1. Genes & Development
Packet #49
Chapter #21

2. Development

3. Introduction Development
The process by which descendents of a single cell specialize and organize into a complex organism
Development is accomplished via the use of stem cells.

4. Stem Cells
Stem cells
Have the ability to produce differentiated descendents, yet retain the ability to divide to maintain the stem cell population.
There are two categories of stem cells.

5. Stem Cells II Stem cells Totipotent stem cells Pluriopotent stem cells
Give rise to all cell types
Pluriopotent stem cells
Give rise to many, but not all, types of cells in an organism
Not capable of forming a functional organism.

6. Stem Cells III Stem cells Totipotent
Give rise to all types of stem cells
Pluriopotent
Gives rise to many, but not all, types of cells.

7. How do Cells Develop?

8. Introduction I
During the development of cells, cells must go through two phases.
Commitment
Cell Differentiation
Stem Cells
Commitment
Specification
Determination
Cell Differentiation

9. Introduction II Commitment Cell Differentiation
The official series of overt changes in cellular biochemistry, and function.
The cell commits to a certain fate.
Two stages
Specification
When cell is capable of differentiating autonomously (independent of the surroundings) when placed in a neutral environment (Petri dish or test tube)
Determination
When cell is capable of differentiating when placed into autonomously when placed into another region of the embryo.
Cell Differentiation
The development of specialized cell types

10. Differential Gene Expression
The cause of differences among various cell types.
Has three postulates
Every cell nucleus contains the complete genome established in the fertilized egg
Unused genes in differentiated cells are not destroyed or mutated, and they retain the potential for being expressed
Only a small percentage of the genome is expressed in each cell
Hence a small portion of RNA is synthesized specified for that cell type

11. Other Important Terms Nuclear Equivalence Totipotency
All nuclei, with a few exceptions, of differentiated somatic cells of an organism are identical to each other and to the nucleus of the single cell from which they descended.
Genomic rearrangement
Gene amplification
Totipotency
Capability of cells to direct the development of an entire organism

12. Categories of Genes

13. Genes & Development of Cells
Maternal Effect Genes
Segmentation Genes
Homeotic Genes

14. Maternal Genes

15. Maternal Effect Genes I
Genes expressed in the mother’s ovaries that produce mRNA’s that are ultimately placed in different regions of the developing egg
Establish the polarity of in the embryo.
Axis specification
Anterior vs. Posterior ends

16. Maternal Effect Genes II
The proteins produced from the mRNA transcribed from the maternal effect genes are types of morphogens.
Bicod & Hunchback proteins
Regulate the production of anterior structures of the embryos.
Nanos & Caudal proteins
Regulates the formation of the posterior structures of the embryos.
These proteins may behave as transcription factors that turn on HOX genes ultimately leading to the separation of the anterior from the posterior end
Morphogen
A soluble substance, chemical agent, that affects differentiation and specification of any totipotent cell.

17. Maternal Effect Genes III
Maternal Genes
Bicod & Hunchback proteins
Anterior regions
Nanos & Caudal proteins
Posterior regions

18. Segmentation Genes

19. Segmentation Genes
The proteins produced, as a result of the transcription of the Maternal Effect Genes, affect a class of genes called the segmentation genes.
Genes responsible for the transition from cell specification to cell determination.
In drosophila, divide the early embryo into a repeating series of segmental primordia along the anterior-posterior axis.
Divide the embryo into 14 parasegments.

20. Classes of Segmentation Genes
Gap Genes
Organization of regions
Pair Rule Genes
Divides segments into parasegments
Segment Polarity Genes
Maintains repeated structures within each segment
Gap Genes
Pair Rule Genes
Segment Polarity Genes

21. Classes of Segmentation Genes
Gap Genes
Respond to the concentrations of the material effect gene proteins
The first set of segmentation genes to act
Gap gene proteins define specific regions of the embryo
Begin organization of the body into anterior, middle and posterior regions
Gap gene proteins activate and repress the pair-rule genes

22. Classes of Segmentation Genes II
Pair Rule Genes
Proteins of pair-rule genes subdivide the broad gap gene regions, mentioned previously, into parasegments
Segment Polarity Genes
Responsible for maintaining certain repeated structures within each segment
Allowing for cell fates to be firmly established.

23. Homeotic Genes

24. Homeotic Genes--Fruit Flies
Regulated by gap, and pair rule, genes.
Responsible for specifying the “identity” of each segment
Wings
Legs

25. Review

26. Homework Assignment
What are the impacts of mutations in the Gap genes, pair rule genes and the homeotic genes.

27. Cloning
Nuclear Transplantation
Dolly The Sheep