Concomitant Information in Competing Risk Analysis

A competing risk model, accommodating both Type I censoring and random withdrawals, is expanded to incorporate concomitant information by allowing the parameters of the underlying distributions to be a linear function of two covariates. The model is developed for two competing risks, one following a Weibull distribution and the other a Rayleigh distribution, and random withdrawals following a Weibull distribution. A method is developed for testing the equality of the coefficients for a given covariate for each of the competing risks using MLE'.     

Gelled diet for screwworm (Diptera: Calliphoridae) mass production

A rearing system based on a diet gelled with Water-Lock G-400, a synthetic superabsorbent (poly(2-propenamide-co-2-propenoic acid, sodium salt)) (WL), was compared with the standard rearing system (liquid diet suspended in acetate fibers) for the mass production of screwworms, Cochliomyia hominivorax (Coquerel). The WL rearing system yielded 2% heavier pupae, 32% higher egg to pupa survival, and required 54% less diet and 88% less labor than the standard rearing system. Other advantages of the WL system include reduced susceptibility to suboptimal environmental conditions and labor practices and characteristics conducive to centralization and mechanization of rearing procedures.     

The switch from larval to adult globin gene expression in Xenopus laevis is mediated by erythroid cells from distinct compartments

The transition of hemoglobins during metamorphosis of Xenopus laevis involves replacement of the larval erythrocytes by adult ones, suggesting that the developmental control of this event depends upon the growth characteristics of the precursor cells. To identify the erythroid precursor cells and to investigate their developmental fate, we analyzed the distribution of stage-specific globin mRNAs by northern blotting in dorsal and ventral fragments of stage 32 embryos after in vitro culture as well as presumptive erythropoietic tissues of tadpoles during metamorphosis. The histological analysis shows that erythrocytes differentiate only in ventral fragments, suggesting that the ventral blood islands and most likely also the dorsolateral mesoderm are the primary sites of erythropoiesis. We also demonstrate that the first generations of erythrocytes, already express the predominating larval-specific alpha-globin mRNAs. The globin mRNA patterns obtained from presumptive erythropoietic tissues suggest an important role of circulating precursor cells in larval erythropoiesis, whereas the liver appears to be the main site of formation and maturation of the adult erythrocytes. Tentatively we propose that anuran erythropoiesis is dependent upon a self-perpetuating stem-cell line and that the larval and the adult erythrocytes are derived from successive generations of erythroid precursors, whose commitment may be imposed by the erythropoietic sites.     

A rRNA-mRNA base pairing model for UGA-dependent termination.

A series of site-directed mutations has been constructed in E coli 16S rRNA and shown to suppress UGA-dependent translational termination. With the exception of the C726 to G base change, all were constructed in helix 34. Characterization of these mutations is reviewed here and from these data and mRNA-rRNA base pairing model for the termination event is presented. The interaction functions via antiparallel base pairing between either 1 of the 2 UCA motifs in helix 34 and the complementary UGA stop codon on the message, thus forming a quasicontinuous A-type helical structure that is further stabilized by stacking enthalpy. Finally, rRNA motifs potentially required for UAA and UAG-dependent translational termination are discussed.     

Decarboxylation of branched-chain alpha-ketoacids in hepatocytes from alloxan-diabetic rats. The effect of insulin

The flux through branched-chain alpha-ketoacid dehydrogenase and the activity of the branched-chain alpha-ketoacid dehydrogenase complex were measured in hepatocytes isolated from fed, starved and alloxan diabetic rats. The highest rate of branched-chain alpha-ketoacid oxidation was found in hepatocytes isolated from starved rats, slightly lower in those from fed rats, and significantly lower in diabetic hepatocytes. The amount of the active form of branched-chain alpha-ketoacid dehydrogenase was only slightly diminished in diabetic hepatocytes, whereas the flux through the dehydrogenase was inversely correlated with the rate of endogenous ketogenesis. The same was observed in hepatocytes isolated from starved rats when branched-chain alpha-ketoacid oxidation was measured in the presence of added oleate. In both cases the diminished flux through the dehydrogenase, restored by a short preincubation of hepatocytes with insulin, was paralleled by a decrease of fatty acid-derived ketogenesis. The significance of these findings is discussed in relation to the role of insulin in branched-chain alpha-ketoacid oxidation in liver of diabetic rats.     

A search for quantitative trait loci for ovulation rate in cattle

Seventy-seven polymorphic microsatellites were analysed in offspring of three elite sires that were part of the foundation of an experimental population selected for twinning rate at the US Meat Animal Research Center, Clay Center, Nebraska. All females were assessed for ovulation rate by rectal palpation of corpora lutea over 8–10 consecutive oestrous cycles from approximately 12 to 18 months of age, and associations between ovulation rate and sire allele were examined in each of the three sire groups. A preliminary analysis was performed using selectively genotyped daughters of each sire. Markers found significant or approaching significance were also genotyped in all daughters, sons and granddaughters of these sires. A test of marker associations limited to the granddaughter data provided an independent confirmation of marker effect and significance relative to the initial test with daughter data. Putative ovulation rate quantitative trait loci were detected on chromosomes 7 and 23. Marker UWCA20 on chromosome 7 was associated with an effect in excess of one phenotypic standard deviation and accounted for approximately 10% of phenotypic variation ovulation rate. Marker CYP21 (steroid 21-hydroxylase) on chromosome 23 was associated with an effect of slightly less than half a phenotypic standard deviation and accounted for approximately 4% of phenotypic variation.