Developmental Biology Flashcards
Development
A change in structure of an organism over time
Regional specification
How a pattern appears in a previously similar population of cells e.g. body axes - anterior/posterior, ventral/dorsal and left/right
Morphogenesis
Shaping of organs and tissues in 3D that requires cell and tissue movements
Model organisms are studied to…
- Identify genes with roles in developmental processes
- Understand gene function
- Provide models for human disease
3 fates of stem cells?
- Self renew to generate new copies of themselves
- Differentiate into a somatic cell type
- Die by apoptosis
Mutations in the developing embryo can cause…
- Developmental defects
- Embryonic lethality
- Miscarriage
Mutation in PAX6
- Mutation in single copy of PAX6 causes Aniridia (loss of iris) in humans
- Mutation in both copies of PAX6 causes complete loss of eyes and fatal neurological defects
PAX6
- Codes for paired box class transcription factors
- Function is both necessary and sufficient for eye formation in the embryo
- PAX6 gene has been conserved from flies to mice to humans
Gametogenesis
- Gametes are derived from germ cells which form very early in embryogenesis
- Primordial germ cells give rise to cells that undergo meiosis to form haploid gametes
Haploid
Only one copy of each chromosome
Diploid
Two copies of each chromosome
Sperm structure
Male gamete
- Flagella to allow swimming
- Acrosomal vesicle contains enzymes for sperm to penetrate egg
- Lots of mitochondria to provide ATP for swimming
Oocyte structure
Female gamete
- Large stores of maternal RNA and proteins to support development during early cleavage stages
- Yolk which is a mixture of proteins and lipids
- Oocytes not fully matured, they are under hormonal control in ovaries
Fertilisation
- Binding of sperm to zona pellucida
- Acrosomal reaction as enzymes are released from sperm head
- Penetration of sperm through zona pellucida
- Fusion of plasma membranes
- Sperm nucleus enters egg cytoplasm to fuse with oocyte nucleus
Blocks preventing polyspermy
In sea urchin
- Change in membrane potential from -ve to +ve after sperm entry
- Cortical reaction results in formation of a fertilisation membrane and hyaline layer that blocks further sperms entering oocyte
Egg activation after fertilisation
- When sperm nuclei enters egg there is Calcium ion release
- Wave of Calcium across egg results in completion of meiosis, the pronuclei fuse and development begins
- Increase in calcium is both necessary and sufficient for egg activation
Cleavage
Rapid and synchronous division of cells with no overall growth to form ball of cells - blastula
3 patterns of cleavage?
- Holoblastic - humans
- Meroblastic - zebrafish
- Superficial - drosophila
Cell cycle in early embryo
- No G phase only S and M phases
Zygotic genome activation
- During cleavage zygotic genome is transcriptionally silent and embryo uses maternal supply of nucleotides and histones to replicate DNA content
- When these supplies run out, zygotic gene activation occurs and cell cycle slows and becomes asynchronous
2 mechanisms how cells differentiate
- Segregation of cytoplasmic content to become unequally divided between cells
- Cell-cell signalling using signalling molecules that lead to a change in gene expression
Mechanism of cell signalling
- Signalling molecule binds to receptor
- Intracellular transduction of signal
- Activation of transcription factor
- Expression of new genes
3 Germ layers and the structures they form?
- Ectoderm - skin, neural plate (neurones and glia), neural crest, placodes (inner ear, sensory ganglia)
- Mesoderm - muscles, heart, blood, bone, cartilage
- Endoderm - gut, pancreas, liver, lungs, pharynx, salivary glands
3 processes of gastrulation in sea urchin?
- Mesoderm cells send projections that attach to blastocele roof and pulls mesoderm and endoderm inside the embryo
- Forms a tube through the embryo - primitive gut
- Establishes the anteroposterior and dorsoventral axes§
Epithelium and Mesenchyme arrangement
- Epithelium - ordered
- Mesenchyme - random
Condensation tissue rearrangement
Cells that are spread apart become closely packed together
Mesenchymal to epithelial transition tissue rearrangement
Cells that are randomly assorted become ordered into epithelium
Epithelial to mesenchymal transition tissue rearrangement
Cells that are ordered break-off to become randomly assorted mesenchyme
Cavitation tissue rearrangement
Formation of an empty space surrounded by cells
Involution tissue rearrangement
Tissue sheet rolls inwards to form an underlying layer via bulk movement
Invagination tissue rearrangement
Epithelial sheet bends inwards to form an in-pocketing
Epiboly tissue rearrangement
A sheet of cells spreads by thinning
Convergent extension tissue rearrangement
Cells converge to intercalate between one another then extend in a perpendicular direction
Neurulation
Formation of the neural tube
- 2 neural plate borders move toward each other
- Invagination of neural plate forms the neural groove
- 2 neural folds converge to form neural tube
Spina bifida
Condition that results from failure of neural tube to completely seal
Neural crest cells
- Located above the neural tube
- Give rise to melanocytes, craniofacial bone/cartilage and neurones
Arrangement of 3 germ layers?
- Ectoderm - outer layer
- Mesoderm - middle layer
- Endoderm - inner layer
Drosophila
- Advantages
- Disadvantages
- Useful techniques
Advantages:
- Small organism
- Short generation time
- Large batch of embryos
- Sequenced genome
Disadvantages:
- Small embryo
Techniques:
- Mutagenesis
- Transgenesis
- Clonal analysis
Drosophila egg chamber
- Have axes when they are laid
- Have nurse cells - make RNA and proteins for developing embryo
- Nuclei migrate to edge of chamber to form a syncytial blastoderm
- Small number of nuclei migrate to posterior end to form pole cells which form the germ cells
Transplantation of pole plasm in Drosophila
- Cells from posterior end of one embryo transplanted into anterior end of a second embryo
- Cells retained pole cell functions
- Cells are transplanted back into posterior end of a third embryo
- Adult fly develops with germ cells with the same genotype as second embryo among its own germ cells
Imaginal discs of drosophila egg
Contain cells that have been set aside to form different body parts in the adult fly
What do mutations in the anterior of drosophila egg result in?
Bicoid mutant
2 types of genes that can effect development of drosophila egg?
- Maternal effect genes - determine polarity of the embryo e.g. bicoid genes in anterior of embryo
- Zygotic genes - responsible for body plan of the embryo e.g. gap genes, pair-rule genes, segmentation genes and selector genes
C. Elegans
- Advantages
- Disadvantages
- Useful techniques
Advantages: - Small organism - Invariant lineage - Short generation time - Sequenced genome Disadvantages: - Small embryo Techniques: - Mutagenesis - Cell ablation
If anchor cells are removed in C. elegans…
There is no formation of vulva
If anchor cells are mutated in C. elegans…
There is either no vulva or multivulva
