Lecture 6: What controls development in animals Flashcards
Key stages of development (reviewed)
- fertilisation
- cleavage
- Gastrulation
- organogenesis
- morphogenesis
morphogenesis:
cell differentiation and growth to form the complex adult shape
development is controlled by:
- the cytoplasm
- genes
- the external environment
Nuclear DNA does 2 things:
- replicates itself
- makes proteins (by transcription of RNA)
what controls early embryonic development?
- Nuclear DNA replication
- Enzymes and proteins are provided by the cytoplasm
- Metabolic cycles and instructions for driving cell division are controlled by the cytoplasm
- Zygotic cytoplasm comes from the mother, so early development is under maternal control
Genomic activation is the
transition from eternal control to embryo control
the timing of genomic activation…
VARIES
- pigs & rats: 4-8 cell embryo
- humans & cattle: 8 cell embryo
- frogs: 3,000-4,000 cell embryo
differentiation is the…
commitment of a cell to a particular fate, prior to this, cells are totipotent
differentiation results from..
differential gene expression.
-differential gene expression is influenced by the cytoplasm & the extracellular environment
Developmental control: the cytoplasm
- no information is lost in the early stages of embryonic development (genomic equivalence)
- the cytoplasm controls the fate of the nucleus
- cytoplasmic factors in the gray crescent are necessary for development
chemical single are involved in cell differentiation:
1) CYTOPLASMIC SEGREGATION - a factor is unequally distributed in the cytoplasm and ends up in some daughter cells but not others
2) INDUCTION - a factor is secreted by some cells to induce other cells to differentiate
cytoplasmic segregation:
- Dividing cells receive unequal amounts of materials that were distributed unevenly in the zygote
- These differences in cytoplasmic make-up cause differentiation of cells
(primary) induction: in amphibians
cells movie over the dorsal lip of the blastopore (Spemann organiser) induce overlying ectoderm to form neural tissue
(primary) induction: in birds
cells moving over Hensons node are induced to form the Central Nervous System
(secondary) induction in the vertebrate eye
- developing forebrain and surface tissue work together
- surface tissue expands forms lens placode tissue
- -optic cup formed from developing forebrain, developing lens folds inside optic cup
- developing sense forms a circle = LENS + cornea lies over top
how do cells ‘know’ where they are in an animal
by interpreting POSITIONAL INFORMATION
positional information is given by..
the concentration gradient of a morphogen
a signal is considered to be a morphogen if//
- it directly affects target cells
- different concentration cause different effects
in hands: morphogen concentration and fingers & thumbs
- the cells that become the bones & muscles of a limb receive positional information, then organise appropriately.
- Cells at the base of the bud make a morphogen (BMP2) whose gradient determines the anterior–posterior axis of the limb
- highest dose of BMP2 > thumb
- smallest dose of BMP2 > little finger
morphogen in hands
BMP2
what is genomic imprinting:
In mammals, some development genes are active only if they come from a sperm, others only if they come from an egg.
- -male-male zygotes don’t produce an embryo
- -female-female zygotes don’t form a placenta
Prader-Willli Syndrome:
deletion on paternal chromosome 15
Angelman Syndrome
Deletion on maternal chromosome 15
Segmentation genes: what and how many
- influence the number, boundaries & polarity of the body segments
- 4
