Minitest 1 - Drosophila Mutants Flashcards
Orientation of Drosophila embryos
- dorsal = flat
- ventral = curved
- anterior = pointed
- posterior = blunt
Why is it difficult to identify all different stages?
some stages are shorter/longer than others
• embryogenes is fast - it takes only 13 hours from stage 1 to stage 17
What cell type is formed in stage 4?
pole cells
4 embryonic stages that are completed by stage 5
- pole cell formation
- cleavage divisions
- cellularization
- blastoderm nuclei migration
Physical features of stage 4
- yolk
- blastoderm nuclei
- pole cells
Physical features of stage 5
- blastoderm nuclei
- yolk
- visible border margin
Physical features of stage 7
- cephalic furrow
* proctodeal invagination (aka-ish posterior furrow)
Stomodeum vs proctodeal
stomodeum –> foregut
proctodeal –> hindgut
Pole cells become incorporated into the
posterior midgut and form a pocket visible as a groove
proctodeall invagination
What is the proctodeal invagination?
- a dorsal plate of blastoderm cells that carries the pole cells, tilts inward anteriorly and forms a pocket
- the pocket now contains the pole cells
- the pocket is called the proctodeal invagination
“Proctodeum”
part of the anal passage
3 folds that are clearly visible at stage 7
• cephalic furrow
• anterior furrow
• posterior furrow
(and proctodeal invagination)
AF PF PI CF
Physical features of stage 11
- clypeolabrum
- mesoderm
- stomodeal invagination
- yolk
The … forms the insect’s face
clypeolabrum - delimits the lower margin of the face
At stage 11 the … is the innermost layer of the germ band
mesoderm
• muscles derive from mesoderm
The stomodeal invagination listed under stage
10
• stage 10 lasts for 1h
• onset characterized by the appearance of the stomodeum which eventually gives rise to the foregutand its annexes
• the cells that form the stomodeum are internalized at the anterior ventral side of the embryo - the site of invagination is called the stomodeal invagination
Syncytium
a large cell containing multiple scattered nuclei
What do you call the early embryonic stage when cellularization takes place?
Blastoderm
The name of the outer egg shell
chorion
The name of the inner egg shell
vitalline membrane
Type of gene: Hunchback
- maternal effect gene
* gap gene
Type of gene: Kruppel
gap gene
Type of gene: Knirps
gap gene
type of gene: odd-skipped
pair-rule gene
Type of gene: wingless
segment polarity gene
Type of gene: patched
segment polarity gene
Formation of the dorso-ventral axis
Dorsal - the ventral morphogen
Dpp is expressed in
the dorsal ectoderm
Twist is expressed in
the ventral mesoderm
Hunchback is an
anterior morphogen
anterior –> posterior
…required for the formation of the anterior part of the embryo
Bicoid AND Hunchback
Hunchback missing
Hunchback cuticle phenotype
• still has bicoid –> still has head
• 3 thoracic segments missing
(most anterior structures co-depend on bicoid)
• shorter - only see the abdomen and head
• head involution is incomplete
• fusion of A7 and A8
Head involution
during late embryogenesis the head jis folded back into the embryo
In hunchback mutants the dorsal part of the embryo/larva is missing
FALSE
In hunchback mutants head involution is affected
TRUE
In hunchback mutants abdominal segents 7 and 8 are fused
TRUE
In hunchback mutants thoracic segments 1 to 3 are missing
TRUE
In hunchback mutants denticle belts are dorsally expanded
FALSE
Gap gene expression patterns are
- extablished by maternal morphogens
- maintained by mutual repression
- high levels of Bicoid and Huncback activate Giant
- low levels of Hunchback activate Kruppel
- Caudal activates Knirps and Giant
High levels of Bicoid and Hunchback activate
Giant
bicoid and hunchback = gap genes
Low levels of Hunchback activate
Kruppel
Hunchback = gap gene
Caudal activates
Knirps and Giant
Kruppel is expressed in the area which will develop into
T1 - A5
Knirps is expressed in the area which will develop into
A2 - A5
Kruppel mutant embryos
gap genotypes
deletions between T1 and A5
