1. Developmental Genetics
How Selective Gene Expression Determines the Developmental Fate of Specific Cells
-Chapter 17, pages Chapter 22, pages

2. Definitions
Determination = process of commitment of a cell to a particular fate
Differentiation = changes in cell shape and physiology associated with production of final cell type
Developmental field = a set of cells that together interact to form a developing structure
Morphogen = substance that specifies cell identity as a function of its concentration

3. Gene Expression
Differentiation depends upon the expression of a specific subset of genes.
Gene expression can be controlled at any level between transcription and activation of the protein product.

4. Control Points for Gene Expression in Eukaryotes
DNA
transcription
Transcriptional Control
RNA
Post-Transcriptional Control
processing
Translational Control
translation
Protein
Post-Translational Control

5. Developmental “Decisions”
Binary decisions
Separation of germ line from soma
Establishment of gender*
Choosing one fate from multiple options
Axis formation*
Segmentation*
Germ layer formation
Organogenesis

6. Ratio of Sex Chromosomes to Autosomes (X:A)
A Cascade of Events Affects Expression of Sex-specific Traits in Drosophila
Balance of Active
Transcription Factors
Presence or Absence
Of Sxl Protein
Sxl Protein Regulates Splicing of its own mRNA
Sxl Protein Regulates Splicing of tra mRNA
Tra Proteins Regulate Splicing of fru mRNA
Fru Proteins Control Sex-Specific Behavior
Tra Protein Regulates Splicing of Dsx mRNA
Dsx Proteins Activate
or Repress Transcription
of Sex-Specific Genes

7. Effects of X:Autosome Ratio

8. Transcriptional Regulation As a Result of X:Autosome Ratio
NUM:NUM dimers activate transcription of Sxl gene

9. Post-transcriptional Regulation of Sxl Protein Production

10. Post-transcriptional Regulation of Tra and Fru Protein Production
Sxl Protein Regulates Splicing of tra mRNA

11. Post-transcriptional Regulation: Alternative Splicing of Tra pre-mRNA
Sxl protein may block upstream 3’ splice site

12. Post-transcriptional Regulation of Fru Protein Production
Sxl Protein Regulates Splicing of tra mRNA
Tra Proteins Regulate Splicing of fru mRNA
Fru Proteins Control Sex-Specific Behavior as Transcriptional Regulators
Nervous system processing of information from antennae
Courtship Song Abdomen Movement

13. Post-Transcriptional Regulation of DSX Protein Production
Tra Protein Regulates Splicing of Dsx mRNA
Dsx Proteins Activate
or Repress Transcription
of Sex-Specific Genes

14. Summary of Protein Activities
NUM:NUM Homodimers
NUM = numerator
Sxl = Sex Lethal
Tra = Transformer
Dsx = Double sex
Fru = Fruitless
Transcriptional Activator
Splicing Regulator
Splicing Regulator
Dsx-M = Transcriptional Repressor Dsx-F = Transcriptional Activator
Fru-M and Fru-F are
Transcriptional Regulators

15. Applying Your Knowledge
Transcriptional Control
Post-Transcriptional Control
Which type of control is exerted to
Produce Tra Protein in Female Fruit Flies?
Keep the Sxl protein from being expressed in male fruit flies early in development?
Produce male and female-specific versions of the Fru gene product?

16. Applying Your Knowledge
Splicing Regulator
Transcription Factor
Which term best describes the action of
NUM:NUM homodimers?
Tra protein?
Sxl protein?

17. Development of Anterior-Posterior Body Axis in Drosophila

18. A Hierarchy of Gene Interactions Determines Segment Number and Identity Along the A-P Axis
Egg-polarity genes
Egg-polarity genes (Maternal)
Gap genes
Homeotic genes
Pair-rule genes
Zygotic genes
Segment-polarity genes

19. Distribution of Egg-polarity Gene Products

20. Action of Egg-polarity Genes Bicoid and Nanos
antpost
Transcriptional activator of anterior-specific genes, including hunchback, a gene needed of head and thorax development
Nanos
postant
Translational repressor of hunchback, preventing expression of anterior structures

21. Genes Influencing Segmentation along the A-P Axis

22. Action of Gap Genes
Gap gene products divide the body into broad zones for the formation of anteriorposterior segments.
Mutations show a loss of specific adjacent segments from the region where a gap gene is transcribed.
Krupple and Knirps encode transcription factors.

23. Action of Pair-Rule Genes
Pair-rule genes divide the body into a series of two-segment units.
Pair-rule gene mutations remove alternate segments, either odd or even.
Alternating activity of the genes Ftz (stained gray) and Eve (stained brown) is shown.
Fushi tarazu (Ftz) and Even-skipped (Eve) encode transcription factors.

24. Action of Segment-Polarity Genes
Segment-polarity genes regulate the organization of subsets of cells within a segment.
Segment-polarity mutations cause part of a segment to be deleted and replaced by a mirror image of a different part of the next segment.
Engrailed (EN) encodes a transcription factor.
Patched encodes a transmembrane protein.

25. Action of Homeotic Genes
Homeotic genes influence the identity of specific segments, controlling the development of segment-specific structures.
Mutations cause structures from one segment to develop in another.
T3 develops as T2 in the Postbithorax mutation.
Pbx is a cis-regulatory region controlling the action of Ubx on T3 development.

26. Clusters of Homeotic Genes
Affects Structures Developing in
Genes
Antennapedia Complex
Head and Anterior Thoracic Regions
Antennapedia Scr
Bithorax Complex
Abdomen and Posterior Thoracic Regions
Ultrabithorax Abdominal-A Abdominal-B

27. Scr
Antp
Ubx
Abd-B
Evidence for the correspondence between gene order and sequence of gene expression for the homeotic genes.

28. Evolutionary Conservation of Homeotic Gene Regions
Homeotic genes share a 180 base pair region called the homeobox.
The homeobox encodes a DNA-binding domain (homeodomain) with a helix-turn-helix structural motif.
Homeobox regions are found in clustered genes in the mouse.

29. Homeotic gene mutation resulting in
posterior location for anterior structures,
i.e. ribs from lumbar vertebrae.

30. Applying Your Knowledge
Splicing Regulator
Transcription Factor
Translation Regulator
Which term best describes the action of
The maternal product of the Nos gene?
The zygotic product of the Even-skipped gene?
The protein products of homeotic genes?