1. Drosophila development begins with fertilization and cleavage stage divisions that partition the embryo into nuclei and cytoplasm. 2. Gastrulation then occurs, involving the formation of a germ band along the anterior-posterior axis as cells migrate inward. 3. Segmentation and organogenesis then establish the body plan, with segments forming along the axis and becoming specialized based on their position and interactions between maternal factors.

1. ANIMAL AND PLANT
ONTOGENETIC
DEVELOPMENT
MUSLIMA P. LIWALUG

3. D. MELANOGASTER
FERTILIZATION
Eggs are activated prior to fertilization
oocyte nucleus has resumed meiotic division
stored mRNAs begin translation
Eggs have begun to specify axes by the point of fertilization.
Sperm enter at the micropyle.
probably prevents polyspermy

4. SUPERFICIAL CLEAVAGE
Syncytial blastoder m stage
zygotic nuclei undergo 8 divisions
nuclei migrate to periphery
- karyokinesis continues
Cellular blastoderm stage
following division 13, oocyte plasma
membrane folds inward
partitions off each nucleus and associated
cytoplasm
constricts at basal end

5. SUPERFICIAL CLEAVAGE

6. GASTRULATION

7. GASTRULATION VENTRAL
FURROW

8. EARLY GASTRULATION

9. MID-GASTRULATION
fullest germ band extension:
just prior to segmentation
germ band cells:
form trunk
of the embryo
thorax and
abdomen

10. LATE GASTRULATION /
SEGMENTATION
organogenesis
segmentation
segregation of
imaginal discs
-
nervous system d
evelopment

11. ESTABLISHING THE
DROSOPHILA BODY PLAN
Segments form along the anteriorposterior axis, then become specialized.
Specification of tissues depends on their position along the primary axes.
A/P and D/V axes established by interactions between the developing
oocyte and its surrounding follicle cells

12. DROSOPHILA BODY PLAN –
EGG STAGE
Body axes are determined in the egg by distribution of maternal
mRNAs and proteins.
Translation leads to formations of patterning protein (e.g.
morphogen) gradient within the embryo.

13. OOCYTE FORMATION (A-P, D-
V AXES)

14. ANTERIOR – POSTERIOR
AXIS FORMATION

15. A-P AXIS: BICOID/ OSKAR/
NANOS
“posteriorized” follicles produce organized (
+/) microtubules
Nurse cells manufacture Bicoide and nanos
mRNA
deliver cytoplasm into oocyte
bicoid binds to dynein
moves to nongrowing () end of microtubules
Oscar mRN A forms
complex with kinesin I
moves toward growing (+) end of microtubules
Oskar binds nanos mRNA
retains nanos in posterior end

16. D – V AXIS (FURTHER
GURKEN EFFECTS)

17. D-V POLARITY

18. DISTRIBUTION OF DORSAL

19. ZYGOTIC PATTERNING
GENES

20. ANTERIOR-POSTERIOR
BODY PLAN

21. ANTERIOR SPECIFICATION -
1
Caudal specifies
posterior domain
Bicoid binds to caudal
3’UTR; prevents
translation

22. ANTERIOR SPECIFICATION -
2
Hunchback anterior
patterning

23. BICOID MUTANTS

24. MANIPULATING BICOID

25. POSTERIOR SPECIFICATION
- 1
Nanos trap:
Staufen allows
oskar translation
Oskar binds nanos
Nanos prevents hunchback
translation

26. POSTERIOR SPECIFICATION
-2

27. MODEL OF ANTERIOR-
POSTERIOR PATTERNING

28. TERMINAL SPECIFICATION -
1

29. TERMINAL SPECIFICATION -
2

30. SEGMENTATION GENES

31. ANTERIOR-POSTERIOR
BODY PLAN

32. ANTERIOR-POSTERIOR
BODY PLAN

34. SEGMENTS AND
PARASEGMENTS

35. SEGMENTS AND
PARASEGMENTS (ADULTS)

36. PAIR-RULE GENE
REGULATION

37. HOMEOTIC SELECTOR
GENES

38. HOMEOTIC GENE
EXPRESSION

39. ULTRABITHORAX MUTANT

40. ANTENNAPEDIA MUTANT

41. EIGHT EDITION
REFERENCE
SC O T T F. GI L B E RT