lecture 15 Flashcards
is there a central controller for development
no; everything happens in individual cells
what is a domino
a signaling/developmental process in a specific tissue
what is the first domino to fall
fertilization of the egg
what is inevitable after first domino (fertilization of egg)
proliferation, differentiation thru expression of unique transcriptional regulators, all the way till adult organism
what happens as you transition from one stage of development to another
expression of specific transcriptional regulators
what happens when a transcriptional regulator is experssed
not just one protein that gets expressed, but ALL the genes that are controlled by that transcriptional regulator can be turned on/off leading to cell specialization
what are those transcriptional regulators controlling (what are some dominos)
promote/inhibit cell-cell interactions, promote/inhibit cell movement, proliferation thru pathways, up/downregulating actomyosin contractility to help w tissue morphogenesis
is there a master organizer of development
no. no CNS dictating what happens when, no master cell or central microchip
what’s controlling all these things in individual cells
every cell acts on its own in response to changes in transcriptional regulators expressed
give an example of every cell acting on its own rather than a central controller
steps leading to formation of an eye, instructions are contained in the cells that express first step of differentiation
what happens if u take cells that express initial precursor transcriptional regulator (that is gonna put cell and its progeny into developmental path to become an eye) and put it anywhere else on the embryo
its gonna become an eye (maybe not functional, but will still form)
why would it become an eye if we put precursor cell at a different location
b/c all the info you need (cascade of dominos gonna fall) for embryonic cells to become an eye are all in the cells itself
describe image B (eye like structure forming on diff parts where they shouldn’t be
dissected out embryonic eye cells and transplanted them to diff parts of cell –> they became eyes even at the wrong location cuz its just a series of dominoes that fall (same events are gonna happen in that new location, now you’re going to get an eye like structure there)
describe the system that controls development
highly conserved –> same processes in mice, humans, flies, equid, etc.
what is Pax6
transcriptional regulator, when expressed initiates a series of dominoes that have to fall over to convert pax6 expressing cell into a fully differentiated eye cell
what happens when they expressed pax6 from a squid in flies (where its not supposed to be expressed)
still does the same thing –> makes an insect eye (even tho its squid Pax6)
what does this show
common origins of multicellular life
what is initial fertilization event
single cell undergoes cleavage (goes from one cell to many cells) and forms blastula
what is blastula
hollow sphere surrounded by cells or blastomeres
what is initial stage where you get series of cleavage events
fertilized egg to blastula
what happens as u go from a single cell to bastula
proliferation but not growth; size does NOT change
what happens in gastrulation
blastula is turned inside out to form primordial gut (blastula to gastrula)
what can you notice in gastrulation
it is noticeably getting bigger, growth is happening, cell movement is happening
how do we know cell movement is happening
it has turned inside out
what else kicks into play as you go from blastula to gastrula
initial differentiation (you get 3 early cell fates, mesoderm, endoderm, ectoderm) AND morphogenesis (tube is formed)
what are 3 fates of cells that go to form many differentiated cell tyeps
ectoderm, endoderm, mesoderm
what is ectoderm
remains on outside of gastrulation embryo
what does ectoderm give rise to
skin and nervous system
what is endoderm
cells on inside of gastrulated embryo
what does endoderm give rise to
primitive gut & associated organs –> digestive system, esophagus, stomach, lungs, pancreas, liver, etc.
what are endoderm and ectoderm
looking to form epithelial like tissue where cells are forming cell-cell junctions and love being in contact w/ each other
what kinda tissue are endoderm and ectoderm similar to
epithelial tissue
what else is happening in ectoderm and endoderm
cadherins holding them together, belt of actomyosin contractility near apical surface
what is mesoderm give rise to
everything else: muscles, heart, blood, connective tissues (extracellular matrix rich tissues), kidneys
describe mesoderm; what is it similar to
more mesenchymal; like fibroblasts
how is mesoderm like fibroblast
forms single cells, doesn’t like forming cell-cell contacts w/ each other
can you tell sides apart in blastula
no; looks same, top, bottom, left, right
can you tell sides apart in gastrula
yeah; can tell top from bottom
how can you tell top from bottom in gastrula
opening to embryonic/primordial gut (at bottom)
can u tell left from right in gastrula
no; its symmetrical
what happens a few hours after gastrulation
profound asymmetry
what is symmetry breaking or axis specification
step going from symmetrical to us being to morphologically tell front from back, head from tail, left from right
when does symmetry breaking/axis specification occur
early development
why is axis specification a critical step
allows subsequent steps of development to follow more of a pattern, to reinforce & expand on this body plan specification that happens early
what is front
anteriorw
what is back
posterior
what is top
dorsal
what is bottom
ventral
when is basic body plan established
early in development
does basic body plan persist or go away
persists for lifetime of organism
what happens to ectoderm
ectoderm is still in outer portion of embryo which is where skin is going to form
what else do we now see in ectoderm
neural tube; going to become spinal cord and CNS
what is neural tube gonna become
spinal cord and central nervous system
what is mesoderm now
layer below ectoderm
what is mesoderm gonna become
connective tissue, musclesw
where is endoderm
in the middle
what is endoderm forming
gut cavity lined by endoderm
are these different cell types segregated? and when
segregated at early stage
what gives rise to tissue patterning
controlled differentiation in space and time (like EVE protein)
what is proper tissue patterning responsible
shape and function of adult organism
what happens once you specify body plan
can tell it left from right, front from back –> further steps of differentiation and morphogenesis
in early embryo are all cells are same or are they expressing diff things
look same but expressing different transcriptional regulators, going to have different face
what is blue part going to form
head
what is red (middle part) going to form
thorax
what is green (end) part gonna form
abdomen
are these relative positions at early stage maintained or not
maintained through adult stagew
why does body plan specification happen so early
b/c you need a framework to begin to place these different embryonic cells in correct locations, so adult tissues will form in the correct locations
what is tissue patterning
above process; body plan specification happening so early (, spatially regulated phenotypic trajectories are imposed on identical cells to generate distinct phenotypic cell domains.)
what does tissue patterning represeng
one of the dominoes that can fall during development
what can tissue patterning be a result of
several diff upstream cell signaling processes
what is largely responsible for differences between cell types
regulatory DNA
in tissue patterning, why do diff cells differentiate into diff fates
b/c they express diff transcriptional regulators
describe DNA as it goes from precursor cell/embryo to ultimate fate (muscle cell)
DNA isn’t changed
so how is there diff cell types
differentiated cells have different transcriptional regulators resulting in unique subset of proteins expressed in each cell types
so basically why are there different cell types
different proteins being expressed
why are there different proteins expressed
activation/repression of different transcriptional regulators
what does early embryo maintain into adulthood
body plan
what is changing in the different examples of tissue patterning we’re going through
changing which transcriptional regulators are expressed in different cells
what happens to the developmental potential of cells
becomes progressively restricted
what is general principle of development
as u go from early embryo/embryonic cell, at the early stage cell has many diff possibilities it can become
what can fertilized egg cell become
any cell type in the body
what is this fertilized egg cell fate called
totipotent
what happens as these dominoes fall
cell divides, generates diff cell fates; basically each step farther down the dev. path where u go from totipotent fertilized egg, to mesoderm endoderm ectoderm, to skin, heart, etc.
can you go backwards in developmental path
no; one way trip in terms of developmental fate
progressive restriction meaning
as cells differentiate to become more specialized, each step of differentiation there’s less and less things it can be
what do cells undergo
one way process of development from pluripotency to terminal differentiation