Skeletal Ultrastructure in some Tubuliporine Cyclostome Bryozoans

The ultrastructure of the calcareous skeleton is described in twenty–one species of recent tubuliporine cyclostome bryozoans, using field emission SEM. The succession of skeletal fabrics in interior walls may be classified into four different fabric suites. The first–formed part of the calcitic skeleton in all species for which it has been observed is a precursory fabric of tiny, wedge–shaped crystallites. This is succeeded in about half of the species studied by a fabric of transverse fibres, followed by foliated fabric and often semi–nacre (fabric suite 1). Most of the remaining species lack transverse fibres and have interior walls largely comprising semi–nacre (fabric suite 2). A few species have skeletons consisting of predominantly distally–oriented, irregularly or regularly foliated fabric (fabric suite 3). A single species has a skeleton of proximally–oriented foliated fabric (fabric suite 4). Basal exterior walls in all species have a precursory fabric of tiny wedge–shaped crystallites without a strong preferred orientation, deposited directly upon the organic cuticle, followed by a layer of planar spherulitic structure, which in turn is succeeded by a similar fabric to that developed in the interior wall of the species concerned. Outermost layers of frontal exterior walls exhibit one of the following combinations of three fabrics: an outer layer of (1) finely granular or wedge–shaped crystallites; a thin dense granular layer followed by (2) distally accreting planar spherulitic fabric., or (3) obliquely accreting planar spherulitic fabric growing partly towards the midline of the frontal wall. Terminal diaphragms usually have outer layers dominated by planar spherulitic ultrastructure with centripetal growth directions. The fabric suites present in tubuliporines encompass most known fabrics found in the other cyclostome suborders and support the notion that this species–rich suborder occupies a central position in cyclostome evolution.     

Polymorphic Admixture Typing in Human Ethnic Populations

A panel of 257 RFLP loci was selected on the basis of high heterozygosity in Caucasian DNA surveys and equivalent spacing throughout the human genome. Probes from each locus were used in a Southern blot survey of allele frequency distribution for four human ethnic groups: Caucasian, African American, Asian (Chinese), and American Indian (Cheyenne). Nearly all RFLP loci were polymorphic in each group, albeit with a broad range of differing allele frequencies (δ). The distribution of frequency differences (δ values) was used for three purposes: (1) to provide estimates for genetic distance (differentiation) among these ethnic groups, (2) to revisit with a large data set the proportion of human genetic variation attributable to differentiation within ethnic groups, and (3) to identify loci with high δ values between recently admixed populations of use in mapping by admixture linkage disequilibrium (MALD). Although most markers display significant allele frequency differences between ethnic groups, the overall genetic distances between ethnic groups were small (.066–.098), and <10% of the measured overall molecular genetic diversity in these human samples can be attributed to “racial” differentiation. The median δ values for pairwise comparisons between groups fell between .15 and .20, permitting identification of highly informative RFLP loci for MALD disease association studies.     

Defective Fc-mediated phagocytosis in C3H/HeJ macrophages. II. Correction by cAMP agonists

Peritoneal macrophages from LPS hyporesponsive C3H/HeJ mice lose the capacity to bind and phagocytose opsonized sheep erythrocytes (EA) over a 48-hr culture period. This loss in Fc receptor capacity is markedly different from the progressive increase in phagocytic ability exhibited by cultured macrophages derived from LPS-responsive C3H/HeN mice. Since dibutyryl-cyclic adenosine monophosphate (DBcAMP) has previously been reported to modulate membrane receptor expression in lymphocytes and certain macrophage-like cell lines, we examined its effects on EA binding and phagocytosis by C3H/HeJ macrophages. DBcAMP not only reverses the binding defect in C3H/HeJ macrophages but also restores EA phagocytosis to the level of control C3H/HeN cultures. 8-Bromo-cAMP, as well as other agents known to elevate intracellular cAMP (i.e., isoproterenol plus isobutylmethylxanthine or prostaglandin E2) also corrected the phagocytic defect. Since the C3H/HeJ macrophage phagocytic defect can also be reversed by in vitro stimulation with a lymphokine-rich culture supernatant, we examined the effect of this treatment on intracellular cAMP levels. Lymphokine treatment produced a 60% increase in the levels of macrophage intracellular cAMP. These findings suggest that the C3H/HeJ differentiation defect may be secondary to some abnormality in a cAMP dependent pathway.     

