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L3 - Morphogenesis (development of shape, i.e. development of single cell…
L3 - Morphogenesis (development of shape, i.e. development of single cell into multi-cellular organism)
- Be able to describe the basic process of building an embryo
- Be able to define the terms morphogenesis, morphogen, differentiation, determination
- Be able to define the body axes
- Be able to define maternal effect genes & describe their
influence on the phenotype of the embryo
- Be able to describe the effect of morphogen gradients on cell determination
- Know the role of the cytoskeleton and mRNA localization in development
Key Stages of Embryogenesis
- During this development, majority of somatic cells contain the same genetic material as the zygote
- Daughter cells differ from parent cells with respect to regulatory instructions and developmental fate
- Determination is the point at which cell has become comitted to a specific lineage and it's developmental fate is determined
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Homology
Homologous structures often arise
through homology at the gene level… same genes control development of arms in humans & wings in birds. 
E.g. PAX6 genes present across many species (deep homology) and the conserved sequences maintains the same function
Compound eye formation promoted in fruit fly with mouse Pax6 gene-
Developmental Decisions
- Most decisions in cell fate are binary and cocur during division
- Typically irreversible when commitment to lineage is determined
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Early Development in Embryogenesis
During fertilisation, when the ovum fuses with the sperm, the only cellular element contributed by the sperm is the Paternal Genome. The cytoplasmic contents of the early zygote, are almost exclusively contributed by the ovum. Thereby, those morphogens (RNAs and Proteins) which are initially present and which drive early development, originate from the genetic material contained within the ovum - i.e. products of the maternal genome
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Morphogens
Diffusable molecules (Intra & Extra - cellular) which determine phenotype according to their concentration-gradient and cell polarity
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Environmental Influences on Cell Fate
Prior to a cell's determination of lineage, it's developmental fate may be infleunced by environmental factors
Was destined to become square, but trasplanted prior to determination, and then responded to environmental stimuli which drove differentiation into hexagons
Cells are in a state of constant communication with the cells around them (Juxtacrine & paracrine) and their environment (extracellular matrix)
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