考研英语阅读篇章: 寄生虫身体形变的关键因素
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Crafty(狡猾的) parasites frequently undergo dramatic shape changes during
their life cycles that enable them to adapt to different living conditions and
thrive. But these transformations might not be as difficult as they appear,
according to a study in The Journal of Cell Biology.
African "sleeping sickness" is a disease caused by a species of parasite
known as Trypanosoma brucei that is transmitted by the tsetse fly(采采蝇). The
single-celled parasite has a kinetoplast(动基体), which houses the cell's
mitochondrial DNA, and a protruding flagellum(鞭毛) that is crucial for cell
movement. T. brucei undergoes major changes in shape and form during its
developmental cycle. In one phase, known as the trypomastigote stage, the
kinetoplast is located posterior to the nucleus and almost all of the flagellum
is connected to the cell. In the epimastigote stage, on the other hand, the
kinetoplast is anterior to the nucleus, and only part of the flagellum is
fastened to the cell. T. brucei's close relatives come in many different shapes,
indicating that the parasites have also altered their morphology during
evolution.
When researchers from the University of Oxford reduced the expression of a
protein called ClpGM6 in T. brucei trypomastigotes, the cells switched to an
epimastigote-like morphology. The kinetoplast was close to the nucleus or
anterior to it, and a long section of the flagellum extended beyond the cell.
The parasites weren't identical to epimastigotes -- they lacked a distinctive
surface protein found at this life stage -- but they were able to survive and
reproduce for more than 40 generations.
ClpGM6 resides in the flagellar attachment zone and likely helps fasten the
flagellum to the cell body. Loss of ClpGM6 shortened the flagellar attachment
zone, which helps determine cell size and shape. The study suggests that
dramatic morphological changes during the life cycle and during parasite
evolution may result from adjustments in the levels of a few key proteins,
rather than from wholesale changes in the parasite's protein or DNA content.
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