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    One can create "knockout" mice that are missing a specific gene through a process called gene targeting. An investigator created such a mouse for a cell surface receptor expressed by the vast majority of B and T lymphocytes called Mel-14. After creating mice homozygous for this mutation (termed Mel-14-/-), she compared the number of B and T cells in the lymph nodes and spleen in wild type and Mel-14-/- mice. The data are summarized in the Table attached.

    Recall that lymphocytes recirculate between blood and lymph; and lymphocytes in each lymph node drain into the thoracic duct. To further characterize the Mel-14-/- phenotype, she performed a thoracic duct cannulation on groups of Mel-14-/- and wild type mice and collected and counted the number of thoracic duct lymphocytes (TDL) every 2 days over a 10 day period. Finally, after day 10, all cannulas were disassembled and the number of splenic lymphocytes in these mice determined. The data are summarized in Figures 1 and 2 (see file attached). Data from wild-type mice are shown in open bars; data from Mel-14-/- mice in closed bars.

    - What can you conclude from this experiment? What is the reasoning supporting this conclusion based off data?
    - What is a simple mechanistic hypothesis regarding the role of Mel-14 in lymphocyte trafficking that is consistent with these data?
    - What is one more experiment that would explore the validity of this proposed hypothesis. What would be the result you would expect if this hypothesis were correct?

    See attachment for graphs and data.

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    https://brainmass.com/biology/human-biology/mice-genetic-experiment-hypothesis-testing-364551

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    What can you conclude from this experiment? What is the reasoning supporting this conclusion based off data?

    You can conclude that MEL-14 is important for T cells, and possibly other cells, to enter lymph nodes. In the knockout mice, there are larger numbers of T cells in the spleen and less in the lymph nodes, suggesting the cells build up in the spleen as they cannot enter the lymph nodes. Data from the thoracic duct cannulation support this theory because there are many fewer cells exiting the lymph nodes, consistent with the idea that there are fewer T cells present.

    What is a simple mechanistic hypothesis regarding the role of Mel-14 in lymphocyte
    trafficking that is consistent with these data?

    One hypothesis is that MEL-14 is a molecule that is necessary for T cell to adhere to venules in the lymph node, enabling them to exit from the blood into the lymph node.

    What is one more experiment that would explore the validity of this proposed hypothesis. What would be the result you would expect if this hypothesis were correct?

    To test his hypothesis, sections of fresh lymph nodes could be made, then incubated together with either normal or MEL-14-/- T cells. These sections would then be washed, so that the only T cells remaining would be those that adhered to the venules on the lymph node section. Numbers of T cells would be counted on each section. If the hypothesis is correct, there would be fewer MEL-14-/- T cells on the sections than normal cells.

    This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!

    © BrainMass Inc. brainmass.com December 24, 2021, 9:18 pm ad1c9bdddf>
    https://brainmass.com/biology/human-biology/mice-genetic-experiment-hypothesis-testing-364551

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