The major histocompatibility complex-restricted antigen receptor on T cells: distribution on thymus and peripheral T cells

A monoclonal antibody, KJ16-133, which binds to antigen-specific, major histocompatibility complex-restricted (Ag/MHC) receptors on about 20% of BALB/c peripheral T cells has been used to examine the expression of these receptors on thymocytes and different subpopulations of peripheral T cells. Although KJ16-133-reactive receptors were found on mature thymocytes at similar frequencies and levels as on peripheral T cells, these molecules were absent from the first cells to enter the thymus, and in less mature thymocyte populations KJ16-133-reactive cells were less frequent than in the periphery and bore lower quantities of receptor. These results showed that Ag/MHC receptors are present on the surfaces of immature thymocytes, albeit at variable levels, during the time that the repertoire of these cells for Ag/MHC is thought to be selected. Additional experiments showed that KJ16-133 could not be used to distinguish T-cell receptors with different restriction specificities, i.e., for Class I or Class II products of the MHC.     

Stepparental Behavior as Mating Effort in Birds and Other Animals

In many animal species, widowed or divorced parents may remate before young of the prior union are independent. In such circumstances, stepparents may kill their predecessors' offspring, may tolerate them without providing care, or may invest in them more or less as genetic parents do. Rohwer proposed that all three of these responses may be understood as mating tactics, adapted to different social and ecological circumstances. We discuss the selection pressures that would favor each of these alternatives and review relevant evidence on nonhuman stepparenting, especially in birds. Stepparental tolerance and (partial or full) care, which are the predominant human responses, are common in nonhuman animals too, and in many cases there is evidence supporting their interpretation as stepparental mating effort adaptations. In general, however, this interpretation is not as well established for tolerance and care as it is for stepparental infanticide. Because tolerance and care are not distinct modes of behavior peculiar to stepparents, the hypothesis that they are nonadaptive by-products of parental psychology often remains tenable. We discuss the kinds of evidence needed to choose between by-product and stepparental adaptation hypotheses.     

Angiogenesis QTL on Mouse Chromosome 8 Colocalizes with Differential β-Defensin Expression

Identification of genetic factors that modify complex traits is often complicated by gene-environment interactions that contribute to the observed phenotype. In model systems, the phenotypic outcomes quantified are typically traits that maximize observed variance, which in turn, should maximize the detection of quantitative trait loci (QTL) in subsequent mapping studies. However, when the observed trait is dependent on multiple interacting factors, it can complicate genetic analysis, reducing the likelihood that the modifying mutation will ultimately be found. Alternatively, by focusing on intermediate phenotypes of a larger condition, we can reduce a model’s complexity, which will, in turn, limit the number of QTL that contribute to variance. We used a novel method to follow angiogenesis in mice that reduces environmental variance by measuring endothelial cell growth from culture of isolated skin biopsies that varies depending on the genetic source of the tissue. This method, in combination with a backcross breeding strategy, is intended to reduce genetic complexity and limit the phenotypic effects to fewer modifier loci. We determined that our approach was an efficient means to generate recombinant progeny and used this cohort to map a novel s.c. angiogenesis QTL to proximal mouse chromosome (Chr.) 8 with suggestive QTL on Chr. 2 and 7. Global mRNA expression analysis of samples from parental reference strains revealed β-defensins as potential candidate genes for future study.     

Evolution of altruistic cooperation among nascent multicellular organisms

Cooperation is a classic solution to hostile environments that limit individual survival. In extreme cases this may lead to the evolution of new types of biological individuals (e.g., eusocial super‐organisms). We examined the potential for interindividual cooperation to evolve via experimental evolution, challenging nascent multicellular “snowflake yeast” with an environment in which solitary multicellular clusters experienced low survival. In response, snowflake yeast evolved to form cooperative groups composed of thousands of multicellular clusters that typically survive selection. Group formation occurred through the creation of protein aggregates, only arising in strains with high (>2%) rates of cell death. Nonetheless, it was adaptive and repeatable, although ultimately evolutionarily unstable. Extracellular protein aggregates act as a common good, as they can be exploited by cheats that do not contribute to aggregate production. These results highlight the importance of group formation as a mechanism for surviving environmental stress, and underscore the remarkable ease with which even simple multicellular entities may evolve—and lose—novel social traits.     

