

4. Same Genetic Material, yet Different Cells
Differentiation: a process in which a cell acquires a certain type.
Undifferentiated: has not yet established a type.

5. The zygote starts with 50% of the genetic material from the father and 50% from the mother.
All cells have the same genetic material.
Yet, these cells will have different fates.
How do they know what to become?
Certain genes become activated, other genes become inactivated.
This process happens often during differentiation in a timely manner.

7. Some Definitions
Pluripotent: cells can differentiate into many different cells.
Totipotent is the original zygote. It gives rise to ALL the cells of the organism
Multipotent can differentiate only into certain types of cells, but still can reproduce.
Unipotent is a cell, with ability to develop only into one type of cell.

9. So what are stem cells?
Stem cells are cells that continue to divide, and remain undifferentiated. 
In plants specialized cells can de-differentiate (vegetative reproduction)
In each stem cell division, one cell remains a stem cell, while the other goes on to differentiate. 
The differentiating daughter, on the other hand, may divide a number of times before it terminally differentiates.
These cells are known as the amplifying population. 

10. Adult Stem Cells
Adult stem cells (somatic stem cells) are responsible for tissue regeneration after injury or disease.
They are found in several parts of the body.
The bone marrow contains several kinds of stem cells:
Hematopoietic stem cells, forms all the types of blood cells in the body.
Bone marrow stromal cells generate bone, cartilage, fat, and fibrous connective tissue
The brain has also a small population of stem cells.

12. Can we induce stem cells to produce any cell?

13. Unanswered Questions http://stemcells.nih.gov/info/basics/basics4.asp
How many kinds of adult stem cells exist, where?
What are the sources of adult stem cells in the body?
What are the signals that regulate the proliferation and differentiation of stem cells that demonstrate plasticity?
Is it possible to manipulate adult stem cells to enhance their proliferation transplants can be produced?
Does a single type of stem cell exist—possibly in the bone marrow or circulating in the blood—that can generate the cells of any organ or tissue?
What are the factors that stimulate stem cells to relocate to sites of injury or damage?

14. Research Directions
Isolating stem cells and putting them in culture to generate an identical population of these cells (clones)
Inducing the stem cells to differentiate into certain cell types for transplantation.
Injecting stem cells to repopulate a depleted organ and survive there, without harming the host.
Manipulate the environment to influence the way stem cells differentiate.
Embryonic stem cells are pluripotent, but adult stem cells have only limited potencies.
Using adult stem cells is preferable, because of ethical issues, harvesting from the same patient reduces immune reactions to a transplant.
Understanding the mechanisms of differentiation and repair.
Use of stem cells to test new medications specific of humans

20. Differentiation of Cells during Embryogenesis

21. First event after fertilization
The zygote’s cytoplasm is not created equal.
Regionalization of the cytoplasm during mitosis.
Cytoplasmic determinants: based on the differential (asymmetric) localization of certain proteins and RNA’s
During the first few divisions of the zygote, the daughter cells are not identical.

22. P-granule segregation during the early embryonic divisions of the nematode Caenorhabditis elegans:
a)  A newly fertilized embryo with dispersed P granules. 
b)  P granules are localized to the posterior end of the zygote. 
c)  After the first division, P granules are present only in the smaller, posterior cell. 
d)  Another unequal division gives rise to a single cell containing P granules. 
e)  When the larva hatches, P granules are localized to the primordial germ cells. 

23. Differential Expression of Genes
Influence of the environment.
Interactions with neighboring cells, cell/cell interactions.
Diffusible signals.
Contact signals.
Expression of transcription factors.

24. Induction of a cell type by signaling mechanisms
One group of cells induces the development and differentiation of another group of cells

25. Morphogens Gradients
Determines the cell fate depending on exposure to a concentration of an agent.

26. Drosophila: An example of Morphogen diffusion

27. Sequential Induction
Release of a series of chemical signals, which induce cells nearby in a cascade of events.