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L19- defects of embryonic development
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- 1Potential impact of developmental biology on human health1. Understanding growth and differentiation can inform therapy of degenerative diseases.
2. Tissue engineering for transplantation using a patient's own stem or embryonic cells.
3. Decapulation of developmental events can occur in adult disease resulting in illness - 2Development- In human development, embryos develop in the womb, no new growth but increase in number of cells, resulting in blastocyst, which implants into the uterus of mother.
- 3Germ layersAt the end of gastrulation, 3 germ layers are present:
- Top layer: ectoderm; epidermus, NS
- Middle layer: Mesoderm; trunk skeleton, muscle, dermis, kidney, blood.
- Inner layer: endoderm; gut, liver, pancreas, lungs. - 4Susceptibility to developmental defects- susceptibility corresponds with organ development
- most organ development occurs at 3-8 weeks of development; organ systems and limbs develop during this time.
- Peak of risk of issue in embryonic development at 5 weeks. - 5Common defects- Cardiac and blood vessel defects are the most common: 1 in 115 births
EG: transposition of the great blood vessel (which can be resolved by arterial switch surgery)
Minor defects:
- Ankyloglossia: tongue tie
- Colombia of the iris
- cleft lip/palate
- polydactyly- extra fingers/toes - 6Causes of human embroyonic malformations- Unknown- 54%
- Genetic factors- 14% ie chromosomal aberrations such as duplicated/lacking chromosomes, or point mutations. EG downs syndrome
- Enviromental factors- 7%; drugs, chemicals, infections, maternal disease.
- multifactoral inheritance- 25%, inheritance of multiple genes with one or more enviromental factors - 7Example of defects caused by a single gene- Cleidocranial dysotosis, where clavicals are thinner or absent, resulting in hyperflexibility and dental abnormality.
This is caused by a defect in the RUNX2 gene involved in bone development - 8Example of developmental defects caused by environmental factors- Thalidomide- morning sickness drug launched before being properly tested. Resulted in children being born without limbs.
- Fetal alcohol syndrome- small head, behavioural issues, flat face
- Zika virus, transmitted via mosquito bites, results in undergrowth of the NS - 9Brain development in humans- brain development begins from the hollow neural tube, which form bulges and flextures that shape the brain
- the neural tube is derived from the ectodermal germ layer
How this happens:
1. between 17 and 23 days of development neurulation occurs;
2. midline of neural plate dips down and borders rise up, meeting in the middle, fusing to form the neural tube
- This involves a number of different genes, and if anything goes wrong defects in the neural tube appear (NTDs) - 10Neural tube defects: NTDs: Ectodermal defects- Which defect occurs depends on which end of the neural tube has been affected.
EG:
Defect at the top= anacephaly= no brain
Defect at the posterior= spina bifta; spinal cord exposed to the enviroment, risk of infection
- can be caused by genetic/enviromental factors; folate helps to prevent NTDs.
Less severe NTDs:
- hyphohidrotic ectodermal dysplasia; affects ectodermal organs- hair, sweat glands, teeth, and in females; mammary glands. Caused by a point mutation in ectodysplasin A gene, can be resolved by injecting Eda protein signalling factors (only been tested in mice). - 11Mesodermal NTDs- vertebral defects: mesoderm organised into somites, progenitors of vertebrae and axial muscles.
*Spondylocostal dysostosis is when this develops in a disorganised way
*Achrondroplasia; defect in cartliage cells, results in short stature and undeveloped bones - 12How digit duplications occurZHH: morphagen, sonic hedgehog.
- different digits formed from the mesoderm are formed by a gradient of ZHH
- ZHH is expressed in ZPA (zone of polarising activity) released from here and diffuses across limb bed.
High conc= pinky
Low conc= thumb
- If something goes wron within this gradient, digit duplications can occur. - 13Endodermal NTDs- endoderm gives rise to the gut, liver, pancreas and lungs.
Defects include:
- Lung aplasia- absence of lung
- Esophegeal atresia/fistula- extra tubes in the respiritoey sistem
- Omphalocele- bowel outside the body
Other gut issues:
- astresia aka 'double bubble'
- malrotation; rotation of the gut, strangulation of the gut- leading to ischemia - 14Neural crest- PNS is neural crest- derived
- Neural plate borders that fuse during neural tube formation give rise to migratory cell population; the neural crest.
- Neural crest cells are multipotent, and give rise to a number of of cell types.
- Form entire PNS inc sensory neurons , autonomic neurons , pigment cells, schwann cells and smooth muscle
- Adult neural crest stem cells can be identified in the skin, meaning there is a potential use for therapy.
Defects here include congenital aganglionic megacolon= Hirschsprung's disease
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- l19 defects of embryonic development
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- Rose P
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