Development biology Flashcards
What is pattern formation/ regional specification in development?
The process by which a spatial and temporal pattern of cellular activities is organised within the embryo so that a well-ordered structure develops
An early step is allocation to different germ layers
What are the three germ layers?
Endoderm
Mesoderm
Ectoderm
What morphogenesis occurs in development?
Differential proliferation Change in cell shape and size Cell movement Cell fusion Cell death Gastrulation moves the germ layers relative to one another
Why is there little growth in early development?
Basic body plan is being established instead
The zygote is totipotent, what does this mean?
Generates all the cell types of the body and extra-embryonic tissues
What is differentiation?
Process of cells become structurally and functionally specialised, reflecting activation and maintenance of a particular pattern of gene expression
What is cleavage?
Rapid, multiple rounds of mitotic cell division where the overall size of the embryo doesn’t increase
The developing embryo is called a blastula after cleavage is completed
What does cleavage produce?
Cluster of blastomeres
What is the morula and when does it form?
Early stage in post-fertilisation development when cells have rapidly mitotically divided to produce a solid mass of cells (12-15 cells)
3 days after fertilisation
Post-morula, subsequential tangential cleavages produce one polarised and one non polarised daughter cell. Why?
Outer cells have distinct apical and basal surfaces
Non-polarised cells form inner cell mass
First differentiation event in mammalian embryonic development
What does the inner cell mass give rise to?
The embryo proper, and some extra-embryonic structures
What is the blastocoel?
Fluid-filled blastocyst cavity
What does active transport of sodium ions lead to in the blastocoel?
Active transport of sodium ions leads to fluid accumulation in the blastocoel
As ion conc increases, water flows in by osmosis
This inflates blastocoel
What is the trophectoderm?
Outer cell layer of blastocyst that develops as well as inner cell mass
What is the trophoblast derived from?
Trophectoderm
What does implantation require?
Interactions between trophoblast cells and uterine cells
What do the trophoblast cells do to help with implantation?
Express integrin proteins, which interact with extracellular matrix proteins expressed by epithelial cells of the uterine mucosa
Integrin/ laminin interactions promote attachment
Integrin/ fibronectin interactions promote migration
At implantation, what is the inner cell mass now called?
Embryoblast
What does the embryoblast form?
Epiblast
Hypoblast
What is the epiblast?
Columnar cells adjacent to newly formed amniotic cavity
Will form embryo proper
What is the hypoblast?
Small cuboidal cells adjacent to the blastocyst cavity
Will form extra-embryonic structures that will connect to the mother’s circulation
Where does the primitive streak form after 2 weeks and what is it?
Forms on surface of epiblast in the region that will become posterior of the embryo
First sign of anteroposterior axis
What happens in gastrulation?
Gatrula forms from blastula
Epiblast cells migrate through the primitive streak to create 3 germ layers
What happens during neurulation?
Ectoderm folds along its central axis to form the neural tube
What does the paraxial mesoderm segment into and what do these generate?
Somites
generate trunk and limb muscles, dermis and vertebrae
What does the endoderm give rise to?
Epithelial lining of gastrointestinal tract
What happens during the embryonic period?
Germ layers give rise to tissues and organ systems (organogenesis)
This is where most structural birth defects are induced
What are the common stages most animals develop through?
Fertilisation Cleavage to form blastula Gastrulation to reorganise structure and generate germ layers Neurulation Organogenesis
What are differentiated cells characterised by?
The proteins they contain
What is genomic equivalence?
Almost all somatic cells have a complete copy of the genome
What does VegT do?
VegT is a protein that binds DNA and actives expression of transcription factors that mediate endoderm differentiation and nodal TGFbeta signalling factors that are secreted and induce responding cells to form mesoderm
How is development affected by blocking VegT gene function?
Removing VegT from the oocyte interferes with both endoderm development and mesoderm induction
