Question

Describe in great detail the regulatory system that was used to express the eyeless gene in flies. Your answer must name the two components of this system, as well as a description of how they work together.

Answer 1

Biological overview:

It's possible to artificially direct eye morphogensis to any appendage of the body. Genetically engineered slieght of hand has been used to express the eyeless gene in various tissues throughout the body of the fly in order to clarify an understanding of development.

Directed gene expression in such experiments is carried out using EnchancerTrap GAL4 lines. GAL4 is a gene activator. It turns genes on and is easily manipulated using genetic engineering techniques to modify the original genome.A genetic vector carrying the yeast GAL4 gene is randomly ingerated into various sites along the genome. Some GAL4 vectors insert next to enchancers. These modified genomes and the animals that carry them are termed enchancer trap GAL4 lines. Different enchancer trap GAL4 lines express in different tissues depending on the activity of the enchancer into whoch the vector haas inserted.

Other lines have been genetically engineered by introduction of a vector carrying the eyeless gene. The gene is regulated by a promoter region, termed an upstream activating sequence(UAS), activated by GAL4. By placing the eyelesss gene under the regulations of GAL4, the gene can be activated wherever gene activator GAL4 is expressed. When these two lines are cross bred and the progeny examined, eyeless appered to be activated in the various tissues expressing the GAL4 transcription factor.

In this manner by targeting expression of the eyeless complementary DNA in various imaginal disc primordia, ectopic eye structures have been induced on Drosophila wings, legs,and antennae. The ectopic eye apper morphologically normal,consisting of groups of fully differentiated ommatidia with a complete set of photireceptor cells. These experimentes form the basis for considering eyeless to be the master control gene for eye morpholgenesis

The model for eyeless function suggests eyeless is required for the determination of cell fate inthe eye. The embyonic and larval expression patterns of ey are consistent with the early requirement of this gene: it is expreesed in the eye primordia in the embryo and before the morphogenetic furrow at time of photroreceptor determination in the thired instar larval. A subsequent study shows that the ey is not only required at earlier developmental stages for the initiation of photoreceptor development, but also in later stages when terminal photoreceptor - specific genes are expressed. A novel form of ey is expressed in the adult stage. It contains both the first and the seconds exons. Exons2 is in frame with exons 1 and its5 boundary is 15 base pairs in front of the first methionion reportes in the d1 transcript. Late ey expression begins in the late pupal stage and coincides with rhodopsin expression. The transition from the pattering in the eye disc to the expression of terminal photoreceptor - specific genes occurs during late pupal development.There is an initial decrease of expression in the first half of the pupal life, but ey transcripts starts to accumulate again starting at 2/3 of the way through pupal development

eyeless directly regulates rhodopsin1(rh) expression photoreceptor cells. rh1 is expressed specifically in photoreceptor cells R1 to R5. eyelesscells is expressed in bothlarvel and adult terminally differentiated photoreceptor cells. The homeodomine of Eyeless binds to the palindromic homeodomin binding site P3/RCS1 in the rh1 proximal promoter which is essential for rh1 expression. These results suggest that Pax-6/ey directly regulates rh1 gene expression by binding to the conserved P3RCS1 element in the promoter

Function of the two components:

Two- components signal transduction system enable bacteria to sense, respond, and adapt to a wide range of environments, stressors, and growth conditions. These pathways have been adapted to respond to a wide variety of stimuli, including nutrients, cellular redox stage, changes in osmolarity, quorum signals, antibiotics, temperature, chemoattractants, ph and more.The average number of two- components systerms in a bacteria genome.A few bacteria have none at all - typically endosymbionts and pathogens- and other contain over 200. All such system must be closely regulates to prevent cross - talk, which is rate in vivo.

In Escherichia coli, theosmoregulatory EnvZ/OmpR two- component system controls the differential expression of the outer membrane porin proteins OmpF andOmpC. The KdpD sensor kinase proteins regulates the kdpFABC operon resposible for potassium transport in bacteria includes E. coli and Clostridium acetobutylicum, The N- terminal domains of this protein forms part of the cytoplasmic region of the protein, which may be the sensor domain responsible for sensing turgor pressure.