Skeletal Ultrastructure of the Early Astogenetic Stages of Some Cyclostome Bryozoans

The calcific protoecia of cyclostome bryozoans have remarkably uniform skeletal ultrastructure in three suborders (Tubuliporina, Cancellata and Rectangulata). The basal wall or floor has a fine outer granular layer succeeded by planar spherulitic fabric, internally lined by irregular semi-nacre. The roof of the disc comprises an outer granular layer with an inner lining of semi-nacre continuous with that of the floor; planar spherulitic fabric is absent. Growth of the floor of the disc is initiated around the circular outer rim and continues centripetally to the centre; the inner lining has no prevailing growth direction. The gently domed roof also initiates around the outer rim, and grows in strips, which grow toward the centre, then distally toward the distal tube of the ancestrula which has a fully adult ultrastructure. Protoecia] ultrastructure is independent of adult ultrastructure. The uniformity of skeletal ultrastructure in cyclostomes corresponds with the close similarity of larvae and post-settlement metamorphosis in the order. The fabric suite of the protoecium resembles the skeletal ultrastructure of Palaeozoic stenolaemates. The primitive fabric condition is retained by some tubuliporines and cancellates. Complex multilayered fabric suites may have evolved in the Mesozoic by addition of new fabric types.     

Orbital forcing and the spread of C4 grasses in the late Neogene: stable isotope evidence from South African speleothems

Reconstructing Plio-Pleistocene African paleoenvironments is important for models of early hominin evolution, but is often hampered by low-resolution or discontinuous climatic data. Here, we present high-resolution stable oxygen and carbon isotope time series data from two flowstones (secondary cave deposits) from the South African hominin-bearing Makapansgat Valley. The age of the older of the two flowstones (Collapsed Cone) is constrained by magnetostratigraphy to approximately 4-5 Ma; the younger flowstone (Buffalo Cave) grew between 2.0-1.5 Ma, as determined by magnetostratigraphy and orbital tuning of the isotopic data. The carbon isotope data is used as a proxy for the proportion of C(4) grasses in the local environment and the oxygen isotope data reflects monsoon rainfall intensity. The carbon isotope evidence indicates that in the late Miocene/early Pliocene, the local environment was dominated by C(3) vegetation, whereas, in the Plio-Pleistocene, it was composed of a mixture of C(3) and C(4) vegetation. This suggests that C(4) grasses became a significant part of the Makapansgat Valley ecosystem at approximately 4-5 Ma, towards the end of the late Neogene global expansion of C(4) grasses. After this initial expansion, South Africa experienced further fluctuations in the proportion of C(3) and C(4) vegetation during the Plio-Pleistocene, in response to regional and global climatic changes. Most notably, the Buffalo Cave flowstone provides evidence for C(4) grass expansion at ca. 1.7 Ma that we suggest was a response to African aridity caused by the onset of the Walker Circulation in the Pacific Ocean at this time.     

Type 2 diabetes TCF7L2 risk genotypes alter birth weight: a study of 24,053 individuals

The role of genes in normal birth-weight variation is poorly understood, and it has been suggested that the genetic component of fetal growth is small. Type 2 diabetes genes may influence birth weight through maternal genotype, by increasing maternal glycemia in pregnancy, or through fetal genotype, by altering fetal insulin secretion. We aimed to assess the role of the recently described type 2 diabetes gene TCF7L2 in birth weight. We genotyped the polymorphism rs7903146 in 15,709 individuals whose birth weight was available from six studies and in 8,344 mothers from three studies. Each fetal copy of the predisposing allele was associated with an 18-g (95% confidence interval [CI] 7-29 g) increase in birth weight (P=.001) and each maternal copy with a 30-g (95% CI 15-45 g) increase in offspring birth weight (P=2.8x10-5). Stratification by fetal genotype suggested that the association was driven by maternal genotype (31-g [95% CI 9-48 g] increase per allele; corrected P=.003). Analysis of diabetes-related traits in 10,314 nondiabetic individuals suggested the most likely mechanism is that the risk allele reduces maternal insulin secretion (disposition index reduced by ~0.15 standard deviation; P=1x10-4), which results in increased maternal glycemia in pregnancy and hence increased offspring birth weight. We combined information with the other common variant known to alter fetal growth, the -30G-->A polymorphism of glucokinase (rs1799884). The 4% of offspring born to mothers carrying three or four risk alleles were 119 g (95% CI 62-172 g) heavier than were the 32% born to mothers with none (for overall trend, P=2x10-7), comparable to the impact of maternal smoking during pregnancy. In conclusion, we have identified the first type 2 diabetes-susceptibility allele to be reproducibly associated with birth weight. Common gene variants can substantially influence normal birth-weight variation.