Dynamics of Bacillus subtilis helical macrofiber morphogenesis: writhing, folding, close packing, and contraction

Helical Bacillus subtilis macrofibers are highly ordered structures consisting of individual cells packed in a geometry remarkably similar to that found in helically twisted yarns (G. A. Carnaby, in J. W. S. Hearle et al., ed., The Mechanics of Flexible Fibre Assemblies, p. 99-112, 1980; N. H. Mendelson, Proc. Natl. Acad. Sci. U.S.A. 75:2478-2482, 1978). The growth and formation of macrofibers were studied with time-lapse microscopy methods. The basic growth mode consisted of fiber elongation, folding, and the helical wrapping together of the folded portion into a tight helical fiber. This sequence was reiterated at both ends of the structure, resulting in terminal loops. Macrofiber growth was accompanied by the helical turning of the structure along its long axis. Right-handed structures turned clockwise and left-handed ones turned counterclockwise when viewed along the length of a fiber looking toward a loop end. Helical turning forced the individual cellular filaments into a close-packing arrangement during growth. Tension was evident within the structures and they writhed as they elongated. Tension was relieved by folding, which occurred when writhing became so violent that the structure touched itself, forming a loop. When the multistranded structure produced by repeated folding cycles became too rigid for additional folding, the morphogenesis of a ball-like structure began. The dynamics of helical macrofiber formation was interpreted in terms of stress-strain deformations. In view of the similarities between macrofiber structures and those found in multifilament yarns and cables, the physics of helical macrofiber structure and also growth may be suitable for analysis developed in these fields concerning the mechanics of flexible fiber assemblies (C. P. Buckley; J. W. S. Hearle; and J. J. Thwaites, in J. W. S. Hearle et al., ed., The Mechanics of Flexible Fibre Assemblies, p. 1-97, 1980).     

Inversion of helix orientation in Bacillus subtilis macrofibers

The ability of helical macrofibers of Bacillus subtilis to convert from left- to right-handed structures or vice versa has been known to be controlled by the nutritional environment (N. H. Mendelson, Proc. Natl. Acad. Sci. U.S.A., 75:2478-2482, 1978). lyt mutants (Ni15, FJ3, FJ6, and FJ7) and also lyt phenocopies of wild-type strain FJ8 were able to undergo helix hand inversion as a function of temperature. The transition between right- and left-handed structures was in a very narrow range (about 2.5 degrees C) in the low to mid-40 degrees C. The helix orientation of these strains was also influenced by the concentration of divalent ions. Macrofiber handedness is governed, therefore, by at least four factors: genetic composition, temperature, and nutritional and ionic environments. Conditions normally used for growth fall, within this matrix, in the region favoring right-handed structures. Inhibition studies suggest that cell growth must occur for helix hand inversion.     

A new mathematical approach predicts individual cell growth behavior using bacterial population information

A theoretical methodology has been developed for studying the growth kinetics of bacterial cells. It utilizes the steady-state cell length distribution in a bacterial population to predict the dependency of growth and division rates on cell length and age. The mathematical model has been applied to the analysis of two bacterial populations, a wild-type strain of Bacillus subtilis, and a minicell-producing strain that carries the divIVB1 mutation. The results show that our model describes the wild-type population very well and that the assumptions typically used in traditional methods are unrealistic. In the case of the minicell-producing mutant we find evidence that the rate of cell division must be a function not only of cell size but also of cell age.     

O2 enhancement of human trophoblast differentiation and hCYP19 (aromatase) gene expression are mediated by proteasomal degradation of USF1 and USF2

When cultured in 20% O(2), human cytotrophoblasts fuse to form the syncytiotrophoblast with marked induction of hCYP19 (aromatase) gene expression. When cultured in 2% O(2), cytotrophoblast fusion and induced hCYP19 expression are prevented. These effects of hypoxia are mediated by increased expression of mammalian achaete/scute homologue-2 (Mash-2), which increases levels of upstream stimulatory factors 1 and 2 (USF1/2) and their binding as heterodimers to E-boxes surrounding the hCYP19 promoter. In studies to define mechanisms for O(2) regulation of syncytiotrophoblast differentiation, we found that hypoxia and overexpression of Mash-2 markedly increased cyclin B1 levels in cultured trophoblasts and the proportion of cells at the G(2)/M transition. Unlike USF proteins, USF1/2 mRNA levels are unaffected by O(2) tension. To determine whether increased O(2) might enhance proteasomal degradation of USF1/2, human trophoblasts were cultured in 2% or 20% O(2) with or without proteasome inhibitors. In cells cultured in 20% O(2), proteasome inhibitors increased USF1/2 protein levels and blocked spontaneous induction of hCYP19 expression, cell fusion, and differentiation. Like hypoxia, inhibitory effects of proteasome inhibitors on hCYP19 expression were mediated by increased binding of USF1/2 to the E-boxes. In human trophoblast cells cultured in 20% O(2), increased polyubiquitylation of USF1/2 proteins was observed. Thus, early in gestation when the placenta is relatively hypoxic, increased USF1/2 may block trophoblast differentiation and hCYP19 gene expression. In the second trimester, increased O(2) tension promotes proteasomal degradation of USF1/2, resulting in syncytiotrophoblast differentiation and induction of hCYP19 expression.     

Insulin resistance in adolescents with Down syndrome: a cross-sectional study

Background

The prevalence of diabetes mellitus is higher in individuals with Down syndrome (DS) than in the general population; it may be due to the high prevalence of obesity presented by many of them. The aim of this study was to evaluate the insulin resistance (IR) using the HOMA (Homeostasis Model Assessment) method, in DS adolescents, describing it according to the sex, body mass index (BMI) and pubertal development.

Methods

15 adolescents with DS (8 males and 7 females) were studied, aged 10 to 18 years, without history of disease or use of medication that could change the suggested laboratory evaluation. On physical examination, the pubertal signs, acanthosis nigricans (AN), weight and height were evaluated. Fasting plasma glucose and insulin were analysed by the colorimetric method and RIA-kit LINCO, respectively. IR was calculated using the HOMA method. The patients were grouped into obese, overweight and normal, according to their BMI percentiles. The EPIINFO 2004 software was used to calculate the BMI, its percentile and Z score.

Results

Five patients were adults (Tanner V or presence of menarche), 9 pubertal (Tanner II – IV) and 1 prepubertal (Tanner I). No one had AN. Two were obese, 4 overweight and 9 normal. Considering the total number of patients, HOMA was 1.7 ± 1.0, insulin 9.3 ± 4.8 μU/ml and glucose 74.4 ± 14.8 mg/dl. The HOMA values were 2.0 ± 1.0 in females and 1.5 ± 1.0 in males. Considering the nutritional classification, the values of HOMA and insulin were: HOMA: 3.3 ± 0.6, 2.0 ± 1.1 and 1.3 ± 0.6, and insulin: 18.15 ± 1.6 μU/ml, 10.3 ± 3.5 μU/ml and 6.8 ± 2.8 μU/ml, in the obese, overweight and normal groups respectively. Considering puberty, the values of HOMA and insulin were: HOMA: 2.5 ± 1.3, 1.4 ± 0.6 and 0.8 ± 0.0, and insulin: 13.0 ± 5.8 μU/ml, 7.8 ± 2.9 μU/ml and 4.0 ± 0.0 μU/ml, in the adult, pubertal and prepubertal groups respectively.

Conclusion

The obese and overweight, female and adult patients showed the highest values of HOMA and insulin.