CHAPTER 11 The Control of Gene Expression Modules 11.12 – 11.14

11.12 Cascades of gene expression and cell-to-cell signaling direct the development of an animal A cascade of gene expression involves genes for regulatory proteins that affect other genes It determines how an animal develops from a fertilized egg

Head of a normal fruit fly Head of a developmental mutant Mutant fruit flies show the relationship between gene expression and development Eye Antenna Some mutants have legs where antennae should be Head of a normal fruit fly Leg Head of a developmental mutant Figure 11.12A

• Development of head-tail polarity in fruit fly EGG CELL WITHIN OVARIAN FOLLICLE Egg cell Egg protein signaling follicle cells 1 Follicle cells Gene expression in follicle cells Follicle cell protein signaling egg cell 2 Localization of “head” mRNA 3 “Head” mRNA Figure 11.12B

FERTILIZATION AND MITOSIS ZYGOTE EMBRYO Translation of “head” mRNA Gradient of regulatory protein 4 Gene expression Gradient of certain other proteins 5 Gene expression Body segments 6 Figure 11.12B

EMBRYO Body segments 6 LARVA Gene expression ADULT FLY 7 Head end Tail end Figure 11.12B

Cell-to-cell signaling is important in 11.13 Signal-transduction pathways convert messages received at the cell surface into responses within the cell Cell-to-cell signaling is important in development coordination of cellular activities

A signal-transduction pathway that turns on a gene SIGNALING CELL Signal molecule 1 Plasma membrane Receptor protein 2 (1) The signaling cell secretes the signal molecule TARGET CELL (2) The signal molecule binds to a receptor protein in the target cell’s plasma membrane Figure 11.13

(4) The last relay protein activates a transcription factor SIGNALING CELL Signal molecule 1 Plasma membrane Receptor protein 2 (3) Binding activates the first relay protein, which then activates the next relay protein, etc. 3 TARGET CELL Relay proteins 4 Transcription factor (activated) (4) The last relay protein activates a transcription factor Figure 11.13

(5) The transcription factor triggers transcription of a specific gene SIGNALING CELL Signal molecule 1 Plasma membrane Receptor protein 2 (5) The transcription factor triggers transcription of a specific gene 3 TARGET CELL Relay proteins 4 Transcription factor (activated) (6) Translation of the mRNA produces a protein NUCLEUS DNA 5 Transcription mRNA New protein 6 Translation Figure 11.13

11.14 Key developmental genes are very ancient Homeotic genes contain nucleotide sequences called homeoboxes are similar in many kinds of organisms arose early in the history of life

Fruit fly embryo (10 hours) Fruit flies and mice have similar homeotic genes (colored boxes) The order of homeotic genes is the same The gene order corresponds to analogous body regions Fly chromosomes Mouse chromosomes Fruit fly embryo (10 hours) Mouse embryo (12 days) Adult fruit fly Adult mouse Figure 11.14