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Influence of Cell Polarization on the Shape of Fly Wings

This study investigates how cell polarization affects the shape of fly wings, specifically focusing on the role of the Narrow protein and Planar Cell Polarity (PCP) genes. By reducing the levels of PCP proteins in narrow-wing mutants, the researchers found that cell movement and wing elongation were affected. The results support the hypothesis that PCP-induced cell movements are necessary for achieving the correct shape of the wings. However, some unexpected outcomes were observed with certain PCP mutants, suggesting the need for further investigation.

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Influence of Cell Polarization on the Shape of Fly Wings

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  1. Does cell polarization influence the shape of fly wings? Gregory Campbell Central Catholic High School Pittsburgh

  2. The fruit fly, Drosophila • Used for over 100 years for genetic studies • Including studies in development - how you go from embryo to adult • Many mutants identified that disrupt development in different ways - used to identify the gene that is required for normal development • Provided insights into how all animals develop, including humans

  3. Wing from wild-type fly Wild-type Question: how do organs and appendages achieve their correct size and shape? ….why is the fly wing this shape? Mutants have been identified with wings with different shapes

  4. Wing from wild-type fly Wild-type In narrow (nw) mutants the wing is narrow narrow (nw) Goal: to understand why the narrow mutant wings are narrow…or..what does the wild-type Narrow protein do to make the wings the correct shape

  5. Nw wings are narrow because of too much cell movement during metamorphosis Increasing age This type of cell movement, when cells move in between each other, is known as Convergent Extension (CE)

  6. Frog embryos Increasing age CE also occurs in vertebrates embryos to make them elongate

  7. PCP genes control CE in vertebrates PCP = planar cell polarity PCP genes identified first in flies - control hair orientation Wild-type All hairs point towards the tip PCP mutant But not in PCP mutants

  8. Each cell is polarized PCP proteins are polarized at the edges of each cell - some on one side some on the other tip of wing Frizzled Prickle Van Gough Dishevelled Starry Night On both sides If you remove one protein none of the others is polarized

  9. PCP proteins are needed for CE cell movements in vertebrate embryos. Are they needed for the extra cell movement in narrow mutants? PCP induced cell movement Nw protein Hypothesis: the normal function of Narrow protein is to prevent too much CE cell movements ..so that in narrow mutants where there is no Nw protein, too much CE takes place and the wings become narrow ..so Nw protein inhibits the ability of PCP proteins to make cells move

  10. Experimental approach Reduce the level of PCP proteins in nw mutants to 50% (if you reduce it to 100% the flies usually die before they become adults) PCP induced cell movement Nw protein Expectation If the hypothesis is correct this should result in the wings becoming less narrow If we could knock out all Nw and all PCP the wings may look like wild-type

  11. Method • Cross nw mutant to different PCP mutants • Pick out nw/PCP flies • Pull wings off and mount on microscope slides • Take pictures • Measure length and width of 10 wings for each genotype • Compare l:w of nw/PCP to nw/+ • Use statistical test (t-test) to find if difference is likely to be real (p-value below 5%)

  12. Results Narrow mutant, no PCP mutant (nwD/+) Narrow mutant, prickle mutant (nwD pk/+ ) Some PCP mutants clearly make the nw wing less narrow

  13. Results 2.40 2.35 2.30 2.25 2.20 2.15 Length:width 2.10 2.05 2.00 1.95 1.90 1.85 prickle frizzled Van Gough Dishevelled Starry night No PCP mutant Wild-type no nw *p<0.05 Genotype (over nwD)

  14. What do these results mean? Frizzled Prickle Van Gough Dishevelled Starry Night On both sides Hypothesis: reducing PCP genes will result in wings becoming less narrow Results: Prickle, Frizzled and Dishevelled experiments support hypothesis Van Gough: does not support, unclear why? Starry night: has opposite effect than expected! It is not polarized to one side so this may produce this outcome although we don’t understand why.

  15. PCP induced cell movement Nw protein Conclusion • Reducing levels of some PCP proteins does prevent the wing elongating in narrow wings • Supports hypothesis that PCP-induced Convergent Extension cell movements are required to achieve the narrow wing • And so in wild-type wings, Narrow protein functions to prevent these movements making the wing its normal shape • However, it is unclear why reducing one PCP protein, Van Gough, does not produce the same result and why reducing another, Starry Night, has the opposite outcome.

  16. Future Knock down PCP protein levels more than 50% - more complicated genetic techniques (RNAi). Prediction - narrow wings will look even more like wild-type Investigate how PCP makes cells move: what does Nw protein do to stop CE cell movement. Biochemistry - find proteins that bind to Nw - test PCP proteins for binding to Nw?

  17. References • (1) http://www.sdbonline.org/fly/aimorph/wing.htm (Genes involved in tissue and organ development) • (2) http://flybase.org/reports/FBgn0002974.html (Gene report on narrow) • (3) http://fly.bio.indiana.edu/Browse/df/dftop.htm (Use to find Dfs at the Bloomington stock center) • (4) http://flybase.org/static_pages/cytosearch/ • cytosearch15.html (Use to work out which genes are present in a Df) • (5) Morgan, T.H., Bridges, C.B., Sturtevant, A.H. (1925). The genetics of Drosophila melanogaster. Biblphia Genet. 2: 262pp. (original report of narrow mutant) • Research done: • Dr. Gerard Campbell’s Lab • Department of Biological Science • University of Pittsburgh

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