Embryology Flashcards
(20 cards)
What is gastrulation and neurulation?
Gastrulation is the process of epiblast cells migrating through the primitive streak to form mesoderm and endoderm; the epiblast left behind becomes ectoderm.
Neurulation is the process of some of those ectodermal cells (on the dorsal side of the embryo) folding up into a tube (the CNS), which then
becomes patterned by transcription factors
What is the process of neural crest development?
Neural crest cells undergo epithelial to mesenchymal transition (EMT) and migrate laterally and ventrally throughout the primary body axis, and in the head give rise to musculoskeletal tissues of the frontal face.
What are the 2 types of bone the head is formed from?
endochondral bone (cartilage that ossifies) and intermembranousbone (direct differentiation of
bone from mesenchyme). The viscerocranium and
chondrocranium (and the rest of the skeleton except the clavicle) are endochondral; the skull is intermembranous.
What drives differentiation in cranial sutures?
In cranial sutures, FGF signalling drives differentiation of mesenchyme into osteoblasts, forming bone. Different levels of FGF molecules (little purple dots) and different expression of receptors (FGFRs) control this. High levels of FGF signalling drive osteogenic differentiation. Carniosynostosis is generally associated with mutations of an FGF receptor or increasing FGF signalling.
What does the MSK develop from?
a combination of neural crest (cranially), chordamesoderm, paraxial mesoderm, and lateral plate mesoderm.
What is somitogenesis?
Happens at the wavefront. Once cells reach the determination front (ieonce the growing tailbud is far enough away from them that they cannot sense much FGF anymore), the undergo MET to produce somites.This depends upon the interaction of opposing RA and FGF/Wnt signalling
gradients. These gradients act upon a molecular
patterning system that gives the skeleton.
What is the patterning to ossification timeline?
What is the process of endochondral bone formation and growth?
What causes Pfeiffer syndrome?
mutation of FGFR1 or FGFR2
What characterizes Pfeiffer syndrome as a craniosynostosis?
Premature ossification at sutures
What does the mutation underlying achondroplasia cause?
Activation of FGFR3
What is intermediate mesoderm defined by?
‘Intermediate’ mesoderm is defined by Pax2 (another transcription factor) expression, and forms the urinary and internal genital apparatus
What are the 3 stages of kidney formation?
Pronephros, mesonephros, and metanephros. The former contributes to functioning kidneys in primitive jawless fish and persists in larval bony fish and amphibians, but it and the mesonephros
do not contribute to the mature kidney in mammals, which is comprised of the metanephros
What is the induction of ureteric bud outgrowth? (Metanephric organogenesis)
Glial-derived neurotrophic factor (GDNF) is secreted from the metanephric mesenchyme and induces bud outgrowth through binding to RET receptor: GDNF signalling is associated with promotion of cellular survival and growth and functions in all sorts of tissues (as an example, this figure is taken from a review on neuroprotective functions of GDNF signalling).
GDNF induces Wnt signallingfrom the buds. This promotes mesenchymal-epithelial transition of the mesenchyme (ie migrating cells) into epithelial cells (ie cells next to each other, forming a kidney tubule). When Wnt9b is knocked out (Wnt9b-/-, right), the kidneys simply do not form as the epithelialization does not occur.
What is hypoplasia and agenesis?
Hypoplasia is frequently symptomless and has been associated with mutations in genes encoding transcription factors involved in kidney development such as Pax2 and Eya1, which is regulates GDNF expression in the metanephric mesenchyme.
Agenesis is lethal, and leads to reduced amniotic fluid (oligohydramnios), which causes a Potter sequence: including a flat face, limb contractures, low-set ears, and dry, wrinkled skin. Neonates die following birth as a result of associated lung hypoplasia.
What are primordial germ cells?
PGCs are the cells that will form the ‘germ line’ ie the cells that will give rise to the gametes of the organism – the DNA that will be inherited by the next generation.PGCs migrate into the intermediate mesoderm from a population that is formed in the posterior end of embryo through the gut wall and into the genital ridges.
What are the gonads derived from?
The gonads are also derived from intermediate mesoderm, as are the ducts: the mesonephric duct (which becomes the ductus deferens, and degenerates in females) and the paramesonephric duct (which becomes the male oviduct, and degenerates in females).
Medially to the mesonephric ridge is the genital ridge, from which the gonads (testes or ovaries) are derived
How is primary sex determined?
The genital ridge is specified by expression
of transcription factors Wt1 and Sf1.𝛽-catenin expressionInhibits the expression of Sox9 and promotes the expression of Follistatin and
ovary-specific genes. Its activity and expression is reinforced by autocrine Wnt signalling.
Sry, the sex-determining gene on the Y chromosome, in collaboration with Sf1, initiates the expression of Sox9, which promotes testis-specific gene expression (in part through auto-regulation) and inhibits 𝛽-catenin.
What causes bilateral kidney agenesis?
Lack of mesenchymal to epithelial transition of ureteric bud mesenchyme
If a child is genetically a boy but has androgen insensitivity syndrome, what accompanies this syndrome?
Maintenance of the mesonephric duct
