Gastrulation and Neurulation Flashcards
What is gastrulation?
1- Process in early(ish) embryology
2- Bilaminar disc becomes trilaminar disc
What are the three layers of the trilaminar disc?
1- Endoderm
2- Mesoderm
3- Ectoderm
What is the notochord?
1- Structure in blastocyst 2- Lies along anteroposterior axis 3- Closer to dorsal than ventral 4- Induces neurulation 5- Later on forms spinal cord 6- Formed when epiblast cells burrow in between epiblast and hypoblast, forming notochord and mesoderm
How is the mesodorm formed?
Epiblast cells migrate through the primitive streak to form the mesoderm between epiblast and hypoblast
What is neurulation?
1- Folding of tri-laminar disc
2- Neural plate becomes neural tube
3- Induced by notochord
What induces the beginning of neurulation?
Notochord
What factors do the notochord and primitive node secrete at the beginning of neurulation?
1- Chordin
2- Noggin
3- Follistatin
Why do the notochord and primitive node release factors at the beginning of neurulation?
1- Block BMP effects (bone morphogenetic proteins)
2- Determine back and neural tissue development instead
Describe the formation of the neural tube.
1- Notochord induces neurulation
2- Ectoderm epithelial cells become columnar
3- Edges of neural plate thicken and migrate towards midline of embryo, fusing on the dorsal side to form a tube
4- Neural groove and neural fold become apparent
5- Folding begins at level of ~4th somite and continues cranially and caudally
When does the midline groove become apparent?
19+ days
When does closure at the cranial region of the neural plate occur?
~25 days
When does closure at the caudal region of the neural plate occur?
~28 days
What happens if cranial closure does not occur?
Anecephaly
What happens is caudal closure does not occur?
Spina bifida
What are neural crest cells?
1- Temporary group of cells
2- Arise from ectoderm
3- Produce a variety of cells e.g. melanocytes
4- Found at the border between neural tube and epidermis
What are examples of cells derived from neural crest cells?
1- Ganglia (cranial nerve, dorsal root, autonomic) 2- Adrenal medulla 3- Schwann cells 4- Peripheral glial cells 5- Smooth cardiac muscle 6- Odontoblasts 7- Thyroid parafollicular C cells 8- Melanocytes
What disorders can arise from defective neural crest development?
1- Pigment anomalies, may come with deafness and/or GI motility issues
2- Waardenburg’s syndrome
3- Treacher Collins syndrome
What is the cause of Waardenburg’s syndrome?
1- Defective neural crest development
2- Pax-3 gene deletion
3- SOX10 gene may be affected
What are the signs of Waardenburg’s syndrome?
1- Pigment abnormalities 2- Albinism 3- Deafness 4- Heterochromia 5- Telecanthus (wide-set eyes) 6- If SOX10 gene is affected, constipation
What is the cause of Treacher Collins syndrome?
1- Defective apoptosis of neural crest cells
2- Defective TCOF1 gene leading to defective Treacle protein
What are the signs of Treacher Collins syndrome?
1- Abnormal eye shape 2- Micrognathia (undersized jaw) 3- Conductive hearing loss 4- Underdeveloped zygomes 5- Malformed ears
What are somites?
1- Bilateral divisions
2- Along head-to-tail axis
How are somites formed?
1- Segmentation clock pathway
2- Wave of fibroblast growth factor FGF travels along head to tail end, creating somites
3- Cycle happens every 90 minutes
How often does the somite formation cycle go through?
Every 90 minutes
What are homebox genes?
1- ~160 bp long
2- Detemine body axes
3- Directly contributes to formation of body structures
What are the four topographical types of mesoderm?
1- Paraxial mesoderm
2- Intermediate mesoderm
3- Lateral plate mesoderm
4- Midline mesoderm (under neural tube)
What does the paraxial mesoderm derive into?
1- Head
2- Somite
What are the three layers/segments of the somite?
1- Sclerotome
2- Myotome
3- Dermatome
What does the intermediate mesoderm eventually give?
1- Kidney
2- Gonads
What are the two layers of the lateral plate mesoderm?
1- Splanchnic (cardiovascular system)
2- Somatic (body wall)
What are the two derivatives of the midline mesoderm?
1- Prechordal plate which forms
2- Notochord
What does the yolk sac become?
Gut tube
Where is the gut tube derived from?
Yolk sac
How is the gut cut off from the yolk sac?
1- Amniotic cavity
2- Enwraps the embryo, almost completely cutting off gut from yolk sac
What are the derivatives of the ectoderm?
1- Epidermis 2- Lens and retina 3- Olfactory epithelium 4- Oral cavity epithelium 5- Sensory organs of ear 6- Salivary gland 7- Sweat glands 8- Mammary gland 9- Adenohypophysis (anterior pituitary)
When is the vitelline duct obliterated?
~5-6 weeks
