Lecture 6 - Conservation of mesoderm formation in vertebrates Flashcards
How does mesoderm induction show conservation in vertebrates?
nodal-related morphogens are involved in mesoderm induction in all vertebrates
How does gastrulation show conservation in vertebrates?
-mesoderm and endoderm are internalised by cell movements of gastrulation in all vertebrates
How does organiser function show conservation in vertebrates?
Dorsal mesodermal structures with homolgous functions present in all vertebrates e.g the node in mice
What is Brachyury?
- highly conserved gene present in all vertebrates
- T-box transcription factor expressed in mesodermal cells of the blastopore/primitive streak region and notochord
- involved in properties of the mesoderm (regulating developing of mesoderm in the posterior of all chordates)
What results from brachyury mutations?
- give similar phenotypes in different organisms (confirming functional conservation)
- inhibition results in failure of the notochord to develop and abnormalities in the posterior mesoderm (truncation of the posterior portion)
Give an example of highly conserved mechanisms in the molecular mechanism of organ development
Photoreceptor organs
- identified through moleulcar analysis of developing organ system s
- ancient evolutionary common origin
How do photoreceptor organs show an ancient evolutionary origin?
-homologues of the TF pax6 have key roles in the development of vertebrate and invertebrate eyes
Fruit fly (arthropod)
- pax6 homologue is eyelss
- eyeless mutant lacks eyes
- eyeless overexpression leads to the formation of ectopic eyes
Frog(chordate)
- Pax6 inhibition reduces eye formation
- Pax6 overexpression leads to the formation of ectopic eyes
Mouse
-small eye mutation corresponds to a mutation in Pax6 (homolog)
Human
-mutations in Pax6 give rise to aniridia (abnormality in the development of the iris)
What do the similarities in the muation phenotypes of Pax 6 homologues in Fruit flies, Frogs, Mice and Human reveal about our evolutionary history?
-the last common ancestor of all arthropods and chordates had a photoreceptor organ and Pax6 was a key regulator of its development
What similarities are there between Fruit flies and Vertebrate (e.g. frogs, humans, and mice) circulatory organs, and what does this tell us about our evolutionary history?
Fruit fly
-dorsal vessel acts like a pump and can be considered a heart-like organ
-the tinman gene codes for homeodomain transcription fact that is required for dorsal vessel formation
Vertebrates - the vertebrate homologues of tinman (nkx2.3 and nkx2.5) are expressed in the developing heart
Frogs
-inhibition of nkx2.3 or nkx2.5 blocks heart formation
-overexpression of nkx2.3 leads to larger heart marker expression
Human
-Mutations in the Csx gene (Nkx2.5) are associated with congenital heart defects
Mouse
-heart development is disrupted in Nkx2.5 knock out mice
-heart tube forms but does not loop and undergo normal morphogenesis
CONCLUSION
-the last common ancestor of flies and vertebrates had a circulatory pump organ and Nkx2.5/2.3 homolog was a regulator of its development
What are the two types of body symmetry in animal body plans?
Radial symmetry
-body parts are arranged like a spoke around a central axis
Bilateral symmetry
-left and right halves with mirror symmetry
-anterior to posterior axis and dorsal to vcentral axis
What are germ layers?
where tissues and organs develop from during development
What are the different germ layers in Diploblasts and Triploblasts?
Diploblasts(e.g. Cnidarians e.g. hydra)
-Ectoderm - covering of animal and the nervous system
-Endoderm - lining of gut and associated organs
Triploblasts (e.g. Molluscs, arthropods, chordates)
-Ectoderm - covering of animal and the nervous system
-Mesoderm - mucles, skeletal structures, circualtory system
-Endoderm - lining of gut and associated organs
What is gastrulation?
the process in which a gastrula develops from a blastula by the inward migration of cells
What are the differences in gastrulation between protosomes and deutrosomes?
Protosomes (Molluscs annelids and arthropods)
-“First mouth” - the blastopore opening gives ride to the mouth and anus
Deutrosomes (Echinoderms and chordates)
-“Second mouth” - The blastopore opening gives rise to the anus
-the mouth opening develops secondarily
What occured in the cambrian explosion?
- 543-495 mYA
- marked by a dramatic increase in the diversity of metazoans (animals) in the fossil record
- Large complex bilaterian forms are first apparent
- mineralised skeletons and shells of multicellular animal are first apparent
- the body plans of all modern animals are apparant in the cambrian fossil record
What fossil in the cambrian explosion is likely to be the ancestor of the somites and notochord?
The pikaia
-a primitive chordate from the mid-cambrian that shows evidence for somites and a notochord
What are the features of the chordate embryo body plan? (ancestral basal chordate)
- Notochord
- Hollow dorsal nerve tube
- Branchial arches (gills in fish, jaw bone,heart tissues and 3 inner ear bones in human) and phryngial slits
- repeating segmental somites
- post anal tail
What is a modern animal that shares several characteristics of the ancestral basal chordate?
Cephalochordates e.g. the lancelets
- anterior branchial arches
- repreated blocks of mesoderm
- notochord
- dorsal nerve tube
What influences the morpholgy of early vertebrate embryos?
Early embryos look very different
-mode of nutrition influences their morphology e.g. own food supply of taking nutrient from the mother
What patterns the mesoderm?
Nodal signalling
-because of the gradient of morphogen from the vegetal hemisphere
-strongest at the Dorsal blastopore lip (spemanns organiser) and weakest at the ventral side
-mesoderm arises around the equator of the embryo, in between the vegetal and animal hemispheres
-
What are the differences in the process of gastrulation in the amphibian and chicken development?
Amphibian
-Mesoderm moves inside the embryo through the blastopore
-gastrulation is first apparent with the formation of the dorsal blastopore lip (Spemann Organiser)
Chicken
-Mesoderm moves inside the embryo through the primitive streak
-Henson’s node is homolgous to thee dorsal blasto pore lip and has similar properties?
How can it be shown experimentally that Hensons node is homologous to the dorsal blastopore lip?
Can do a transplantation experiment
- take hensons node and implant it into the epiblast
- will induce formation of a second body axis
What has the ability to produce the second body axis?
the dorsal mesoderm (hensons node/spemanns organiser) which gives rise to the notochord
What is the dorsal mesoderm?
A region of the embryo where gastrulation is initiatied and where the mesoderm begins to move inside the embryo
What conserved features does the early development of amphioxus show?
- mesoderm forms around the equator of the embryo
- mesoderm moves inside the embryo through the blastopore
- mesoderm induction
What conservation is shown in mesoderm formation in vertebrates?
Mesoderm induction
-mesoderm induction specifies cells to form the mmesoderm
-nodal-related morphogens are involved in mesoderm induction in all vertebrates
Gastrulation
-mesoderm and endoderm are internatlised by cell movements of gastrulation in all vertebrates
Organiser function
-Dorsal mesodermal structures with homolgous functions present in all vertebrates e.g the node in mice
What is mesoderm induction?
Specifies cells to become the mesoderm
