Inductive activity and enduring cellular constitution of a supernumerary apical ectodermal ridge grafted to the limb bud of the chick embryo.

Apical ectodermal ridges (AERs) isolated from 3- to 4-day chick and quail embryos were prepared by means of trypsinization and microdissection and then were grafted to the dorsal or ventral side of a host chick wing bud. They induced supernumerary limb outgrowths from the host bud showing, respectively, a bidorsal or biventral organization, as determined by the patterns of feather germs. The grafted ridge cells persisted, as revealed by histological sections of supernumerary chick limb parts growing under the influence of quail AERs, whose cells are readily distinguished after application of the Feulgen reagent.These results show that the AER induces limb outgrowth regardless of whether it is associated with dorsal or ventral limb ectoderm and that its continued existence is not dependent on contributions of ectodermal cells from the opposed ectodermal faces of the limb bud. The AER is pictured as maintaining the subjacent mesoderm in a condition of developmental plasticity without specifying its differentiation with respect to the proximodistal axis. It remains uncertain whether the positional values of cells that develop under the influence of the AER arise within these cells themselves or appear in response to influences from proximal sources.     

Strategic analysis in evolutionary genetics and the theory of games

This paper is written in memory of John Maynard Smith. In a brief survey it discusses essential aspects of how game theory in biology relates to its counterpart in economics, the major transition in game theory initiated by Maynard Smith, the discrepancies between genetic and phenotypic models in evolutionary biology, and a balanced way of reconciling these models. In addition, the paper discusses modern problems in understanding games at the genetic level using the examples of conflict between endosymbionts and their hosts, and the molecular interactions between parasites and the mammalian immune system.     

Immunologic and clinical improvement of progressive coccidioidomycosis following administration of transfer factor

Three patients with progressive coccidioidomycosis were given preparations of transfer factor (TF). Adverse reactions to TF were minimal. Following TF administration two of these patients had prolonged clinical remissions in their coccidioidal disease. Cellular immune responses were sequentially evaluated by coccidioidininduced delayed-type skin tests, lymphocyte blast transformation and macrophage inhibition factor production (MIF). These three patients each exhibited different cellular immune patterns before and after TF administration. Two patients converted their coccidioidin skin tests, and one converted lymphocyte transformation response to coccidioidin. Also, TF apparently favorably affected the MIF response in all three patients.     

The effects of desiccation and rehydration on the lone star tick

This study describes the effects of desiccation and rehydration on the water content, haemolymph volume (per cent), osmolarity, and concentrations of Na, K, Mg, and Ca in the haemolymph of the lone star tick, Amblyomma americanum.The water content percentages of ‘severely desiccated’, ‘moderately’ and ‘fully hydrated’ ticks were 46·0, 52·8, and 60·3 per cent respectively. The lowest and highest of these were near the minimum and maximum possible.The haemolymph volume (per cent) of ‘severely desiccated’ ticks was regulated near the level of ‘moderately hydrated’ ticks despite significant decreases in total body water content and increases in osmolarity and concentration of sodium. Conversely, the change from ‘severely desiccated’ to ‘moderately hydrated’ ticks can be viewed as causing an increase in total body water, decrease in blood osmolarity and sodium, but little change in haemolymph volume (per cent).Most of the water taken up by ‘moderately hydrated’ ticks (while becoming ‘fully hydrated’) was added to the haemolymph. At the same time, there was little change in the blood osmolarity or haemolymph concentration of sodium. Conversely, the change of ‘fully’ to ‘moderately hydrated’ ticks was marked by a substantial loss of haemolymph volume (per cent) but little change in osmolarity and concentration of sodium.The concentration of potassium was regulated over the full range of desiccating and hydrating conditions. The lone star tick appeared less able to regulate its haemolymph concentrations of Ca and Mg; both fluctuated at the same rate, but inversely as the haemolymph volume (per cent).It appears that a carefully controlled movement of solutes (Na the predominant cation) between haemolymph and non-haemolymph tissue is intimately linked with haemolymph volume regulation and movement of water into the haemolymph during hydration.     

Properties of thylakoids and thylakoid particles derived from structurally different chloroplasts

Structurally and functionally different tobacco chloroplasts were subjected to digitonin treatment and subsequent fractional centrifugation. The light-harvesting $\text{chlorophyll}\text{a}\text{chlorophyll}\text{b-}\text{protein}$ complex was found to be enriched in the most dense fraction regardless of the presence of grana in the original preparation. It is suggested that isolated thylakoid membranes and fragments thereof which contain sufficient light-harvesting protein may, under appropriate ionic conditions, form aggregates even when they originate from unstacked thylakoid systems. Comparative studies of fluorescence properties and polypeptide composition of the thylakoids suggest that the light-harvesting protein does not contribute significantly to the fluorescence spectrum of isolated chloroplasts as long as this protein is intimately associated with the Photosystem II (PS II) pigment-protein complex responsible for the 685 nm emission. While the PS II-deficient mutant chloroplasts of the variegated tobacco variety NC 95 lacked both the 685 nm fluorescence component and two or three PS II proteins, one of these proteins was found to be very prominent in our chlorophyll b-deficient mutant thylakoids which also displayed an intense 685 nm fluorescence peak. This correlation supports the contention that a 45 kdalton polypeptide is an apoprotein of pigments associated with the PS II reaction center.     

The Return of the Phoenix: The 1963 International Congress of Zoology and American Zoologists in the Twentieth Century

This paper examines the International Congress of Zoology held in Washington D.C. in 1963 as a portrait of American zoologists’ search for effective and rewarding relationships with both each other and the public. Organizers of the congress envisioned the congress as a last ditch effort to unify the disparate subdisciplines of zoology, overcome the barriers of specialization, and ward off the heady claims of more reductionist biologists. The problems zoologists faced as they worked to fulfill these ambitious goals illuminate some of the challenges faced by members of the naturalist tradition as they worked to establish disciplinary unity while seeking public support in the competitive world of twentieth century science.     

Photosynthesis research: advances through molecular biology – the beginnings, 1975–1980s and on...

Restriction endonuclease recognition sites and genes for rRNAs were first mapped on chloroplast chromosomes in 1975–1976. This marked the beginning of the application of molecular biology tools to photosynthesis research. In the first phase, knowledge about proteins involved in photosynthesis was used to identify plastid and nuclear genes encoding these proteins on cloned segments of DNA. Soon afterwards the DNA sequences of the cloned genes revealed the full primary sequences of the proteins. Knowledge of the primary amino acid sequences provided deeper understanding of the functioning of the protein and interactions among proteins of the photosynthetic apparatus. Later, as chloroplast DNA sequencing proceeded, genes were discovered that encoded proteins that had not been known to be part of the photosynthetic apparatus. This more complete knowledge of the composition of reaction centers and of the primary amino acid sequences of individual proteins comprising the reaction centers opened the way to determining the three-dimensional structures of reaction centers. At present, the availability of cloned genes, knowledge of the gene sequences and systems developed to genetically manipulate photosynthetic organisms is permitting experimental inquiries to be made into crucial details of the photosynthetic process. This revised version was published online in August 2006 with corrections to the Cover Date.