Craniofacial Development Overview

• what sort of disturbances can occur in dental development?

  - number

  - size

  - shape of teeth

  - structure
• what are the 2 types of 'disturbed' dental development?

  - pre-natal (before birth)

  - post-natal (after birth)
• What is ectodermal dysplasia (ED)?


  Abnormal development of one or more structures of ectoderm

  - over 150 ectodermal dysplasia syndromes (1:1500 births)

  - most common= hypohidrotic ED.

  causes:

  sparse hair

  abnormal dentition

  absence of sweat glands, etc.

  characteristic facial features

  - can be X-linked, autosomal recessive or dominant
• What is cleidocranial dysplasia?

  This condition has an autosomal dominant mode of inheritance. Abnormality of membranous bone formation but cartilage also affected:

  - supernumerary teeth forming as a third dentition

  - continuous tooth formation unlocked

  - bone hypoplasia

  
  

  -> due to +/- of Runx2 ( a key regulator in osteoblast regulation & bone formation- it inhibits the formation of successional teeth)
• what are human teeth defined as?

  dyphodont = 2 dentitions, deciduous & permanent

  heterodont = diff. types of teeth

  thecodont = base of tooth completely enclosed in deep socket of bone
• what are neural crest cells?

  Cells that form from the neural plate that don't go into the neural tube or the overlying ectoderm during neurulation

  
• show the stages in human development

  
• why are zebrafish excellent research models?

  - fertilised & develop outside mother's body = ideal model organism for studying early development

  - similar genetic structure to humans (share 70% if genes wit us, 84% are known to be associated with human disease)

  - easier to house & care for than rodents

  - impact of any genetic mutation/drug treatment easy to see (they are transparent- changes can be seen using non-invasive imaging techniques)

  - lots of offspring

  - easier to introduce genetic changes (the embryos absorb chemicals added to their water easily)
• what have experiments in chicken which examine gene functions helped?

  helped elucidate underlying mechanisms of human genetic diseases & provide basis for testing novel therapies
• What makes the chick embryo 'an attractive model system'?

  - easy to access & observe

  - in early stages = human & chick embryo morphology v. similar → both amniotes & development v. similar

  - chicken & human genomes share considerable homology

  - molecular & cellular basis for many developmental processes & phenomena first described in chick, incl. limb patterning, neural crest migration, dorso-ventral neural tube patterning, bl. vessel formation, somite segmentation & left-right asymmetry

  - time lapse video microscopy can be used to image live chick embryos

  - classic 'cut + paste' experiments & mechanistic gene function-analyses can be done

  - combination of micromanipulations w/ gain or loss of function can be done

  
• what was haeckles embryo theory?

  Haeckel believed that, over the course of time, evolution added new stages to produce new life forms. Thus, embryonic development was actually a record of evolutionary history (ontogeny recapitulates phylogeny)

  
  

  - disapproved
• what is normal development?

  course of development for typical embryo, free of disturbances
• what is the aim of descriptive/comparative embryology?

  understand 'normal development
• what is epigenesis?

  organism develops in stepwise fashion from unorganised state
• what was the 18th century prevailing theory of how a zygote becomes and animal?

  preformation = idea that egg & sperm contains embryo - organism is preformed as complete miniature structure in sperm/egg

  
  

  -> the organism is performed as a complete miniature structure in the sperm or the egg and it simply grows larger as it develops

  
  

  -> 1st reproducing human would've had to have all succeeding generations w/in itself
• what are anatomical approaches in developmental biology?

  descriptive & comparative embryology
• what are the 3 approaches in developmental biology?

  - anatomical

  - experimental

  - genetic
• what is environmental integration in developmental biology?


  e.g. sex determination in crocodiles:

  temps experienced during embryonic development determine offspring sex
• what is evolution in developmental biology?

  changes in development → new body forms
• what is reproduction in developmental biology?

  egg+sperm → zygote → multicellular organism (egg+sperm)
• what is growth in developmental biology?

  control & co-ordination of cell division
• what is morphogenesis in developmental biology?

  aquisition (addition) of organised form

  zygote → distinct tissues & organs
• what is cell differentiation in developmental biology?

  zygote → 100s of diff. cell types
• what is the definition of ageing?

  process of getting older

  (from a fertilized egg (zygote), to a newborn, then adulthood)
• what is the definition of development?

  process of progressive change of organism