Organogenesis Flashcards
Gastrulation at day 18
Neural plate is formed
- consists of tall columnar cells (becomes the epidermis)
Gastrulation at day 25
Primitive streak disappears
What happens during the 4th week?
The germ disc is transformed into something that looks more like a body
- embryo folds into a 3D structure which initiates the formation of organs
When does organogenesis take place?
4th-8th week
After 8 weeks it is considered a fetus
Anencephaly
Caused by the failure of the anterior neuropore to close. This is always fatal
Craniorachischisis
Failure of the entire neural tube to close. Fatal
Spina Bifida
Caused by failure of the posterior neuropore to close. Can cause paralysis or less serious issues
What type of factors are secreted by the cells of the organizer to assure that dorsal ectodermal cells assume a neural rather than an epidermal fate?
BMP inhibitors
What are the three major domains that are formed from the ectoderm
the surface ectoderm (primarily epidermis)
the neural crest (peripheral neurons, pigment, facial cartilage)
the neural tube (brain and spinal cord)
Neural Plate
Portion of the ectoderm that forms the brain and the spinal cord
Neurulation
Process of forming the neural tube from the neural plate
Primary Neurulation
When the neural tube is formed by invagination and pinching off (epithelial). Head to tail direction so the anterior neuropore closes first and the posterior one closes last
Secondary Neurulation
When the neural tube is formed by coalescence of mesenchymal cells to form a rod followed by cavitation to in order to form a tube. Only occurs at the posterior end of the animal
Junctional Neurulation
The transition zone between primary and secondary neurulation. Both primary and secondary are occurring in the same piece
Medial Hinge Point (MHP)
Anchored to to notochord (allows lateral cells to rise)
Dorsolateral Hinge Points (DHLP)
Anchored to the surface of the ectoderm
Become wedge shaped to drive the curling into a tube
make the neural tube converge medially
When does the neural tube close in humans?
Around day 28
How many major sites are there for neural tube closure in humans?
5
Folic Acid
A water soluble B vitamin
necessary for neural tube closure but they are unsure why
Where are motor neurons formed?
They are formed where Pax6 (inhibited by Shh) and Nkx6.1 (activated by Shh) expression overlaps, midway through Shh expression in the neural tube.
How does high BMP activity end up above the neural tube?
pinching off of the midline dorsally
this is also where the phosphorylated SMAD1 is
How is dorsal-ventral polarity established in the neural tube?
The inductive interactions with the notochord and the epidermis
The ventral neural tube develops…
Motor neurons
The dorsal neural tube develops…
Sensory neurons
What morphogen does the notochord use to induce the floor plate?
Shh
What morphogen does the notochord use to induce the roof plate?
BMP
What do rhombomeres form?
Nerves and ganglia (rhombomere 1 forms the cerebellum)
How are rhombomeres and hox genes related?
They follow the same rules, if hox2 were knocked out then rhombomere 1 would get expressed more posteriorly as well. Also posterior prevalence rule stands
