Total Internal Reflection Accounts for the Bright Color of the Saharan Silver Ant

The Saharan silver ant Cataglyphis bombycina is one of the terrestrial living organisms best adapted to tolerate high temperatures. It has recently been shown that the hairs covering the ant’s dorsal body part are responsible for its silvery appearance. The hairs have a triangular cross-section with two corrugated surfaces allowing a high optical reflection in the visible and near-infrared (NIR) range of the spectrum while maximizing heat emissivity in the mid-infrared (MIR). Those two effects account for remarkable thermoregulatory properties, enabling the ant to maintain a lower thermal steady state and to cope with the high temperature of its natural habitat. In this paper, we further investigate how geometrical optical and high reflection properties account for the bright silver color of C. bombycina. Using optical ray-tracing models and attenuated total reflection (ATR) experiments, we show that, for a large range of incidence angles, total internal reflection (TIR) conditions are satisfied on the basal face of each hair for light entering and exiting through its upper faces. The reflection properties of the hairs are further enhanced by the presence of the corrugated surface, giving them an almost total specular reflectance for most incidence angles. We also show that hairs provide an almost 10-fold increase in light reflection, and we confirm experimentally that they are responsible for a lower internal body temperature under incident sunlight. Overall, this study improves our understanding of the optical mechanisms responsible for the silver color of C. bombycina and the remarkable thermoregulatory properties of the hair coat covering the ant’s body.     

The SV40 TC-II(kappa B) enhanson binds ubiquitous and cell type specifically inducible nuclear proteins from lymphoid and non-lymphoid cell lines.

We have characterized the complexes resulting from the specific binding in vitro of proteins present in nuclear extracts of several lymphoid and non-lymphoid cell lines to the TC-I and TC-II sequences of the simian virus 40 (SV40) enhancer. No proteins could be detected, binding selectively to the TC-I sequence, but two proteins TC-IIA and TC-IIB were identified interacting specifically with both the TC-II/kappa B enhanson, 5'-GGAAAGTCCCC-3' (important for the activity of the SV40 enhancer in vivo), and with the related H-2Kb enhanson, 5'-TGGGGATTCCCCA-3'. The binding of these two proteins to mutated TC-II enhansons correlates with the effect of these mutations in vivo, suggesting that both proteins may be important for SV40 enhancer activity. The TC-IIA binding activity was present in nuclear extracts of mature lymphoid B cells and was increased in pre-B cell nuclear extracts by lipopolysaccharide (LPS) and cycloheximide treatment. Furthermore, complex formation between the TC-IIA protein and the TC-II enhanson was efficiently competed by the kappa B motif from the kappa chain enhancer, indicating that TC-IIA is the NF-kappa B factor or a closely related protein. However, in contrast to previous reports, a TC-IIA/NF-kappa B-like protein whose properties could not be distinguished from those of the TC-IIA protein present in lymphoid B cells, was found in nuclear extracts of several untreated non-lymphoid cell lines, notably of HeLa cells, but not of undifferentiated F9 embryonal carcinoma (EC) cells [F9(ND)]. The TC-IIA binding activity which was moderately increased in HeLa cell nuclear extracts by 12-O-tetradecanoylphorbol-13-acetate (TPA) and/or cycloheximide treatment could be induced in nuclear extracts of F9(ND) cells by cycloheximide, but not by TPA. Moreover, the TC-IIA binding activity could be induced in cytosolic fractions from F9(ND) cells by treatment with deoxycholate, indicating that these cells contain an inhibitor protein similar to the previously described NF-kappa B inhibitor, I kappa B. The second TC-II enhanson binding protein, TC-IIB, which could be clearly distinguished from the TC-IIA/NF-kappa B-like protein, by a number of differential properties, resembles the previously described KBF1/H2TF1 protein as it binds with a higher affinity to the H-2Kb enhanson than to the TC-II/kappa B enhanson, and its pattern of methylation interference on the H-2Kb and TC-II/kappa B enhansons is identical to that reported for the KBF1/H2TF1 protein.(ABSTRACT TRUNCATED AT 400 WORDS)     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Two Competing Habitus among Hong Kong Art Practitioners

This article offers a comparison of the status of the “traditional” medium of oil painting or acrylic in Hong Kong SAR and in Mainland China. This issue concerns the well-known discourse about the hand as medium; a typical example of what Pierre Bourdieu would call habitus. The representation of art as something produced by the hand has been the only habitus in Euro-America for a number of centuries, and it remains so among many participants of the social field of art. The development of this habitus followed very different paths in Mainland China and in Hong Kong, thanks to very different institutions in those places. Those responsible for their establishment in the 20th century, especially educational institutions, are analyzed and provide the backdrop for the analysis of the field of art in present-day Hong Kong. New institutions and new ways for these institutions to deal with art education are now changing the field of art in Hong Kong, creating new concepts to deal with the issue of forms of art seen as respectively “traditional” and “contemporary.” In ways very different than what happens in Europe, for instance, where even media that can be seen as “traditional” like oil painting tend to belong to a single “contemporary art” habitus, Hong Kong has seen the establishment of a state of competition between two habitus seen as unrelated. This article concludes with a brief portrait of the state of struggle between these two habitus within the Hong Kong art field.