Pattern Formation (Homeobox Genes) Flashcards
knockins vs transgenics
knockin: replace one version of a gene with another via ES cells (replace WT with specific mutation)
transgenics: add extra copies of any gene (injected DNA integrates randomly into genome and is transmitted to offspring)
homeotic mutations
what did discovery of these demonstrate?
mutation causing one structure to be replaced with another or duplicated
(ex: causing flies to have second set of wings, or legs growing where antennas should be)
demonstrated that there are genes which control patterning or generation of particular structures - these genes are homeobox genes
homeobox genes
encode transcription factors that initiate cascade of gene expression necessary for development of body structure or cell type
*mutations cause homeotic mutations
[~180bp in length, encode homeodomain protein domain, which binds the DNA in sequence-specific manner]
homeobox DNA encodes homeodomain protein TF, which recognizes and binds ___ rich binding site in promoters and enhancers
comprised of 3 alpha-helices
binds AT rich promoters and enhancers (TAAT)
homeodomain transcription factors form protein complexes in vivo to determine specificity
homeodomain is just one protein domain in homeobox transcription factor… what do the other proteins do
interact with non-homeodomain regions of transcription factor to form protein complexes that regulate DNA binding specificity and transcriptional activity
these genes function in patterning the body axis and are expressed in specific embryonic domain as to function in generation of that particular body part. What are?
Hox genes - positioned along chromosome in same order in which they are expressed along anterior-posterior axis
ortholog vs paralog
ortholog: homologous genes BETWEEN species
paralog: homologous genes WITHIN a species
explain conservation and expansion in gene number in evolution
common theme - conserved genes are expanded through evolution
example: Drosophila have 1 Hox cluster, while mice and humans have 4 (Hox 1-4 or a-d)
where are the Hox genes expressed (developmental structures)
neural tube and somites
explain spatial and temporal co-linearity in Hox expression
spatial co-linearity: Hox genes further 3’ have more anterior expression boundaries
temporal co-linearity: 3’ Hox genes are expressed earlier in development than 5’ Hox genes
Hox code
different groups of cells express distinct patterns of Hox genes depending on their position along the anterior-posterior axis
dictates the development of different structures along axis
LOF mutations (knockouts) of Hox genes lead to _____ transformations
GOF mutations (transgenic) of Hox genes leads to ____ transformations
explain this (best you can)
LOF —> anterior transformations (posterior region has anterior development)
GOF —> posterior transformation (anterior region has posterior development)
to explain, here is a story:
HoxA generates cervical vertebrae, HoxB is expressed more posteriorly and generate thoracic vertebrae
if HoxB is deleted, only HoxA will be expressed in posterior compartment, so there will be cervical vertebrae here instead of thoracic (*anterior transformation)
If the reverse deletion had occurred (HoxA deletion), this effect would have been reversed (thoracic vertebrae where cervical should be - *posterior transformation)
formation of head structures are controlled by homeobox transcription factor _____
Orthodenticle
Otd in Drosophila, Otx orthologs in mice and humans (functionally equivalent)
expressed in anterior brain regions
what would occur from an Otx knockout
anterior brain regions do not form during development
at top of transcriptional cascade - no other TF in genome can perform this function
is ectopic expression of Otd/Otx sufficient to generate neural tissue?
yes - it is at the top of the transcriptional cascade
this is sufficient to turn on the necessary genes in non-neural tissue
