Stages of Development in Xenopus, Drosophila and Mouse Flashcards
What occurs in Xenopus early development? (amphibian)
- There’s a dark pigmented animal pole, and egg rich vegetal pole
- cell division occurs without increasing blastula size
- cells become progressively smaller
- blastomeres divide more rapidly than yolk cells
- radial cleavage occurs
1) sperm cell enters at animal pole
2) rotation of cortical cytoplasm reveals grey crescent region opposite sperm entry point
3) dorsal lip below grey crescent region
What occurs in Gastrulation in a Xenopus ( after cleavage ) ?
THE GENERATION OF ECTO/MESO/ENDODERM
1) Cells move into embryo, animal pole cells at dorsal lip of blastopore involute, causing future meso and endo dells to move
2) Archenteron (primitive gut) formed, displacing blastocoel
3) Gut surrounds yolk cells
4) Animal pole on ventral side of blastula envelop the vegetal pole cells by epiboly followed by involution through ventral lip of the blastopore
5) Head end formed at leading edge of mesoderm
What occurs in neurulation in a Xenopus?
- raised neural folds appear either side of neural groove
- folds move together form closed neural tube
What’re the stages of the Drosophila lifecycle?
1) Hundreds of fertilised eggs
2) Cleavage occurs , gastrulation embryo becomes specified into three separate body layers
3) Then goes into larval
What occurs in Gastrulation in the Drosophila?
- no nuclear/cell divisions
1) head region forms at anterior end distinguished by aphalic fold
2) ventral furrow appears on ventral surface
3) cellular movements occur
4) future mesoderm cells moved into embryo, by invagination tube of mesodermal cells then dissociate –> form a layer internally
5) at same time as gastrulation, germ band extension occurs
6) movement of ventral tissue around posterior end and onto dorsal side
7) future ant + post mid gut invaginate into embryo and fuse to form gut.
Formation of Drosophila Nervous System
- don’t form spinal cord but a form of it
1) Following invagination of future mesodermal cells, ventral furrow closes,
2) ectodermal cells either side of ventral furrow dissociate and start moving into position between external ectoderm and internal mesoderm
3) these cells become neuroblasts form nerve cord on ventral side
What occurs in first stage of Mouse Development following fertilisation?
1) pronuclei fuse
2) Fertilised oocyte divides forming two blastomeres
3) Division occurs by rotational cleavage (can cause odd no. of blastomeres
4) 8 cell compaction occurs, surround by zona pellucida
5) at 16 cell stage blastula called Monula
6) Blastocyst consists of inner cell mass surrounded by trophoblast cells and contains fluid filled cavity called blastocoele.
7) Blastocyst excapes from Zona Pellucida by secreted enzymes - called hatching.)
Implantation of Mammalian Embryos into uterine horns
- eggs released from both ovaries at the same time
- prior to implantation, inner cell mass forms epiblast and hypoblast (primitive endoderm)
- Primitive endoderm lines blastocoel forming yolk sac cavity
- epiblast cells line the forming amniotic cavity
- trophoblast cells that touch uterine wall continue to divide and invade uterus to form the syncytiotrophoblast
Gastrulation in mammalian (mouse) cell
- 3 layers derived from the epiblast
- signalling region called ‘the node’ @ posterior position
of epiblast layer - node –> primitive streak forming –> forms groove
- during gastrulation epiblast cells dissociate and migrate through primitive groove and node invading underlying prim endoderm cells, obliterating them.
- movement of cells via ingression forms 3 layers
- cells that move through become notochord
What do the Ectoderm (germlayers) in mammalian cells form?
Epidermis, brain, CNS
What do the Mesoderm (germlayers) in mammalian cells form?
Muscle, connective tissue, kidney, gonads, tissues or heart
What do the Endoderm (germlayers) in mammalian cells form?
Epithilium lining of gastrointestinal tracts, lungs, pancreas,
Neurulation in a mouse (mammalian)
1) ectodermal cells thicken forming neural plate (change caused by notochord)
2) Neural groove forms along midline of neural plate, neural folds either side of this groove
3) folds rise and move towards each other meeting and forming neural tube
4) Neural tube dissociates from ectoderm
5) other ectodermal cells form overlying epithelial sheet
The developing mammalian embryo divides by
rotational cleavage
During mammalian neurulation, neural folds form on the ectodermal layer of the trilaminar embryo, either side of the midline. The following processes then occur:
invagination occurs and a neural tube forms.