Effect of clofentezine-hexythiazox resistance on life-table attributes of Tetranychus urticae Koch (Acari: Tetranychidae)

Life-table parameters of clofentezine-hexythiazox susceptible, resistant and back-crossed hybrid strains of Tetranychus urticae were studied to aid resistance management. Mean egg production (±s.e.) for the QRPH strain was 102.99 (13.452) and significantly more (P<0.05) than for strains S 67.18 (8.370) and S^QRPH 50.98 (6.180) which were not significantly different from each other. We consider the elevated level of egg production evident in the QRPH strain to be evidence of coadaption. The relative fitness of the resistant strain would make resistance management difficult.This work contributes in part for the fulfilment of the requirements of the degree of PhD at the University of Sydney.     

Effects of obesity and sex on the energetic cost and preferred speed of walking.

The metabolic energy cost of walking is determined, to a large degree, by body mass, but it is not clear how body composition and mass distribution influence this cost. We tested the hypothesis that walking would be most expensive for obese women compared with obese men and normal-weight women and men. Furthermore, we hypothesized that for all groups, preferred walking speed would correspond to the speed that minimized the gross energy cost per distance. We measured body composition, maximal oxygen consumption, and preferred walking speed of 39 (19 class II obese, 20 normal weight) women and men. We also measured oxygen consumption and carbon dioxide production while the subjects walked on a level treadmill at six speeds (0.50-1.75 m/s). Both obesity and sex affected the net metabolic rate (W/kg) of walking. Net metabolic rates of obese subjects were only approximately 10% greater (per kg) than for normal-weight subjects, and net metabolic rates for women were approximately 10% greater than for men. The increase in net metabolic rate at faster walking speeds was greatest in obese women compared with the other groups. Preferred walking speed was not different across groups (1.42 m/s) and was near the speed that minimized gross energy cost per distance. Surprisingly, mass distribution (thigh mass/body mass) was not related to net metabolic rate, but body composition (% fat) was (r2= 0.43). Detailed biomechanical studies of walking are needed to investigate whether obese individuals adopt novel energy saving mechanisms during walking.     

Transformation of Anaplasma phagocytophilum

Background  

Tick-borne pathogens cause emerging zoonoses, and include fastidious organisms such as Anaplasma phagocytophilum. Because of their obligate intracellular nature, methods for mutagenesis and transformation have not been available.     

Detrimental effects of reloading recovery on force, shortening velocity, and power of soleus muscles from hindlimb-unloaded rats

To better understand how atrophied muscles recover from prolonged nonweight-bearing, we studied soleus muscles (in vitro at optimal length) from female rats subjected to normal weight bearing (WB), 15 days of hindlimb unloading (HU), or 15 days HU followed by 9 days of weight bearing reloading (HU-R). HU reduced peak tetanic force (P(o)), increased maximal shortening velocity (V(max)), and lowered peak power/muscle volume. Nine days of reloading failed to improve P(o), while depressing V(max) and intrinsic power below WB levels. These functional changes appeared intracellular in origin as HU-induced reductions in soleus mass, fiber cross-sectional area, and physiological cross-sectional area were partially or completely restored by reloading. We calculated that HU-induced reductions in soleus fiber length were of sufficient magnitude to overextend sarcomeres onto the descending limb of their length-tension relationship upon the resumption of WB activity. In conclusion, the force, shortening velocity, and power deficits observed after 9 days of reloading are consistent with contraction-induced damage to the soleus. HU-induced reductions in fiber length indicate that sarcomere hyperextension upon the resumption of weight-bearing activity may be an important mechanism underlying this response.