Lecture 9 Flashcards
What are some characteristics of the PAX6 gene?
- contains 3 promoters and 3 txn initiation sites
- has more than 3 enhancers
- it is expressed at different times and in different organs during embryonal development
- it is expressed in certain parts of the brain in adult organisms
- PAX6 encodes a txl activator which regulates downstream genes
- tln of PAX6 mRNAs is regulated by several miRNAs
What is the PAX6 protein required for?
development of the eye, certain regions of the brain and spinal cord, and the pancrea cells
What regulates the expression of PAX6?
transcription control regions regulate expression of pax6 at different embryogenesis times in different tissues
*PAX6 has three alternative promoters that work in different tissues, the three promoters can produce three transcripts that will produce similar but not identical proteins
What is the PAX6 experiment on mouse embryo?
transgenic mouse expression of a β-galactosidase reporter transgene fused to different regions of Pax6 gene (stained with X-gal to reveal β-galactosidase)
*(b) Embryo 10.5 days after fertilization – 8 kb of mouse DNA upstream from exon 0 linked to reporter transgene
*Expression – in lens pit (LP) tissue that will develop into the eye lens and in tissue that will develop into the pancreas (P)
*(c) Embryo 13.5 days after fertilization – sequence between exons 4 and 5 linked to β-galactosidase reporter gene
*Expression – Retina and pancreas
*(d) Human PAX6 control regions:
*Several in the 600-kb region of human DNA between the upstream RCN1 gene and the downstream ELP4 gene promoter
*RCN1 and ELP4 are transcribed in the opposite direction from PAX6.
What is occuring before 10.5 days after fertilization in the mouse embryo?
the pax6 gene is inactive in all cells of the body (heterochromatin)
What is occuring 10.5 days after mouse embryo fertilization?
*pioneering txn factors open heterochromatin into euchromatin at the pax6 locus in the pancreas and the lens plate, all other regions, it remains in heterochromatin
*the pancreatic and lens/cornea enhancers activate PAX6, in all other organs, PAX6 remains in heterochromatin
*pancreatic and lens/cornea eenhancers will be occupied by multiple, but not identical txl activators (enhancosome)
*txl activators communicate with the GTFs, mediator, chromatin remodelling complexes and histone modification complexes
*histones are acetylated
*nucleosomes are displaced from the promoter region
*GTFs recruit pol II and txn begins
What occurs in the mouse embryo 10.5-13.5 days after fertilization?
*enhancosome exchange
*the lens/cornea enhancer stops working
*pancreatic enhancer cont.
*retina enhancer start operating, bend the DNA and come into proximity of the promoter
*miRNAs degrade PAX6 RNA and their function stops
*enhancosome exchange
What occurs in the mouse embryo after 13.5 days from fertilization?
talencephalon and rhomboencephalon will start working in the brain
What type of RNA regulates PAX6?
several types of miRNA (DICZER, RISC)
tissue specific miRNAs determine the stability of the PAX6 mRNA through binding to its 3’-UTR
What are the characteristics of the three transcripts that PAX6 can produce?
transcript a) is missing exon 1 and the alternative exon alpha
transcript b) is missing exon 0 and the alternative exon alpha
transcript c) is missing exons 1-4 but retains the alternative exon alpha (different function than b and a)
