Evolution of Development

Question 1

Evolutionary Aspects of Dev

Answer 1

• development stages look similar in vertebrates
• head is ahead of tail, eyes form early and brain chambers bulge out
• pharayngeal gill arches in all vertebrates of throat (part of jaw, inner ear or gills
• by beginning of neurulation all vertebrate embryos have converged on common structure despite starting development diff

Question 2

Evolution of Pharyngeal arch structures

Answer 2

• Pharyngeal arches in fish which in humans are part of inner ear
• For crocodile are for parts of jaw and skull
• Genes that are called Geography genes:
• Genes that differentiate head from tail and R from L - give direction and polarity to things

Question 3

Polarity Genes

Answer 3

• polarity genes establish anterior (head) and posterior ends - fruit fly
• geography genes - include polarity genes plus homeobox genes now thought of as the ‘tool kit’ genes
• Drosophila have geography genes despite not being deuterostomes
• Bicoid protein expresses at head end – bunch of nuclei and ones at front end know where they are and turn on the mRNA specific to bicoid protein which gets made at the head end
• mRNA translated into a bicoid protein and nice gradient seen where lots of bicoid protein at head and less as move toward back
• Hunchback RNA – whole first half of embryo expresses that gene

•Some genes only expressed at tail end and some region of fly w/both head and tail and others with just one side signal

Question 4

Body Plan

Polarity and Gap genes

Pair rule genes

Segment polarity

Answer 4

• Other genes signal segments throughout the body – all forms of geography genes
• Diff linear gradients
• Polarity genes establish head vs. tail (direction)
• Establish segments are called pair rules
• Segment polarity is whether segments face head or tail end
• *neural crest cells are not part of primary germ layers

Question 5

Enhancer Regions on Genes / Enhancer Region Modularity

Answer 5

•Next to genes there are enhancer regions – some enhancers turn up or down expression - enhancer regions can be cell type specific ex. Only turn on in skin for ex

• integration of longitude and latitude determines positions of small clusters of cells that will become limbs
• Gene that differentially expresses in dif cell types
• Gene A –in brain there are brain expressed TF that bind to and activate brain-specific enhancing to interact w/RNAPII to enhance transcription of that gene in the brain; and limb specific enhancer is not used but in limb its reversed
• Ex. Pax6 expressed in mice and various enhancers – retina enhancer, neural tube enhancer, lens and cornea enhancer – see embryo where red where gene is expressed to detect differential expression based on enhancers which makes diff part of embryo unique is controlled by enhancers

Question 6

Homeobox Genes (Hox Genes)

Answer 6

• Hox genes – homeobox genes
• Ex. Kind of fly generated in fly colony – 2 copies of thoracix segment #2
• 3 thoracic segment each has pair of legs; thorasic segment #2 has a wing that grows out of it and #3 has holtere (nobs) which is used for balance when flying
• No thoracic #3 just two sets of #2 so 2 sets of wings
• Found genes involved
• Antennapedia - when mutant fly has legs instead of antenna; segments of their bodies take on wrong identity - led to discovery of hox genes
• Hox genes - genes that control segment identity; humans have them too

Question 7

9 Hox genes in both flies and mice

Answer 7

• similar patterns of head to tail transcription of 9 hox genes in both flies and mice - these genes establish segment identity
• 9 genes that are hox genes – lined up in genome of fly in same order as expressed in embryo of mouse
• Cumulative effect where T1 has 2 genes expressing in same segment
• Diff combos of genes expressing in same region allows to take on appropriate identity
• Same genes in same order were present in all other animals including humans – genes are so similar that using recombinant DNA you can take human version and put it into a fly and it still makes a normal fly
• Ancient genes, establish through pattern of development and applies to all animals although in slightly diff way
• Mammals have multiple copies (4), flies have one copy

Question 8

Hox genes expression boundaries

Answer 8

• When genes express their effects they do it in certain region; in diff animals the expression boundaries of hox genes are shifted
• Hoxc6 – estab beginning of trunk of body and where 1st set of limbs come up
• In mouse if count down vertebrae and somites then see how far down hoxc6 gene it expresses, and it becomes trunk and limb bud; in chick, longer neck so hoxc6 express for trunk and first limb further down than mouse which gives chicks longer neck , goose even longer neck and has trunk determining gene even further down
• Python has no neck so expresses trunk gene almost right behind the head so no neck
• Hox genes determine region of the body in all diff animals

Question 9

Possible sources of stemp cells for therapeutic cloning

Answer 9

•Inner cell mass in developing embryo can be used for embryonic stem cells