four times       estimated      declines     threshold

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four times       estimated      declines     threshold

Text C.

An annual, spatially structured matrix model predicts monarch population (1) __________ of 14% and a quasi-extinction probability of >5% below a viable (2) __________ within a century and compares simulations for overwintering habitat loss, extreme weather events, and loss of milkweed habitat. Monarch abundance was more than (3) __________ more sensitive to milkweed loss than to the other two hypothesized causes of declines. A Bayesian multivariate, auto-regressive, state-space model subsequently (4) __________ a more alarming quasi-extinction risk for the eastern population of North American monarch butterflies: 11–57% over 20 years. (Malcolm, S. B. (2018). Anthropogenic Impacts on Mortality and Population Viability of the Monarch Butterfly. Annual Review of Entomology, 63(1), 277–302. doi:10.1146/annurev-ento-020117-043241)

Exercise 7. Lexical cloze. Complete these sentences choosing the correct variant A, B, С or D.

Role for the longevity protein SIRT6 in primate development

Monkeys genetically engineered to lack the gene SIRT6 die a few hours after birth, displaying severe growth defects. This finding reveals a previously unknown role for the SIRT6 protein in primate development.

Shoshana Naiman & Haim Y. Cohen

For decades, biologists using model organisms such as mice and fruit flies have faced concerns about the relevance of their findings to humans. Using a model that is more evolutionarily similar to humans, such as another primate, could potentially (1) _____ this frustrating gap. In a paper online in Nature, Zhang et al. use CRISPR–Cas9 gene-editing techniques to generate macaque monkeys lacking the gene SIRT6. Strikingly, they show that the SIRT6 protein has a role in embryonic (2) _____ in macaques that was not previously uncovered in mice.

Mammalian SIRT6 removes acetyl groups from histone proteins. DNA is packaged around histones in the nucleus, and this deacetylation condenses the packaged DNA, (3) _____ gene expression. In mice, SIRT6 is known to be a longevity protein that regulates many factors that alter during (4) _____, including genome stability, (5) _____ and metabolism. Indeed, overexpression of SIRT6 in (6) _____ mice leads to health improvements and extends lifespan, (7) _____ SIRT6-deficient mice die a few weeks after birth, displaying features of premature ageing.

It is unknown whether SIRT6 is involved in longevity in humans. However, recent (8) _____ show that an inactivating (9) _____ in human SIRT6 causes overexpression of embryonic stem-cell genes, which leads to abnormal development and (10) _____ brain defects, resulting in embryonic death. These findings (11) _____ a previously unappreciated role for SIRT6 in embryonic development, which should be considered separately from its role in ageing.

Zhang and colleagues used CRISPR–Cas9 to create one male and three female macaque embryos that did not express SIRT6. The females died shortly after birth and the male died in the middle of gestation. The absence of SIRT6 caused severe, whole-body (12) _____ delays. Compared (13) _____ wild-type newborns, the (14) _____ showed lower bone density, lower levels of subcutaneous fat and immature intestines and skeletal muscle. The authors also found that SIRT6-deficient monkeys had smaller brains owing to delayed neuronal maturation and an increase in the (15) _____ of immature neural progenitor cells. Overall, the SIRT6-mutant animals were born much smaller than controls and showed gene-expression and morphological profiles closer to those of a typical three-month-old fetus than a full-term animal born after six months of gestation. (Abridged. From Nature 560, 559-560 (2018) AUGUST 22 2018 doi: 10.1038/d41586-018-05970-9)

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