lec 8- patterning the Drosophila embryo Flashcards
are all the axes in the Drosophila egg patterned?
yes
what does the AP axis give rise to when it is divided into regions?
the head, thorax, abdomen, and terminal
what are the 4 regions that the dorsal-ventral axis turns into?
-amniserosa (forms extraembryonic tissue)
-dorsal ectoderm (will form larval epidermis)
-ventral ectoderm (will form larval nervous system)
-mesoderm (will form muscles)
what do maternal factors do?
responsible for the patterning of the info, lay down the positional info and set up the AP axis and the dorsal-ventrical axis
what are maternal factors?
mRNA and proteins that are synthesized and deposited in the egg by the mother
what does the maternal factor do after development occurs?
-the maternal mRNAs are translated and the resulting proteins activate the expression of genes from the embryos own DNA in a specific spatial pattern along each axis
what causes the expression of zygotic genes?
maternal factors
what do zygotic genes do?
set the stage for the next round of spatial patterning
what are the types of zygotic genes and what do they do?
-the gap, pair-rule, and segmentation genes effectively divide the embryo into smaller and more distinct segments
-selector genes determine segment indentity
-gap genes divide embryo into hunchback (hb)
-pair-rule genes divide embryo into even skipped (eve) and fushi tarazu (ftz)
-segmentation genes divide the embryo into wingless (wg)
what is the maternal effect?
when the mothers genotype determines what the offsprings phenotype will be
if the mother is heterozygous for a mutant and the father is full mutant what will the phenotype results be?
(+/m x m/m = 50% +/m + m/m)
even though some are mutant, due to the mother having a wildtype allele, the children will all have normal phenotype
if the mother is fully mutant but the father is heterozygous, will the offspring’s all have a normal phenotype?
(m/m x +/m = 100% +/m)
no, they will all have mutant phenotype because the wild type allele does not come from the mother who controls the phenotype of the offspring)
what are the 3 types of mutations in maternal factors and what do they do?
-bicoid mutant: causes missing anterior structures
-torso mutant: causes both terminal regions to be missing
-nanos mutant: posterior is missing segments
which maternally provided mRNAs set up the anterior-posterior axis and where are they located?
-bicoid mRNA is tightly attached to the anterior position, nanos mRNA is tightly attached to the posterior position
-both of these are tightly attached but the proteins are not. After translation both of them diffuse away from the poles and form gradients of each protein along the anterior-posterior axis
-hunchback and caudal mRNA is evenly distributed
what is the bicoid maternal factors also considered?
a morphogen because it creates a gradient and sends a response
what is correlation?
when a factor is present during a role in the right place and time, but isn’t proven to have had an effect on the role
how do scientists know if a factor is necessary?
-by take away experiments, if being taken away stops the process, it is necessary
-if it being taken away does not stop the process, it is not necessary but it may still have a role due to redundancy
how do scientists know a factor is sufficient?
if it can perform the role by itself with no intervention from anything else, if it causes the effect in a place or time where it usually doesn’t occur
what are 3 forms of evidence to why bicoid is needed to pattern anterior structures?
- when the anterior side of embryo is being formed, bicoid is present, meaning it is correlated
- when an embryo lacks bicoid, it cannot form the anterior structures, indicating it is necessary for the formation
- when bicoid was added to a bicoid mutant, it cause the formation of anterior structures, making it sufficient
what is one type of posterior gene?
nanos
what happens if an egg is mutated in posterior genes?
it results in the larvae being short due to lack of abdomen
what acts as a repressor to stop hunchback mRNA from entering the posterior side of the embryo during fertilization?
nanos protein, it is crucial to stop the hunchback to have correct patterning
what acts as a repressor to stop caudal mRNA from entering the anterior side of the embryo during fertilization?
bicoid protein, high concentration near anterior low at posterior, vice versa for caudal
what types of proteins activate the anterior and posterior gap genes?
-bicoid proteins for anterior
-nanos and caudal proteins for posterior
what does the torso mRNA turn into after fertilization?
it is translated into torso proteins
what are torso proteins and where are they located?
they are receptors that are evenly distributed around the embryo
where are the ligands (a fragment of the protein Trunk) that attach to the torso receptors located?
only at the poles and once activated, zygotic genes are expressed
where is Trunk protein located and where is the protein that makes the ligands fragments located?
Trunk protein is present throughout the perivitelline space but the proteins that make the ligands are only found at the poles, very little ligand is produced, most of them bind to the torso receptors
