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Flashcards in Development Deck (11):
1

Why is gene expression important in development?

Why Drosophilia used

-single cell differentiates into many different organs, tissues, limbs etc.
-causes cells to perform different functions

-Drosophilia used to study development because of;
-its v. short life cycle
-Egg develops into complete adult in 9 days

2

How molecular biologist understand differentiation

-compare mutants and normal cells

-Mutants whose embryos have problem in development & identify mutated gene or missing products in mutants

3

3 groups of genes that are important in embryo development

1. Maternal genes/ egg polarity genes
2. Segmentation genes
3. Homeotic genes

4

Maternal/ Egg polarity genes

-what it does

-Drosophila follicle

-Fate of cell largely determined by its position in the egg
-cells at anterior end develop into head structures
-cells at posterior end develop into legs or arms
*there is a specific way things develop

-Drosophilia follicle contains outer surface of follice cells that surround nurse cells that are in close contact w/ oocyte
-nurse cells contected by cytoplasmic bridges to each other and to the anterior end of the oocyte. Follicle cells somatic; nurse cells and oocyte are germline in origin.

5

Maternal/ Egg polarity genes

-3 genes that determine anterior, posterior, dorsal and ventral ends

-Dorsal protein in nuclei helps determine dorsal - bentral axis of drosophilia embryo
-dorsal protein conc. in nuclei on ventral surface (does diffuse across cell)
-Bicoid and Nanos proteins determine the anterior-posterior axis in Drosophila embryo
-Bicoid: localised at anterior end of egg
-Nanos products located at posterior end of drosophilia embryo

6

Segmentation genes

-embryo will cosist of 3 thoracic and 8 abdominal segments in addition to head and tail structures
-Mutations in segmentation genes lethal -> causes improper segmentation and embryo dies before maturity

*total of 30 segmental genes - divided into 3 subgroups
1. Gap genes
2. Pair Rule Genes
3. Segment polarity genes

7

Segmentation genes - 3 subgroups and effect of mutation

1. Gap genes: mutation causes elimination of anterior segments
2. Pair-Rule genes: mutation causes deletion of even-numbered segments
3. Segment-polarity genes: mutations causes posterior half of each segment to be replaced by mirror image of anterior half an adjacent segment

8

Homeotic Genes (hox genes)

-responsible for the development of body parts
Homoios - something has changed to something else
-mutations in any one of these genes causes one body part to develop as another
-Each gene has a region of homology, called Homeobox (is 180bp in length)
-codes for a DNA binding domain (Homeodomain) that is similar in all hox gene products
-homeodomain present near C-terminus and 80% conserved in all Hox proteins

9

Hox genes in Drosophila - present in 2 complexes

1. antennapedia complex (has 5 genes)
-homeotic genes confer identity on the most anterior segments of the fly
-genes vary in size and are interspersed w/ other genes
2. Bithorax complex (contains 3 hox genes)
-proceeding from left to right each homeotic gene in complex acts upon a more posterior region of the fly
-formation of a compartment that requires the gene product(s) expressed in previous compartment plus a new function coded by next gene along cluster

10

How do Hox Proteins work?

-Homeodomain is a helix turn helix motif, a DNA binding region
-provides specificity in DNA binding
-can act as an activator or a repressor (depends on a.a. seq. and N terminus & other proteins interacting with it)
-Hox proteins frequently found complexed with other proteins
-hetrodimer formation extends range of regulatory activities of Hox proteins

11

Regulation of hox gene expression 2 groups

-Different hox proteins required at various stages of development
-tight control is important for normal development
-genes controlling hox genes placed in 2 groups;
1. Polycomb group (pc-G) - Pc-G proteins act by recognizing a DNA region called polycomb response element - their binding to target DNA causes REPRESSION of nearby genes
2. Trithorax group (Trx-G): are activators of hox genes - their binding to DNA maintains chromatin in transcriptionally active state