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Midterm

MCD BIO 138 Study Guide - Midterm Guide: Signal Transduction, Oogenesis, Microtubule


Department
Molecular, Cell, and Developmental Biology
Course Code
MCD BIO 138
Professor
karenlyons
Study Guide
Midterm

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Review Questions for Midterm
Oogenesis in Drosophila:
1. How do older egg chambers influence acquisition of polarity in younger egg
chambers?
2. What is the first clear asymmetry in the Drosophila egg chamber
3. What is the role of Gurken in defining the AP and DV axes of the oocyte?
Gurken in A/P is deposited in the eggs by the nurse cells. translated in egg before
fertilization and secreted before binding to torpedo receptors on the adjacent follicle
cells.
-this activates a signal transduction pathway in follicle cells
- The follicle cells send a signal back to oocyte that causes reorganization of
microtubules in the oocyte
-Gurken in the D/V is the cause of microtubule reorganization.
- deposited by Nurse cells moves to the region around the nucleus. Gurken
mRNA is translated here and creates a new localized source of Gurken protein
- signals to the adjacent follicle cells to specify them as dorsal.
- signaling to dorsal follicle cells leads to differences in gene expression in
dorsal vs ventral follicle cells.
Maternal genes
1. What are the maternal genes we discussed in class that control:
A/P axis: Follicile cells
D/V axis: Gurken mRNA
2. Which of these maternal genes act as transcription factors and which as secreted
factors?
3. Where are the mRNAs/proteins encoded by these genes localized before and after
fertilization?
Prior to fertilization:
cell-cell interactions (oocyte-follicle cells) establish A/P axis:
role of Gurken/Torpedo in triggering microtubule rearrangements leading
to localization of maternal mRNAs along A/P axis of embryo
D/V axis:
role of Gurken/Torpedo in localized production by ventral follicle cells of a
ligand that will signal back to oocyte on ventral side
After fertilization:
A/P axis: Bicoid, etc will be translated and will regulate expression of zygotic
genes

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D/V axis: Toll signaling on ventral side of embryo leads to a gradient of nuclear
localized Dorsal transcription factor
Zygotic genes Dpp, Sog, and Tolloid are regulated by Dorsal and encode secreted
factors that complete the patterning of the DV axis
4. How is the gradient of DPP activity that generates the DV axis in Drosophila created?
What are the functions and expression patterns of Sog and Tolloid, and how do they
impact the DPP gradient?
Sog: inhibitor of DPP; binds to DPP and prevents DPP from binding to its receptor
- Drosophila homolog of vertebrate chordin
Tolloid: protease that cleaves and inactivates Sog. This allows DPP to bind to its
receptor
5. What types of experiments were used to define the role of Toll signaling in regulating
expression of these genes? What were the results?
Toll is a cell-surface receptor.
•Toll mRNA is
uniformly distributed
in unfertilized egg.
•Toll receptor protein
becomes uniformly
distributed in egg
membrane at fertilization
Toll signaling leads to a gradient of nuclear-localized DORSAL transcription factor in the
embryo.
Before Toll signaling: Dorsal
protein is in cytoplasm
After Toll signaling: Dorsal enters nucleus on ventral side of the embryo
Toll signaling on the ventral side of the embryo cleaves Cactus to allow Dorsal to enter
the nuclei
Zygotic genes
1. Define each term and give one example of each
zygotic lethal gene: phenotype of the embryo depends on its own genotype, zygotes
lethal gene affecting embryonic development must be transcribed during
embryogenesis.
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maternal effect gene: transcribed during oogenesis, gene products play an important
role in embryogenesis, genotype of mom determine phenotype of dad
gap gene: cause deletions of large regions along the A/P axis of the Drosophila embryo
pair rule gene: cause deletions or abnormalities in each pair of segments.
segment polarity gene: cause deletions or abnormalities within every segment
Homeotic gene:
2. What are the basic functions of gap, pair-rule, segment polarity, and homeotic
genes? in your example, describe the type of phenotype that is obtained for a loss of
function mutation in these genes)
Gap gene: controlled by maternal genes and other gap genes
Act downstream of maternal effect genes to pattern the A/P axis
Pair rule genes: controlled by the expression of gap genes
-divides the embryo into discrete segments/ parasegments
-encodes transcription factors and expressed inseven stripes
-loss of one parasegment created results in destruction of the others
-stripes are individually controlled by both maternal and gap genes
-Segment polarity/segmentation genes define A/P identity to cells within each
parasegment
Expression is controlled by pair-rule genes
•Are expressed in a portion of each segment (usually one stripe of cells in each
parasegment)
Segment polarity genes:
•establish boundaries between parasegments
•define A/P identity of the cells within each parasegment
3. What is the hierarchy for the maternal and zygotic genes and what experiments
demonstrate this hierarchy? What are the results of the experiments?
on basis of patterns of gene expression in mutant embryos:
mutant gene alters expression of genes
acting below it, but not above it, in the …hierarchy
hb, Kr gap genes
ex: bcd maternal gene
Example: expression of some gap genes is abnormal in bcd mutant embryos
-
4. How is the Dorsal gradient established? Is Dorsal a morphogen? Why or why not?
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