see few abdominal
Knirps mutant embryos
gap phenotypes
A2 to A5 are affected
In Kruppel mutants all abdominal segments are deleted
FALSE
In Kruppel mutants all thoracic segments are deleted
TRUE
In Kruppel mutants the segments betwen T1 and A5 are deleted
TRUE
In Kruppel mutants abdominal segments A1 to A5 are fused
FALSE
In Kruppel mutants thoracic segments T1 to T3 are fused
FALSE
In knirps mutants abdominal segments are deleted
TRUE
In knirps mutants denticle belts are dorsally expanded
FALSE
In knirps mutants all cells form dorsal cuticle (ie hairs)
FALSE
In knirps mutants T1 to T3 are missing
FALSE
In knirps mutants abdominal segments can be fused
TRUE
The pair-rule gene expression patterns divide the embryo into
precursors of the segmental units
In odd-skipped mutants
pair-rule
• every other segment is missing • have 2468 but no 1357 (thoracic misses even) • ventral denticles in anterior • deletion of all or half of the denticle belts in odd-numbered segments
In odd-skipped mutants, the denticle belts of … are present
denticle belts of
T1, T3, A2, A4, A6, and A8 are present
In odd-skipped mutants denticle belts in odd numbered segments can be completely absent
TRUE
In odd-skipped mutants half of the denticle belts in odd numbered segments can be absent
TRUE
In odd-skipped mutants even-numbered denticle belts can be completely absent
TRUE
In odd-skipped mutants the thoracic denticle belts are fused
FALSE
In odd-skipped mutants abdominal denticle belts are fused
FALSE
In early embryos, there are different gene expression domains
(Gap –> segment polarity)
segment polarity genes
• give 14 stripes (engrailed and wingless)
• anterior –> posterior identity of each segment
get morphogenically visible segments
The expression of Wingless and Engrailed is maintained by
interactions between the products of these genes
Maintenance of wingless and engrailed expression by
mutual regulation
Wingless mutant
• gradient of expression in segment • anterior hairs in denticle belt • remove wingless = smaller • form naked cuticle --> get only denticle (no gap = HAIRY EMBRYO)
Wingless and Hedgehog gradients are required for
the different fates of the epidermal cells
Naked cuticle in area of
wingless expression
• fusion of denticle belt
In wingless mutant embryos the denticle belts are dorsally expanded
FALSE
In wingless mutant embryos the first abdominal segment is enlarged
FALSE
In wingless mutant embryos the denticle belts are fused
TRUE
In wingless mutant embryos head defects can be observed
TRUE
In wingless mutant embryos the naked cuticle between denticle belts is reduced or absent
TRUE
Formation of the dorso-ventral axis requires
Dorsal, the ventral morphogen
Dorsal is only expressed in the
ventral part of the embryo
Dorsal protein - wild-type
Dorsal in ventral nuclei –> both dorsal and ventral
Dorsal protein in all nuclei
ventralized embryo
Dorsal switches…
- TWIST on in ventral
* DPP off in dorsal
Dorsal protein activates and represses different
zygotic genes
depending on twist (?) nuclear concentration
Genes downstream of Dorsal activate
other genes that further subdivide ventral cell fate
Dpp cuticle phenotype
all structures above the H46 line are absent in the mutant embryos/larvae
Dpp mutant - weak phenotype
deletions of dorsal-anterior structures
Dpp mutant - strong phenotype
dorsal expansion of denticle belts up to denticle belts encircling whole embryo
Dpp - need dorsal structures, repress –>
dorsal structures absent = expanded ventral structures
In decapentaplegic mutants dorsal parts of the embryo/larva are missing
TRUE
In decapentaplegic mutants the first abdominal segment is enlarged
FALSE
In decapentaplegic mutants denticle belts are dorsally expanded
TRUE
In decapentaplegic mutants there are deletions between T1 and a5
FALSE
In decapentaplegic mutants abdominal segments are fused
FALSE
Twist mutant phenotype
- ventral structures are missing = dorsalized
- no extension and return of germ band
- so grow and eggshell prevents extension = twisted
