lecture 27 Flashcards
What does the development of an organism require?
- regulation of organ size/growth
By what are developmental programmes dictated?
- a cell’s history (intrinsic mechanisms)
- (extrinsic mechanisms) interactions with the cellular environment including cell-cell interactions and hormones
How have drosophila been a useful tool?
Useful to find genes involved in development, but in particular genes involved in cell growth or cell death
How did advanced Drosophila genetics create a novel screen design for growth control genes?
- drosophila FRT-mediated mitotic recombination
- 3 types of tissue: wildtype, heterozygous, mutant
- heterozygotic mutant/+ parent cell
- low level heat shock with hs-FLPase
- exchange in small % of cells
- mitosis
- homozygotic daughter cells
- site specific recombination events
- basically a way of generating embryos that have all three types of tissue
- mosaics
- mutant tissue in the context of wildtype tissue
What are ‘loser’ cells?
- genetic mutations cause cells to grow slowly i.e. ‘loser’ cells
- in adult tissues you never see mutant clones –> losers
- higher fitness, less fitness
What will mutations in genes that restrict cell growth allow?
- over-representation of mutant tissue
- induce clones during mitosis using FLP/FRT system in the eye-antennal disc that result in mutant cells that outcompete loser cells
- insightful screen
What did the FLP/FRT ‘loser’ genetic screen identify?
- identified genes that regulate organ size
- Hpo pathway
- genes that were required to repress or negatively regulate cell growth
What is the SWH growth pathway?
- identified by the screen
- Salvador/Warts/Hpo
- salvador: mutants had larger eyes, also other tissues e.g. notum, wing, leg
- hpo: clones overgrow, head capsule, eyes, nodum
- these genes are conserved in mammals: Hpo = Mst1/Mst2 (2 hpo genes in mice/mammals)
- discovery of pathway that regulates organ growth in drosophila but also mammals, zebra fish, mice etc (and humans)
How does the SWH pathway regulate organ size?
- via inhibiting normal patterns of cell death
- increased number of inter-ommitidia cells in mutants, disrupting patterns of the eye
- loss-of-function clones of SWH pathway genes inhibit cell death by increasing dIAP1 expression
- loss of function clones of SWH pathway genes increase cell proliferation by increasing cycE expression
- two things happening in mutant cells:
- inhibition of cell death
- upregulation of cell proliferation
What do the core components of the SWH pathway form?
- a kinase cascade
- Hpo and Salvador (Sav) physically interact
- Warts (Wts) and Mob as tumour suppressor (Mats) physically interact
What kind of protein is Hpo?
- serine threonine kinase
- binds salvador
What kind of protein is Wts?
- kinase
What are key regulatory mechanisms of controlling this pathway?
- phosphorylated Wts
- phosphorylated Hpo
What is Yki?
- Wts phosphorylates co transcription activator Yki and excludes Yki from the nucleus
- phosphorylation of Yki creates a binding site niche for 14-3-3 proteins to bind
- these proteins exclude Yki from the nucleus
- unphosphorylated Yki enters the nucleus and activates target gene expression e.g. cycE, dIAP1
- Yki is a co-transcriptional activate
- binds Sd which is the DNA binding protein
- so the whole idea of the pathway is to maintain Wts in a phosphorylated state so that it can donate a phosphate group to Yki
- this phosphorylated Yki is excluded from nucleus from binding 14-3-3 protein, remains in the cytoplasm
- when the pathway is inactivated –> Yki enters nucleus –> activates genes involved in cell growth (e.g. cycE) or downregulates apoptosis (dIAP1)
What is apico-basal cell polarity?
gives cells a top and bottom
cells are highly structured
joined together through adherens junctions (in drosophila through septate junctions)
- all proteins involved in regulating wts are in the apical part of the cell
