Synthesis of polyhydroxyalkanoate in the peroxisome of Saccharomyces cerevisiae by using intermediates of fatty acid beta-oxidation.

Medium-chain-length polyhydroxyalkanoates (PHAs) are polyesters having properties of biodegradable thermoplastics and elastomers that are naturally produced by a variety of pseudomonads. Saccharomyces cerevisiae was transformed with the Pseudomonas aeruginosa PHAC1 synthase modified for peroxisome targeting by the addition of the carboxyl 34 amino acids from the Brassica napus isocitrate lyase. The PHAC1 gene was put under the control of the promoter of the catalase A gene. PHA synthase expression and PHA accumulation were found in recombinant S. cerevisiae growing in media containing fatty acids. PHA containing even-chain monomers from 6 to 14 carbons was found in recombinant yeast grown on oleic acid, while odd-chain monomers from 5 to 15 carbons were found in PHA from yeast grown on heptadecenoic acid. The maximum amount of PHA accumulated was 0.45% of the dry weight. Transmission electron microscopy of recombinant yeast grown on oleic acid revealed the presence of numerous PHA inclusions found within membrane-bound organelles. Together, these data show that S. cerevisiae expressing a peroxisomal PHA synthase produces PHA in the peroxisome using the 3-hydroxyacyl coenzyme A intermediates of the beta-oxidation of fatty acids present in the media. S. cerevisiae can thus be used as a powerful model system to learn how fatty acid metabolism can be modified in order to synthesize high amounts of PHA in eukaryotes, including plants.

Gender differences in the human cerebral cortex: more neurons in males; more processes in females.

This study's objective was to investigate morphometric gender differences of the cerebral cortex in six males and five females, 12 to 24 years old. Though human brains lack sexual dimorphism on routine neuropathologic examinations, gender-specific brain weight, functional, and morphologic differences exist, suggesting that cortical differences may be found. Yet the cerebral cortex may be exempt from gender differences, as demonstrated by the fact that normal males and females perform comparably on intelligence tests. Stereologic morphometry on standardized histologic sections from 30 bilateral cortical loci determined cortical thickness, neuronal density, and derived neuronal number estimates. The mean +/- SD cortical thickness of the 60 loci examined was similar in males and females with right and left hemispheric gender ratios being balanced. In contrast, the average neuronal density of the same 60 loci was significantly higher in the male group than in the female group, and the corresponding mean male-to-female ratios were 1.18 in the right and 1.13 in the left hemisphere, which differ significantly from each other and from the balanced cortical thickness ratios. Estimates of neuronal numbers -- the product of neuronal thickness times density -- were 13% higher in males than in females, with mean male-to-female ratios of 1.13 in both hemispheres. The data provide morphologic evidence of considerable cerebral cortical dimorphism with the demonstration of significantly higher neuronal densities and neuronal number estimates in males, though with similar mean cortical thickness, implying a reciprocal increase in neuropil/neuronal processes in the female cortex.

Human cortex development: estimates of neuronal numbers indicate major loss late during gestation.

This morphometric study explores temporal and topographic changes in the estimated neuronal number in human neocortex during the latter half of gestation and early infancy. Neuronal estimates are calculated from standardized measurements of cortical layer thickness and neuronal density in 6 neocortical regions in 9 human brains ranging from 17 weeks of gestation to 13 weeks postnatally. Layer thickness increases linearly with age while the average neuronal density first increases, then reaches a maximum at 20 weeks of gestation, and progressively declines. The sum of layer thickness times layer density estimates the number of neurons in a cortical column with a fixed surface area and a length that is equal to the cortical thickness. To derive an estimate of potentially overproduced neurons, the number of neurons in each cortical column was corrected for surface growth and for cortex gyration. These data show that a large percent of cortical neurons present at 20 weeks of gestation are used to populate the expanding cortex. Nevertheless, the growth-corrected data suggest that a substantial overproduction and secondary reduction of cortical neurons takes place mainly during the last quarter of gestation. The corrected mean number of neurons reaches a maximum at 28 weeks of gestation and then declines by approximately 70% to achieve a stable number of neurons around birth. This estimated number of neurons is significantly higher at 28 to 32 weeks of gestation than at 17 to 20 gestational weeks and at 0 to 13 postnatal weeks. These data imply that physiologic neuronal death (apoptosis) may play a major role in early human cortex development.