Developmental Genetics Flashcards
What type of polarities do most organisms show?
Dorsal Ventral and Apical Basal polarity
What type of symmetry does Arabidopsis show?
Radial Symmetry
What is the difference between intrinsic and extrinsic asymmetric cell division?
INTRINSIC = mother cell becomes polarized before division and forms two daughter cells with different fates EXTRINSIC = daughter cells are identical but cell signaling from surrounding cell or from precursor cell determine cells with different fates
Describe how a transient bias can lead to differentiation neighbor cells
A transient concentration bias of two cells producing the same factor can cause the production of the factor in one cell to increase and in the other to decrease (say the factor was an inhibitor to its own production).
A positive feedback system will create two fairly stable asymmetrical cells
What is a morphogen?
A morphogen is a signaling molecule that acts directly on cells to produce a specific response based on its local concentration
In what manner do the four functional groups of early development genes in drosophila interact?
In a hierarchal manner
What key genetic modification is used in mutant screens for drosophila development?
Female flies in the cross carry a balancer chromosome
What discovery was made that predicted there must be maternal factors acting in drosophila development?
After the discovery of the segment regulation that came from GAP and pair rule genes which was still occurring in the syncytium stage, there couldn’t have been more upstream zygotic genes which regulated this. Must have been egg contained determinants
What is the characteristic phenotype of a bicoid mutant
No head or thorax (anterior deletion)
What is the characteristic phenotype of a nanos mutant
No abdomen (posterior deletion)
In terms of bicoid and nanos, is there a polar prevelance in the action of these regulators?
there is anterior dominance over posterior
What factor does bicoid require to function as a transcriptional activator?
maternal hunchback
What feature of Bicoid homeodomain makes it rare?
The K50 homeodomain which can bind DNA and RNA (RNA binding via Arg54)
How does bicoid repress translation of caudal?
It binds to the Bicoid recognition element of the 3’ UTR of caudul mRNA recruiting a cap binding complex repressing translation
How was the morphogenic activity of bicoid discovered?
By specific polyclonal antibodies developed against the BICOID protein
Does hunchback effect gradient levels of bicoid?
No - maternal hunchback is present at uniform levels throughout the oocyte
How is the gradient of the transcription factor Dorsal initiated?
The gradient of nuclear localization is under the control of an extracellular signal.
It activates the Toll receptor which releases Dorsal from a cytoplasmic anchor
How does Bicoid bind the cap binding complex when repressing caudul mRNA
Bicoid has a short area of sequence homology with eIF4e - the binding motif for eIF4G, the cap binding scaffold.
How do the inversions in a balancer chromosome prevent it from recombining?
If crossovers occur between balancer and normal chromosomes - they will not segregate properly as they would either form acentric or dicentric products.
What is the general phenotype for mutants defective in maternal effects?
Large deletions of the body plan
What type of relationship do Hedgehog and Wingless show?
Positive reinforcement, one begets the other
Describe the heatshock experiments designed to understand interactions between homeotic genes
Heatshock promoters were added to Antp and Ubx genes in two strains of drosophila. This meant that when heatshock was applied, the genes were expressed throughout the whole genome.
In the Antp heatshock experiments, all parasegments anterior of PS4 took on the identity of PS4. Those posterior remained the same.
In the Ubx heatshock mutants, all parasegments anterior to PS6 took on PS6 identity and all those posterior remained the same. This means that there is posterior prevelance of the homeotic genes.
Discuss the antennapedia mutant phenotype
antennapedia is a mutant in Antp gene. Instead of replacement with SCR as is expected by posterior prevelance, grew legs where antenna should grow. This is because it was a dominant mutation - Antp is expressed ectopically in the head. Antp function is to block the development of antenna and leg is the default phenotype.
What is the purpose of the polycomb gene in Polycomb repressive complexes?
Polycomb and extra Sex Combs are components of the large multimeric complexes PRC1 and PRC2. These complexes target polycomb response elements - and recruit other DNA binding factors. Results in methylation of flanking histones = chromatin condensation. This silencing is stably inherited. Ensures homeotic genes are still correctly expressed when the GAP and pair rule genes are no longer expressed
What is the purpose of trithorax genes?
ensure some homeotic genes are still expressed after GAP and pair rule genes are switched off
What is the purpose of SMOOTHENED in the hedgehog signaling pathway?
SMOOTHENED inhibits the kinases which would phosphorylate Ci - meaning Ci can act as a transcriptional activator to Wingless genes
What is the purpose of PATCHED in the hedgehog signaling pathway?
PATCHED inhibits smoothened in the absence of Hedgehog - meaning Ci will be cleaved and will act as a repressor to Wingless genes.
What is the Ci orthologue found in limb development in vertebrates?
Gli3
What is the default state of digit formation?
polydactyly
How is digit identity decided?
The ratio of Gli3/Gli3R
Discuss the development of cyclopia in lambs
Some mothers graze on Californian corn lily - which contains the steroidal alkaloid cyclopamine. This binds to smoothened - inhibits Hedgehog signaling. Ventral induction does not occur
Discuss Gorlin Syndrome and its relevance to hedgehog signalling
Gorlin syndrome is a condition where a patient develops lots of basal cell carcinomas. PATCHED is mutated in the individual and defective. Hedgehog signaling pathway is constitutively active. (hedgehog singalling involved in hair follicle development)
what action would deactivating DISHEVELLED have on the wingless signaling pathway?
Deactivating disheveled would mean permanent activation of APC kinases. No functional signaling pathway
What is the orthologue of armadillo in humans?
B-catenin
What is the effect of wingless signaling in some colorectal cancer cases?
APC gene is often deleted - meaning no destabilization of b-catenin and constitutive activation of the wingless signaling pathway
What is the PRC1 homologue in humans?
BMI1
How many homeotic gene complexes exist in vertebrates?
There are four copies of the Hox complex in vertebrates (HOXA-HOXD)
What type of relationship do the A and C compartment of ABC model of plant development have?
Antagonising relationship
What is the innermost organ of a plant?
Carpel
What is the phenotype of apetala1 mutant?
No petals or sepals
What is the phenotype of a pistillata mutant?
No petals or stamen
What is an example of a signaling molecule through human embryo development?
Retinoic Acid (derived from Vitamin A)
What is the function of Retinoic Acid?
It acts as a ligand for nuclear RA receptors
What response does the binding of Retinoic acid to retinoic acid receptors have?
Switches them from transcriptional repressors to transcriptional activators
How is the level of retinoic acid controlled throughout embryonic cell populations?
There are differential pattern expressions of a small number of specific synthesizing and metabolizing enzymes throughout the cells which allow differential RA distribution throughout the cells
What is the maternal determinant for Retinoic Acid
Egg stored retinoids
