Axes of Development Flashcards
What are the key stages of development?
Gamete formation: Sperm and egg form and mature
Fertilisation: Egg and sperm fusion
Cleavage: Zygote subdivides, determinants partitioned into blastomeres
Gastrulation: Germ layers form
Organogenesis: Body organs form, cells interact and differentiate.
Growth: Organs increase in size, adult body form attained.
What do morphogens do in cells?
They regulate which genes are switched off during development to allow for specialization.
How do cells ‘know’ where to grow and develop?
Cells identify and respond to their position in developmental fields.
How is development homologous between animals?
The genes that control development of homologous structures are exactly the same. The differences are explained by genetic changes within these genes.
What is the role of PAX genes?
They encode transcription factors important in early development and tissue specification. (eg Pax6 is a gene required for eye development across many species.) Mutations in these genes are lethal when homozygous and cause defects in eye formation when heterozygous.
What happens when we express a mouse Pax6 gene in a fly?
It doesn’t result in mouse eye in humans. Instead it results in Drosophila developing it’s own eye-development circuitry.
What other genes are deeply homologous and responsible for limb development in both humans and flies?
Hox genes.
What happens in early embryo which allows for specialization of cells regionally?
Segmentation of the body. The segments are restricted in what they can be based on position. These are called homeobox genes or hox (homeotic genes in flies)
What is morphogenesis?
Development of a single cell into a whole organism.
What is differentiation?
Cells become specialized in function and structure
How are specialized cells formed?
By a hierarchy of developmental cues and decisions.
Various cell types arise from intra/extra cellular conditions created in preceding stages.
Interactions/decisions become more and more restrictive in their developmental fate as the cells become more specialized.
How do embryonic cells acquire their fates at the molecular level?
They are arranged into basic axes according to their body plan.
What are the features of developmental decisions?
They are made at specific times during development
Many are binary
Most are irreversible
Many involve groups of cells rather than single cells.
What do most decisions do?
They involve changes in transcription. They are important for cells to commit to a fate.
How are the axes established?
In animals decisions are made to:
Establish anterior-posterior and dorsal-ventral axes
Subdivide anterior-posterior axis into segments
Subdivide dorsal-ventral axis into germ layers
Produce various tissues and organs.
How can gene expression be identified in developing embryos?
Via the use of a process called in situ hybridisation where antibodies are made against the mRNA and then broken down by enzymes to become fluorescent and visible under light microscope. Another way is using fluorochrome conjugated antibodies. *THIS IS NOT A LEARNING OUTCOME
Why is the drosophila model used to understand development?
Many developmental genes in vertebrates were identified in Drosophila first Demonstrates general principles of development conserved across animals Experimentally very powerful Much less complex than mammalian development.
How are mutations induced in drosophila?
EthylMethane Sulfonate (EMS) it induces point mutations.
How does EMS work?
Causes specific mispairing (Transition mutation (T replaces C and results in G-T), it is an alkylating agent and adds ethyl.
How do the germ layers form?
First cleavage= multiple rounds of rapid cell division to create > 100 cells called the blastula.
Single layer blastula is reorganised into three-layered structure called the gastrula. Germ layers: Meso-, Endo-, Ecto-derm.
Give an example of homologous structure shared among humans, birds and other veterbrates.
Our limbs are modifications of a structure shared by common ancestor of vertebrates, homologous to bird wings.
Homologous structures often arise through homology at the gene level… same genes control development of arms in humans & wings in birds.
Why is the drosophila melanogaster or the fruit fly a popular developmental model?
- animal
- diploid
- many progeny produced
- amenable to mutagenesis, many developmental mutants made
- easy to study mutants by inspecting embryos
- 90+ years of study … Drosophila Complete Genome sequence available
Drosophila does show very different embryonic development compared to vertebrates, but why is it still useful for wider studies of development?
- Many developmental genes in vetebrates were identified in Drosophila first. (E.g Hox genes)
- Demonstrates many general principles of development conserved across animals(e.g morphogen gradients, pattern formation)
- Experimentally very powerful hypothesis testing(e.g mutagenesis and transgenic; fully sequenced genome)
- Much more simple
