lecture 3-4 Flashcards
what are the advantages of using drosophila as a model organism?
many of its genes are conserved in mice and humans
ex: engrailed - for prroper development of cerebellum
eyelesss/pax6: missexpressing the gene eyeless on the leg of drosophila leads to eye tissue structure appearing on the limb
what are the stages of embryonic development in drosophila?>
1) fertilization
2) after fertilization, cleavage occurs (so basically cells start dividing without an increase in volume, there is no cytokinesis, a thousand nuclei within the same cell)
3) This stage is now called SYNCYTIAL BLASTODERM (all stages up to this one have no zygotic activation)
SYNCYTIAL BLASTODERM = early step in the development of Drosophila where nuclei are located in the centre of the embryo and share the same cytoplasm
4) Outer membrane invaginates and cell boundaries start to form, resulting in a CELLULAR BLASTODERM - all cells seem to be pretty similar, except for pole cells which are the precursors of germ cells (they start migrating towards the position of the future gonads)
what are the 5 types of
what are the 5 classes of genes?
1) MATERNAL EFFECT GENES / EGG POLARITY GENES (introduced by the mother, are present before fertilization)
2) GAP GENES
3) PAIR-RULE GENES
4) SEGMENTATION GENES
5) SELECTOR GENES
give 2 examples of maternal effect genes
Bicoid - important for the ANTERIOR part of the body (with the help of the cytoskeleton and the way it is inserted in the egg by the mother, the RNAs are tethered to the anterior part of the embryo; it is present even before fertilization; it enters the nuclei and forms a nuclear gradient from anterior to posterior)
Nanos - important for the POSTERIOR part of the body
a special example is Hunchback, which is both zygotic and maternal
maternal Hb is equally distributed over the body, but zygotic Hb is activated by Bicoid above a certain threshold; Nanos prevents translation of maternal Hb by binding to the 3’ UTR of the gene that encodes for Hb, which results in accumulation of Hb at the anterior to midpart because of zygotic activation by Bicoid
So, Nanos prevents maternal Hb at posterior part
Another one is Caudal, inhibited by Bicoid so it basically accumulates where Bicoid levels are low: at the posterior part
GAP GENES
Gap genes are the first ones to be activated zygotically, they regulate each other’s expressions and are transient (=short-lived)
ex: Kruppel controlled by Hb
PAIR-RULE GENES
evenskipped and fushi tarazu = responsisble for formation of segments and parasegments of the body
eve is expressed in alternating bands
SEGMENTS = visible structures
PARASEGMENTS = defined by gene expression
what are the segmentation genes we have studied?
Engrailed, Wingless, Hedgehog
they produce diffusible proteins, are transiently expressed (they eventually disappear)
receptor of Hh = Patched, it is expressed in cells that do not express engrailed or Hh
The segmentation genes are responsible for the boundaries between parasegments.
how is the AP axis specified in Dorosphila?
It is specified pre-fertilization by Bicoid and Nanos that have a concentration gradient along the AP axis
Their RNAs move and concentrate in different parts of the cell through the cytoskeleton and through microtubules and motor proteins carrying them around
define a morphogen
Morphogens = extracellularly released molecules used by cells to communicate with each other
what is a HOMEOTIC TRANSFORMATION?
one segment or part of the body acquires another identity
what is EPIGENETICS?
EPIGENETICS = transfer of information, gene expression across cell divisions
ex: PolyComb Group = epigenetic regulator: they repress transcription by modifying tails of histones
- methylation
- ubiquitination
