Development Flashcards

1
Q

Why is gene expression important in development?

Why Drosophilia used

A
  • 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
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2
Q

How molecular biologist understand differentiation

A
  • compare mutants and normal cells

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

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3
Q

3 groups of genes that are important in embryo development

A
  1. Maternal genes/ egg polarity genes
  2. Segmentation genes
  3. Homeotic genes
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4
Q

Maternal/ Egg polarity genes

  • what it does
  • Drosophila follicle
A
  • 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.
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5
Q

Maternal/ Egg polarity genes

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

A
  • 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
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6
Q

Segmentation genes

A
  • 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
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7
Q

Segmentation genes - 3 subgroups and effect of mutation

A
  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
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8
Q

Homeotic Genes (hox genes)

A

-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

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9
Q

Hox genes in Drosophila - present in 2 complexes

A
  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
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10
Q

How do Hox Proteins work?

A
  • 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
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11
Q

Regulation of hox gene expression 2 groups

A
  • 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
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