We have analysed the expression of keratins in the epidermis of normal human palm and sole skin (ridged skin) using immunohistochemistry and in situ hybridization. The epidermis of human ridged skin expresses a more complex pattern of keratins than thin skin, which is probably due to the greater stress that ridged skin has to withstand. In addition to keratin K9, we document specific expression patterns of keratins K6, K16 and K17 which are suggestive of regional adaptations of this epidermis to a high cell turnover rate. In particular, the sequestered location of nests of K17-positive cells at the bottom of the deep primary epidermal ridges supports the notion of functional heterogeneity of basal cells and suggests that the K17-positive sites may include stem cells. Expression of K6 and K16 in some basal and most suprabasal keratinocytes is compatible with a constitutively high proliferative activity of normal ridged epidermis, but may also reflect different physical properties of the suprabasal cells, in contrast with regions expressing K9. The distinct labelling patterns observed in primary and secondary epidermal ridges as well as epidermal layers above dermal papillae suggest the existence of local microenvironmental niches leading to differences in keratinocyte differentiation.
R .A . L I NC OL N AN D J . A. LE I GH . 1998. The binding of plasmin to Streptococcus uberis strain 0140 J was optimal in the pH range 5·0-5·5. Plasmin binding decreased exponentially with increasing NaCl concentration (0-0·8 mol l −1 ), reaching a minimum at NaCl concentrations exceeding 0·55 mol l −1 . Neither K ¦ , Mg 2¦ nor the metal chelator EDTA had any effect on the interaction. Plasmin binding was prevented, in a concentration-dependent manner, by the amino acids lysine, arginine and o-aminocaproic acid. Bound plasmin was also eluted from the bacterial cell using the same amino acids. Bound plasmin was lost from the bacterium in a time-and temperature-dependent fashion, the rate of plasmin loss increased with increasing temperature over the range 4-55°C, and the elution of plasmin from live and heat-killed bacteria was similar. Cell-bound plasmin was only partially inhibited by the physiological inhibitor a 2 -antiplasmin whereas the serine protease inhibitor aprotinin, and the active site titrant p-nitrophenyl-p-guanidiniobenzoate, inhibited the activity of the cell-bound plasmin by more than 95%.
abstract:We use Hubbell's neutral theory to predict the impact of habitat fragmentation on Amazonian tree communities. For forest fragments isolated for about two decades, we generate neutral predictions for local species extinction, changes in species composition within fragments, and increases in the probability that any two trees within a fragment are conspecific. We tested these predictions using fragment and intact forest data from the Biological Dynamics of Forest Fragments Project in central Amazonia. To simulate complete demographic isolation, we excluded immigrants-species absent from a fragment or intact forest plot in the initial census but present in its last census-from our tests. The neutral theory correctly predicted the rate of species extinction from different plots as a function of the diversity and mortality rate of trees in each plot. However, the rate of change in species composition was much faster than predicted in fragments, indicating that different tree species respond differently to environmental changes. This violates the key assumption of neutral theory. When immigrants were included in our calculations, they increased the disparity between predicted and observed changes in fragments. Overall, neutral theory accurately predicted the pace of local extinctions in fragments but consistently underestimated changes in species composition.
The gut microbiome provides access to otherwise unavailable metabolic and immune functions, likely affecting mammalian fitness and evolution. To investigate how this microbial ecosystem impacts evolutionary adaptation of humans to particular habitats, we explore the gut microbiome and metabolome of the BaAka rainforest hunter-gatherers 5 from Central Africa. The data demonstrate that the BaAka harbor a colonic ecosystem dominated by Prevotellaceae and other taxa likely related to an increased capacity to metabolize plant structural polysaccharides, phenolics, and lipids. A comparative analysis shows that the BaAka gut microbiome shares similar patterns with that of the Hadza, another hunter-gatherer population from Tanzania. Nevertheless, the BaAka harbor 10 significantly higher bacterial diversity and pathogen load compared to the Hadza, as well as other Western populations. We show that the traits unique to the BaAka microbiome and metabolome likely reflect adaptations to hunter-gatherer lifestyles and particular subsistence patterns. We hypothesize that the observed increase in microbial diversity and potential pathogenicity in the BaAka microbiome has been facilitated by 15 evolutionary adaptations in immunity genes, resulting in a more tolerant immune system. SignificanceHuman ecological adaptation requires changes at the genomic level. However, the gut microbiome, the collection of microbes inhabiting the gastrointestinal tract and their 20 functions, also responds significantly to ecological challenge. To determine how the gut microbiome responds to evolutionary adaptations in the host, we profiled gut bacterial communities of the BaAka, rainforest hunter-gatherers from Central Africa. The gut
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