Why do so many lymphocytes respond to major histocompatibility antigens?

A large fraction of T lymphocytes respond to allogeneic cells. Products of the major histocompatibility (H) complex influence the antigenicity of other cell surface components. We propose that lymphocytes responding to cells that differ genetically only at the major H locus recognize not only the major H difference, but also a multitude of other surface components in combination with the major H antigens. The large frequency of lymphocytes responding to allogeneic cells, then, becomes a function of the number of complex antigens they are recognizing on the foreign cells.     

Hunting, healing, and hxaro exchange: A long-term perspective on !Kung (Ju/''hoansi) large-game hunting

The question of why hunters target large game knowing that most of the meat will end up far beyond their own hearths is an intriguing one. It raises the issue of whether foragers pursue nonnutritional goals in food procurement and which goals they pursue. Here, I will use data from studies that have been carried out over a 34-year period among the Ju/'hoansi (!Kung Bushmen) to evaluate four hypotheses concerning why foragers target large game: reciprocity, costly signaling, nepotism, and long-term political goals aimed at bringing about conditions conducive to cooperative breeding. I will propose on the basis of qualitative and quantitative data that (1) all four hypotheses identify benefits that are gained by Ju/'hoansi through producing and distributing a surplus of meat, (2) different benefits might be important at different stages of a man's life, and (3) the pursuit of broader political goals merits serious consideration in accounting for men's work effort.     

Compliance, actuation, and work characteristics of the goat foreleg and hindleg during level, uphill, and downhill running.

We model the action of muscle-tendon system(s) about a given joint as a serial actuator and spring. By this technique, the experimental joint moment is imposed while the combined angular deflection of the actuator and spring are constrained to match the experimental joint angle throughout the stance duration. The same technique is applied to the radial leg (i.e., shoulder/hip-to-foot). The spring constant that minimizes total actuator work is considered optimal, and this minimum work is expressed as a fraction of total joint/radial leg work, yielding an actuation ratio (AR; 1 = pure actuation and 0 = pure compliance). To address work modulation, we determined the specific net work (SNW), the absolute value of net divided by total work. This ratio is unity when only positive or negative work is done and zero when equal energy is absorbed and returned. Our proximodistal predictions of joint function are supported during level and 15 degrees grade running. The greatest AR and SNW are found in the proximal leg joints (elbow and knee). The ankle joint is the principal spring of the hindleg and shows no significant change in SNW with grade, reflecting the true compliance of the common calcaneal tendon. The principal foreleg spring is the metacarpophalangeal joint. The observed pattern of proximal actuation and distal compliance, as well as the substantial SNW at proximal joints, minimal SNW at intermediate joints, and variable energy absorption at distal joints, may emerge as general principles in quadruped limb mechanics and help to inform the leg designs of highly capable running robots.     

Is Lake Prespa Jeopardizing the Ecosystem of Ancient Lake Ohrid?

Lake Prespa and Lake Ohrid, located in south-eastern Europe, are two lakes of extraordinary ecological value. Although the upstream Lake Prespa has no surface outflow, its waters reach the 160 m lower Lake Ohrid through underground hydraulic connections. Substantial conservation efforts concentrate on oligotrophic downstream Lake Ohrid, which is famous for its large number of endemic and relict species. In this paper, we present a system analytical approach to assess the role of the mesotrophic upstream Lake Prespa in the ongoing eutrophication of Lake Ohrid. Almost the entire outflow from Lake Prespa is found to flow into Lake Ohrid through karst channels. However, 65% of the transported phosphorus is retained within the aquifer. Thanks to this natural filter, Lake Prespa does not pose an immediate threat to Lake Ohrid. However, a potential future four-fold increase of the current phosphorus load from Lake Prespa would lead to a 20% increase (+0.9 mg P m⁻³) in the current phosphorus content of Lake Ohrid, which could jeopardize its fragile ecosystem. While being a potential future danger to Lake Ohrid, Lake Prespa itself is substantially endangered by water losses to irrigation, which have been shown to amplify its eutrophication.     

Taking the Scenic Route: Biosynthetic Traffic to the Plasma Membrane in Polarized Epithelial Cells

The maintenance of epithelial cell function requires the establishment and continuous renewal of differentiated apical and basolateral plasma membrane domains with distinct lipid and protein compositions. Newly synthesized proteins destined for either surface domain are processed along the biosynthetic pathway and segregated into distinct subsets of transport carriers emanating from the trans -Golgi network. Recent studies have illuminated additional complexities in the subsequent delivery of these proteins to the cell surface. In particular, multiple routes to the apical and basolateral cell surfaces have been uncovered, and many of these involve indirect passage through endocytic compartments. This review summarizes our current understanding of these routes and discusses open issues that remain to be clarified.     

Mutation induction by rodent liver microsomal metabolities of aflatoxins B1 and G1 in Neurospora crassa.

The mutagenic activities of aflatoxins B1 and G1 were studied in the ad-3 test system of Neurospora crassa by treatment of conidia with aflatoxin and liver homogenate for 2 h. No significant increase in the ad-3 mutation frequency over the spontaneous frequency was observed when either aflatoxin or mammalian liver homogenate was omitted from the test system. The ad-3 mutation frequencies increased to between 29 and 87/10(6) survivors, which is a 73- to 217-fold increase over the average spontaneous ad-3 mutation frequency (0.4/10(6) survivors), after conidia of N. crassa were treated with 0.67 mM aflatoxin B1, hamster liver homogenate, and a NADPH generating system. A 9- to 15-fold increase in the mutation frequency over the spontaneous mutation frequency was found when 0.67 mM of aflatoxin G1 instead of aflatoxin B1 was used in the test system. Treatment of conidia with 0.44 mM aflatoxin B1 mice liver homogenate and a NADPH generating system caused a small, but significant increase in the ad-3 mutation frequencies. No significant increase in the mutation frequency was found when a single sample of human liver homogenate was used in the test system. These studies show that metabolic activation is necessary for the expression of the mutagenic activity of aflatoxins B1 and G1 in N. crassa.