0. Practical, Life cycle, Procedure Flashcards
Life cycle of Drosophila melanogaster
adult embryo 1st instar larva 2nd instar larva 3rd instar larva prepupa pupa adult
Pattern formation
events that determine the spatial organization in the developing organism
Syncytium
the early embryo of many insects consists of 1 large cell with many nuclei
• consists of syncronius nuclei that divide at the same time
• ONLY NUCLEI DIVIDE
• nuclei move to the border of the cell and a cell membrane forms between = many individual cells
Syncytium v blastoderm
syncytium - 1 cell with many nuclei
blastoderm - cytoplasm divides to form many cells
You can already draw a fate map from…
the blastoderm stage
• cells know what they’re to do
Key events of embryogenesis occur in the
syncytial blastoderm stage
1. pole cell formation and migration
• pole cell = germline cells - pass on genetic info to next generation
2. determination of the anterior-posterior and dorso-ventral axes
3. segmentation = subdivision of the embryo along the anterior-posterior axis
Egg cytoplasm
is not uniform
Morphogens
chemicals in embryonic tissue that influence the movement and organization of cells
Morhpogens form a
concentration gradient
• high concentration in anterior
• low concentration in posterior
Bicoid
anterior to posterior gradient
• high concentration at the head
• low concentration at the tail
Bicoid is required for
the formation of the head and thorax
Bicoids with no anterior/posterior…
have 2 tails and no heads
Wild type bicoids
high concentration in anterior
low concentration in the posterior
High concentration in the middle
head in the middle
Several morphogen gradients
determine the cell fates along the anterior-posterior axis
• cells read concentrations of morphogens
Some animals have…
repeated units, including humans
In Drosophila a segmentation gene cascade results in
the formation of segments
Segmentation genes in Drosophila
morphogens to
gap genes to
pair-rule genes to
segment polarity genes
To detect the expression of a protein…
use antibody staining
here segmentation proteins
Transgenic
using wild type embryos +
additional bacterial genes
Lab constructs
promoter (not expressed) +
bacterial gene (lacZ)
• all express lacZ - especially in 7 stripes
In the embryo … is produced
the protein β-Galactosidase
- lacZ is the gene
- β-Galactosidase is the protein
β-Galactosidase is expressed in
endogenous ftz gene
2 step indirect antibody staining
- primary antibody directed against β-Galactosidase
- Incubate the secondary antibody to attache to the primary antibody
• this reacts with the stain to turn blue
4 steps (of embryos)
- rehydrate
- wash
- block
- antibody in primary antibody
While rehydrating and washing the embryos…
be careful not to remove the embryos
The Drosophila larva shows a complex pattern of
hairs and denticles
Mutant larvae/embryos show
different shapes
