AMB15 Flashcards
(30 cards)
where does early drosophilia development take palce?
in a single cytoplasm consisting of many nuclei (syncitium)
proteins free to difuse and enter adjacent nuclei
where is bicoid translated
anterior end of syncitium
what does concentration of bicoid protein in syncitum show
highest where translated at anterior end of the embryo, decreasing as you move posteriorly.
exponential decay of expression indicating bicoid must be degraded as it diffuses posteriorly
what is bicoid responsible for the formation of
the head and thorax
what is bicoid
a homeobox domain TF for binding dna, directs expression of target genes. eg. hunchback which is not expressed in bicoid mutant
how do we know bicoid is a transcription factor
as it stimulates transcription in yeast of a constuct containing a hunchback 5’ site upstream of HIS3, without bicoid no histidine is made so yeast dies.
hunchback only expressed because of bicoid
what determines the posteror limits of expression
number and affinity of binding sites
increasing no. of binding sites in hb promoter or affinity extends posterior boundary.
- even if there is a small amount of bicoid there are more strong binding sites so expresion increases posteriorly
what do gene promoters need to activate a gene
a threshold amount of bicoid
what do sharp thresholds of gene expression boundaries come from?
cooperative binding at multiple sites, as one bicoid binds it encourages another to bind.
- quality of binding sites is not the same, some bind more or less tightly.
if there is twice as much bicoid how much more expression of hb would you get and why
more than twice as much due to cooperative binding
what affect will adding more bicoid have on fly phenotype
although posterior boundary will originally extend, regulation occurs later to stop it having a massive head and thorax.
what are embryos initially
a lose aggregate of cells called blastomeres
at what point do blastomeres compact together and form juctions
morula stage
when is the earlies sign of differentiation in mammalian embryo
during blastocyst stage where inner cell mass differentiates from trophectoderm ICM = more rounded, TD = flattened
what is a blastocyst
has icm which forms embryo and outer later of cells is trophoblast which surrounds icm and fluid filled cavity (blastocoele)
what does trophoblast give rise to
the placenta
what is a morula?
8 cell mass in spherical state
when are oct4 and nanog expressed
throughout embryo before late morula stage
where and when is cdx2 expressed
in outer layer of cells in late morula
what is cdx2 required for
repression of oct4 and nanog in trophectoderm around this stage.
what does oct4 represss
cdx2 in the icm so cant become trophectoderm
what does cdx2 repress
oct4 in trophectoderm
what does antognism between nanog and fata6 lead to
segregation of epiblast and primitive endoderm within inner cell mass
where is oct4 expressed
ICM
