Expanded thermal niche for a diving vertebrate: A leatherback turtle diving into near-freezing water

The global distribution of extant reptiles is more limited than that of mammals or birds, with low reptilian species diversity at high latitudes. Central to this limited geographical distribution is the ectothermic nature of reptiles, which means that they generally become torpid at cold temperatures. However, here we report the first detailed telemetry from a leatherback turtle (Dermochelys coriacea) diving in cold water at high latitude. An individual equipped with a satellite tag that relayed temperature-depth profiles dived continuously for many weeks into sub-surface waters as cold as 0.4 °C. Global warming will likely increase the foraging range of leatherback turtles further into temperate and boreal waters.     

Diet changes in the carbon and nitrogen content of the copepod Metridia lucens

Diel changes in the near-surface (0–50 m) abundance, prosomelength, and carbon and nitrogen content of the copepod Metridialucens were measured in Deep Cove, Doubtful Sound, New Zealand(45°27'S, 167°9'E) between 3 and 6 September 1996. Metridialucens showed maximal abundance a night, suggesting a patternof normal diel vertical migration (DVM). The change in abundancesuggested that the descent of the population occurred –1h prior to dawn and the ascent –1 h after dusk. However,a proportion of the population remained near the surface duringthe day. Although there was no diel pattern in the prosome lengthof M.lucens collected near the surface, there was a marked dielcycle in the measured carbon and nitrogen contents, with maximalvalues being measured towards the end of the night prior tothe downward migration. We suggest that this diet cycle in themeasured elemental content was caused by DVM occurring morestrongly in those animals which had a better body condition,i.e. a higher elemental content per unit length.     

Interacting proteins identified by genetic interactions: a missense mutation in alpha-tubulin fails to complement alleles of the testis-specific beta-tubulin gene of Drosophila melanogaster.

In this paper we demonstrate that failure to complement between mutations at separate loci can be used to identify genes that encode interacting structural proteins. A mutation (nc33) identified because it failed to complement mutant alleles of the gene encoding the testis-specific beta 2-tubulin of Drosophila melanogaster (B2t) did not map to the B2t locus. We show that this second-site noncomplementing mutation is a missense mutation in alpha-tubulin that results in substitution of methionine in place of valine at amino acid 177. Because alpha- and beta-tubulin form a heterodimer, our results suggest that the genetic interaction, failure to complement, is based on the structural interaction between the protein products of the two genes. Although the nc33 mutation failed to complement a null allele of B2t (B2tn), a deletion of the alpha-tubulin gene to which nc33 mapped complemented B2tn. Thus, the failure to complement appears to require the presence of the altered alpha-tubulin encoded by the nc33 allele, which may act as a structural poison when incorporated into either the tubulin heterodimer or microtubules.     

Human thymocytes do not respond to interleukin-2 after removal of mature "bright" CD5 positive cells

Interleukin-2 receptors (IL-2R) are expressed on minor populations of immature and mature human thymocytes. These studies were designed to determine if immature T cells could respond to the mitogen phytohemagglutinin (PHA-P) plus IL-2 in vitro by increasing the expression of IL-2R and by proliferation. Using monoclonal antibodies to CD5 and magnetic immunobeads we were able to remove all mature, "bright" CD5+ cells from nylon wool-purified thymocytes and to obtain less mature cells which consisted almost completely of cells with the CD4+CD8+ phenotype. These immature cells were mostly "dim" CD5+ and less than 5% CD5- and a small percentage expressed the IL-2R. After culture in serum-free medium with PHA-P, these cells showed only a slight increase in the percentage of IL-2R+ cells and the addition of IL-2 did not increase the percentage of IL-2R+ cells and no proliferation was observed. Unseparated, nylon wool-purified thymocytes contained 14% bright CD5+ cells. These bright CD5+ cells had a mature phenotype of CD4+CD8- (52%) and CD4-CD8+ (27%) cells. A small percentage of these cells were IL-2R+. These bright CD5+IL-2R+ cells were predominantly mature CD4+CD8- cells as measured by three-color flow cytometry. After culture with PHA-P and IL-2, the percentage of IL-2R+ cells increased and they were now found not only on CD4+CD8- but also on CD4-CD8+ and on CD4+CD8+ cells. IL-2 plus PHA-P increased proliferation of these cells as compared to those cultured in medium with PHA-P without IL-2. Thus, we show that human immature thymocytes in contrast to mature thymocytes are not responsive to IL-2 as measured by a lack of IL-2R expression and proliferation. These data indicate that mature thymocytes can express a functional high affinity receptor for IL-2 and suggest that immature thymocytes may not possess a (functional) p75 chain of the IL-2R.     

Duchenne muscular dystrophy: deficiency of dystrophin at the muscle cell surface

Dystrophin is the altered gene product in Duchenne muscular dystrophy (DMD). We used polyclonal antibodies against dystrophin to immunohistochemically localize the protein in human muscle. In normal individuals and in patients with myopathies other than DMD, dystrophin was localized to the sarcolemma of the fibers. The protein was absent or markedly deficient in DMD. The sarcolemmal localization of dystrophin is consistent with other evidence that there are structural and functional abnormalities of muscle surface membranes in DMD.     

Fast muscle fibers are preferentially affected in Duchenne muscular dystrophy

We show that Duchenne muscular dystrophy (DMD) selectively affects a subset of skeletal muscle fibers specialized for fast contraction. Muscle fiber types were characterized immunohistochemically with monoclonal antibodies that distinguish isoforms of fetal and adult-fast or adult-slow myosin heavy chain present in the same fiber. Fetal myosin expression increased with patient age and was not due to arrested development but rather to de novo synthesis, which served as a sensitive indicator of muscle regeneration. A subset of fast fibers were the first to degenerate (type IIb). Extensive fast fiber regeneration occurred before slow fibers were affected. These results suggest that the DMD gene product has a specific function in a subpopulation of muscle fibers specialized to respond to the highest frequency of neuronal stimulation with maximal rates of contraction.     

The structure and evolution of the spider monkey delta-globin gene

We have isolated the delta-globin gene of the New-World spider monkey, Ateles geoffroyi, and compared its nucleotide sequence with those of other primate delta- and beta-globin genes. Among primate delta-globin genes, the rate of nonsynonymous substitutions is much less than the rate of synonymous substitutions. This suggests that primate delta- globin genes may remain under evolutionary conservation, perhaps because hemoglobin A2 has an as yet unknown physiological importance.