Models and Principles in Animal Development (2 lectures) Flashcards
7 eukaryotic model organisms
Mouse, chicken, xenopus, zebrafish, drosophila, c. elegans, yeast
5 stages of vertebrate development
cleavage
blastula
gastrulation
neurulation
pharangula
cleavage stage
early cell division, but no increase in cytoplasmic mass
holoblastic cleavage
complete cleavage
meroblastic cleavage
incomplete cleavage, e.g. cells dividing only on one side
empty space in a cleaving embryo
blastocoel
blastula stage
hollow stage
gastrulation
germ layer formation, envagination of the mesoderm
neurulation
formation of the neural plate, folding of the neural tube
pharangula stage
post-anal tail, dorsal neural tube, segmentation- point at which vertebrate embryos tend to look very similar
hourglass model of development
period of morphological constraint- basic body structure being laid out w hox genes
xenopus pros and cons
pros
-easy to keep the adults
-external fertilisation, can get synchronised development of a bunch of embryos
-large embryos, easy to manipulate
cons
-slow to reach sexual maturity, annoying for genetics
-transgenics are difficult
zebrafish pros and cons
pros
-easy to keep, they’re fairly chill
external fertilisation for synchronised development
transparent, so good for microscopy
-short generation times- good for genetics
cons
-duplicated genome makes things hard sometimes
chicken pros and cons
pros
-eggs laid so easy to get to and manipulate
-windowing for easy access to the embryo
-good for grafting experiments
cons
-internal fertilisation, hard to access early stages
-embryos are dense
-long generation times, expensive to keep
unusual aspects of mouse development
inside of the gastrula ends up on the outside of the embryo- ‘flipped’ stage
embryo needs to ‘turn’ itself at 8ish days old
mice pros and cons
pros
-adults easy to keep in large numbers
-we know a lot about their genetics, so easy to do those kinds of experiments
-mammals, so more medically relevant
cons
-internal fertilisation and growth
-microscopy is a bit hard
summary- considerations when picking a model organism
can adults be kept in the lab easily?
embryonic size and accessibility
what techniques can be applied- e.g. injection, grafting, culture
genetics?
phylogenetic position
does it have the right character
cell fate
what a cell will, or has, become
cell lineage
where a cell came from
methods of tracking cell fate and lineage
photoconversion- activating a cell, and then following it
3D imaging- method of exactly tracing a lineage
commitment
when cells are on a developmental path
specification
reversible commitment
determination
irreversible commitment
differentiation
when specific functional cell types are formed (as inferred by morphology or transcriptional profiles)
how would we test if cells are committed?
looking at if the cells behave the same in culture as they do in vivo- e.g. do they make limb cells in culture
how can we tell if cells are specified or determined?
tranplantation- do cells fo what they do in the donor? this would make them determined
what did Mangold do
transplantation experiments on newts, showing that you can determine the functionality of specific regions early on in the embryo
what is an organiser region
region or group of cells which can both induce different fates of, and pattern, adjacent cells
what is pattern formation
the step generally preceding morphological change- distinct spatial territories are specified by different molecular or transcriptional identities
important model for determining positional identity
french flag model
what is a GRN
gene regulatory network- often quite complex set of gene interactions which help set up regions of a developing organism
key principles of the Turing reaction-differentiation model
-no external intervention
-patterns emerge at the global level from local interactions among smaller components
-idea of repression and activation systems- inhibitor which diffuses faster than the activator
-often get oscillatory patterns just from this inhibitor/activator pattern
turing vs french flag models
french flag model focuses on how positional information can be determined by local morphogen gradient- turing model says this info doesn’t directly correlate w morphogen conc
turing model is a bit less about direct determination of positional information based exclusively on morphogen concentrations