Drosophila Axis Determination
Many genes that determine our own axis are ac4ve in drosophila
Drosophila as Model Organisms
- Rela4vely short life cycle and genera4onal turnover
- Large numbers of offspring
- Well characterized gene4cally
o Understand how to set up mutagenesis screens
o Easy to map muta4ons
o Isola4on of mutants is rela4vely easy
- Easy to maintain in a lab
- Easy to gain ethics clearance
- Mul4cellular organism à good for developmental studies
o Different axes
o Organ development
- Landmark features that allow for mutant iden4fica4on defec4ve in anterior vs
posterior and dorsal vs ventral
o External exoskeleton structures are built from underlying epidermal cells
§ Hairs, den4cles, indenta4ons, cu4cle structures
§ Dorsal surface = covered in hairs
§ Ventral = dis4nct den4cle belt for each segment
How to iden4fy and analyze mutant gene4c makeup:
- Characteriza4on of mutant phenotypes
o Important for characterizing which structures are affected by a par4cular
muta4on
- Nucleo4de sequence of clone
o Subsequent determina4on of amino acid sequence à informa4on on protein
func4on
- Spa4al and temporal paPerns of expression at RNA level à in situ hybridiza4on
o At protein level à immunocytochemistry
- Gene4c experiments à how genes interact
Drosophila and the animal kingdom
- Humans ≠ new genes compared to fruit flies
- Drosophila à 1 gene
- Humans à mul4gene families for the drosophila equivalent
Development in Drosophila
- Takes 24 hours for a fer4lized egg to develop into a segmented fully differen4ated
maggot
- Oocyte matura4on in females
- Fer4liza4on in uterus
- Fer4lized eggs are laid
o Syncy4al blastoderm (13 divisions) à first 4 hours of development
§ No cell membranes separa4ng mul4ple nuclei
, § A]er 7th division, 15 nuclei to the posterior of the pole and rest of 128
nuclei migrate to anterior pole à become pole cells (become germ
cells of the embryo)
o Cellular blastoderm (a]er 13th cell division)
§ Each nucleus is surrounded by a cell membrane
o Segmenta4on
§ During gastrula4on will see forma4on of cephalic furrow that will be
where the head forms
- Eggs hatch
- 1st instar larva
- 2nd instar larva
- 3rd instar larva
- Pupa
- Adult fly
, Early Development Cycle (first 4 hours)
- 13 cell divisions occur within a common cytoplasm
- 9th division à appearance of pole cells in the posterior (landmark in development)
o Nuclei migrate to periphery of embryo: syncy4al blastoderm
§ Common cytoplasm
§ TFs at a local source can diffuse and all the nuclei can receive the
same signal
th
- A]er 13 division à cell membranes ingress between nuclei to form cellular
blastoderm
Establishment of anterior/posterior vs dorsal/ventral
- Bilateral symmetry
- Key structures for anterior vs posterior
o Acron (head à forms from cephalic furrow that marks gastrula4on)
§ Different segments
• CL, PC, O, D, Mx, Mi, Lb
o 3 thoracic segments
o 8 abdominal segments
o Telson
o Anal plate
o Filzkoper at posterior
- Can iden1fy structures based on external cu1cle structure, pa9erns of bristles and den1cles
and internal organiza1on
- Along dorsal ventral axis:
o Mesoderm, ventral ectoderm, dorsal ectoderm and amnioserosa
§ Mesoderm à internal so@ 1ssue (muscle and connec1ve 1ssue)
§ Ventral ectoderm à neural 1ssue and ventral epidermis
§ Dorsal ectoderm --. Epidermis
§ Amnioserosa à extra-embryonic membrane that is sloughed off during
embryonic development
Iden4fica4on of mutants defec4ve in anterior-posterior paPerning – maternal effect and
zygo4c effect genes
- Maternal effect = genes expressed in mother, mRNA transcripts passed into
developing oocyte and transcribed in nurse cells in the ovary of the mother
o Phenotype of embryo dependent on maternal genotype
§ Muta4ons will be picked up by embryo
§ Phenotype is independent of paternal genotype
§ Recessive muta,on only produces a mutant when mother = mutant
homozygote
§ Bicoid, nanos
- Zygo4cally ac4ng = genes expressed in developing embryo
o Kruppel, fushi tarazu, even-skipped
o Recessive muta4ons in zygo4c genes à express if mutant homozygote
