part 1 Flashcards
Steps of Fertilisation?
1, Sperm binds to zona pellucida
2,Acrosomal reactions- release of acrosomal vesicle
3,Penetationtrhough the zone pellucida
4,fusion of plasma membranes
5, nuclei of sperm enters egg cytoplasm and fusion of nuclei
How does the egg prevent polyspermy?
- egg membrane potential changes from -70 to +20, sperm need a negative potential to bind to egg
- Cortical granules within egg fuse to membrane and excites , release content that forms the hyaline layer and fertilisation membrane
What is the role of Ca2+ in early embryogenesis?
- Ca2+ released upon sperm entry in egg, and activates complete meiosis
- it initiates the cleaving
What are the three types of cleaving?
- Holoblastic - whole cell divides
- Meroblastic- partial cell division, still share some cytoplasm
- Superficial - nulei divides only not cytoplasm
Describe two ways cells can become different in cell division?
- segregation of components to one side of the cell so when it divides one contains more or less of a certain cellular component
- cell signalling can cause the turning on and off of genes due to ligand receptor binding and transcription factors
What are the three germ layers?
mesoderm, ectoderm, endoderm
What derives from the ectoderm?
epidermis, nervous systen, facial skeleton, placodes, neural crest
What derives from the endoderm?
endoderm: gut, pancreas, liver, lungs, trachea, salivary glands, pharynx
What derives from the mesoderm?
mesoderm: muscle, cartilage, bone, kidney , heart, blood, dermis
What is the process of gastrulation?
Formation of the primitive gut. from the blastula ells, three concentric layers are formed by invagination starting at the blastopore. Establishes the anterior posterior axis and dorsal ventral
What is the archenteron?
gut cavity
Features of the epithelium cells?
highly ordered, tight junctions and high cell adhesion, often have cell polarity due to their content
Features of the mesenchymal cells?
loose, in contact with ECM, can migrate around
What is the condensation process?
When mesenchymal cells become epithelial, becoming more ordered and tightly packed.
What is epiboly?
the migration of epilelial sheets that thin and spread to elongate and eventually enclose. eg. the ectoderm in gastrulation
What is convergent extension?
is the process by which the tissue of an embryo is restructured to converge (narrow) along one axis and extend (elongate) along a perpendicular axis by cellular movement. It is a major contributor to the morphogenic movements that physically shape the vertebrate embryo
What is neurolation? and what are the key steps?
formation of the neural tube that then forms CNS.the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula.
- Neuroectodermal tissue differentiates from the ectoderm and thickens into the neural plate
- Neural plate bends and converges inside embryo
- Neural crest forms below ectoderms epidermis layer
- closure of neural plate forming the neural tube
- neural crest form PNS
- Somites form from the mesoderm long the tube
Where is the nervous system located in vertebrates and invertebrates?
invertebrates: ventral
vertebrate: dorsal
What is orthotropic transplantation?
Transplant form one embryo to another the tissue to the same place however you label the donor
What are the characteristics needed for a marker or label?
- visible at all stages of development
- doesn’t leak between cells, e.g. cannot pass tight junctions
- non toxic
- inherited by all progeny
What is the difference between specification and determination?
specification is reversible
Determination is irreversible
Difference between mosaic and regulative model of development?
Mosaic: cells determined early in development ( Roox 1888)
Regulative: not till later in development that cells become committed to a fate (driesch 1892) is non autonomous as cells don’t govern their own fate, the signals from surrounding cells and tissues do
very few models are mosaic most regulative due to changes in signals
what are 2 ways to test cell commitment?
culture in isolation
transplantation, move cells to a different are and see what they develop as, if they change fate. if it develops due to old position it was determined
What are morphogens?
A class of signalling molecules expressed from a local source. A concentration gradient forms and this specifies cell fates depending on where along gradient cell is
What is the french flag model?
a morphogen affects cell states based on concentration, these states are represented by the different colors of the French flag: high concentrations activate a “blue” gene, lower concentrations activate a “white” gene, with “red” serving as the default state in cells below the necessary concentration threshold.
Name ways a morphogen can be transported?
simple diffusion in extracellular space, transcytosis, ECM binds to it and moves it around
What is bicoid?
In drosophila it is a protein morphogen and also a transcrition factor to regulate the expression of the Hunchback gene.
Where is bicoid localised?
The anterior side of the drosophila egg
What does the Hunchback gene do?
Codes for a transcription factor to establish segmentation inf the body of the fly.
How does bicoid regulate Hb
have to have a certain concentration of biked to reach the threshold where Hb is then expressed
What are Gap genes?
genes that if not there see gap in the pattern of an embryo, code for transcription factors to turn on pair rule genes
What is induction?
signal from one cell to another to cause a change in specification of the responding tissue/cell
Name different stages that a gene can be regulated?
- mRNA transcription, RNA splicing, how RNA binds to ribosome, post translational modification, promoters and enhancers bind to either activation or repressors to control gene transcription
What is positive feedback?
The product of a reaction causes the reaction to start again, or it is the starting reactant
What are Somites?
Segmented blocks od undifferentiated mesoderm that receive signals to become muscle, dermis or bone
What does transcriptional activity depend on?
- external signals
- intrinsic signals
- Accessibility of the chromatin
- transcription factors
- set of binding sites on the gene
Name some muscle specific proteins?
myosin, tropomyosin, troponin
What is MyOD
a transcription factor, turns on pathway for the proteins that are specific to muscle in somites. I s not required for muscle cell differentiation as a second factor Myf5 works too but if both knocked out no muscle formation
Both genes positively feedback
What are satellite cells?
adult stem cells for muscle tissue, undifferentiated, but if muscle damage they proliferate
Name 3 ways gene expression can be visualised?
- in situ hybridisation - see where mRNA expressed in fixed specimen
- Antibody stain - see where protein expressed
- Transgenic lines - in live embryo, fluorescent proteins driven by cell type sciatic promoters
What are the 3 mesodermal progenitors in somites?
- Dermatomes - dermis
- Myotome - skeletal muscle
- Sclerotome - vertebre and ribs
List the 5 steps if muscle development from somites?
- Have uncommitted cells- mesodermal progenitor in somite
- Determination - receive external signals and upregualte MyOD
- Cells committed to adopt muscle fate, do not yet express muscle specific proteins though
- Differentiation - cells, stop dividing, align, fuse, express muscle specific proteins
- Maturation - arrangement of proteins into muscle fibres