Many genes that determine our own axis are ac4ve in drosophila
Drosophila as Model Organisms
- Rela4vely short life cycle and genera4onal turnover
- Large numbers of offspring
- Well characterized gene4cally
o Understand how to set up mutagenesis screens
o Easy to map muta4ons
o Isola4on of mutants is rela4vely easy
- Easy to maintain in a lab
- Easy to gain ethics clearance
- Mul4cellular organism à good for developmental studies
o Different axes
o Organ development
- Landmark features that allow for mutant iden4fica4on defec4ve in anterior vs
posterior and dorsal vs ventral
o External exoskeleton structures are built from underlying epidermal cells
§ Hairs, den4cles, indenta4ons, cu4cle structures
§ Dorsal surface = covered in hairs
§ Ventral = dis4nct den4cle belt for each segment
How to iden4fy and analyze mutant gene4c makeup:
- Characteriza4on of mutant phenotypes
o Important for characterizing which structures are affected by a par4cular
muta4on
- Nucleo4de sequence of clone
o Subsequent determina4on of amino acid sequence à informa4on on protein
func4on
- Spa4al and temporal paPerns of expression at RNA level à in situ hybridiza4on
o At protein level à immunocytochemistry
- Gene4c experiments à how genes interact
Drosophila and the animal kingdom
- Humans ≠ new genes compared to fruit flies
- Drosophila à 1 gene
- Humans à mul4gene families for the drosophila equivalent
Development in Drosophila
- Takes 24 hours for a fer4lized egg to develop into a segmented fully differen4ated
maggot
- Oocyte matura4on in females
- Fer4liza4on in uterus
- Fer4lized eggs are laid
o Syncy4al blastoderm (13 divisions) à first 4 hours of development
§ No cell membranes separa4ng mul4ple nuclei
, § A]er 7th division, 15 nuclei to the posterior of the pole and rest of 128
nuclei migrate to anterior pole à become pole cells (become germ
cells of the embryo)
o Cellular blastoderm (a]er 13th cell division)
§ Each nucleus is surrounded by a cell membrane
o Segmenta4on
§ During gastrula4on will see forma4on of cephalic furrow that will be
where the head forms
- Eggs hatch
- 1st instar larva
- 2nd instar larva
- 3rd instar larva
- Pupa
- Adult fly
, Early Development Cycle (first 4 hours)
- 13 cell divisions occur within a common cytoplasm
- 9th division à appearance of pole cells in the posterior (landmark in development)
o Nuclei migrate to periphery of embryo: syncy4al blastoderm
§ Common cytoplasm
§ TFs at a local source can diffuse and all the nuclei can receive the
same signal
th
- A]er 13 division à cell membranes ingress between nuclei to form cellular
blastoderm
Establishment of anterior/posterior vs dorsal/ventral
- Bilateral symmetry
- Key structures for anterior vs posterior
o Acron (head à forms from cephalic furrow that marks gastrula4on)
§ Different segments
• CL, PC, O, D, Mx, Mi, Lb
o 3 thoracic segments
o 8 abdominal segments
o Telson
o Anal plate
o Filzkoper at posterior
- Can iden1fy structures based on external cu1cle structure, pa9erns of bristles and den1cles
and internal organiza1on
- Along dorsal ventral axis:
o Mesoderm, ventral ectoderm, dorsal ectoderm and amnioserosa
§ Mesoderm à internal so@ 1ssue (muscle and connec1ve 1ssue)
§ Ventral ectoderm à neural 1ssue and ventral epidermis
§ Dorsal ectoderm --. Epidermis
§ Amnioserosa à extra-embryonic membrane that is sloughed off during
embryonic development
Iden4fica4on of mutants defec4ve in anterior-posterior paPerning – maternal effect and
zygo4c effect genes
- Maternal effect = genes expressed in mother, mRNA transcripts passed into
developing oocyte and transcribed in nurse cells in the ovary of the mother
o Phenotype of embryo dependent on maternal genotype
§ Muta4ons will be picked up by embryo
§ Phenotype is independent of paternal genotype
§ Recessive muta,on only produces a mutant when mother = mutant
homozygote
§ Bicoid, nanos
- Zygo4cally ac4ng = genes expressed in developing embryo
o Kruppel, fushi tarazu, even-skipped
o Recessive muta4ons in zygo4c genes à express if mutant homozygote
