From bone biology to bone analysis

Bone development is one of the key processes characterizing childhood and adolescence. Understanding this process is not only important for physicians treating pediatric bone disorders, but also for clinicians and researchers dealing with postmenopausal and senile osteoporosis. Bone densitometry has great potential to enhance our understanding of bone development. The usefulness of densitometry in children and adolescents would be increased if the physiological mechanisms and structural features of bone were given more consideration in the design and interpretation of densitometric studies. This review gives an overview on the most relevant techniques of quantitative noninvasive bone analysis. Furthermore it describes the relationship between bone biology, selected surrogates describing the biological processes and the possibilities of measuring these surrogates specifically and precisely by the different devices. The overall recommendation for researchers in this field is to describe firstly the biological process to be analyzed (bone growth in length, remodeling or modeling, or all together), secondly the bone parameter which describes this process, and thirdly the reason for selecting a special device.     

Approaches to chemical synthetic biology

Synthetic biology is first represented in terms of two complementary aspects, the bio-engineering one, based on the genetic manipulation of extant microbial forms in order to obtain forms of life which do not exist in nature; and the chemical synthetic biology, an approach mostly based on chemical manipulation for the laboratory synthesis of biological structures that do not exist in nature. The paper is mostly devoted to shortly review chemical synthetic biology projects currently carried out in our laboratory. In particular, we describe: the minimal cell project, then the "Never Born Proteins" and lastly the Never Born RNAs. We describe and critically analyze the main results, emphasizing the possible relevance of chemical synthetic biology for the progress in basic science and biotechnology.     

Evaluation of 24-hour growth hormone spontaneous secretion: comparison with a nocturnal and diurnal 12-hour study

Spontaneous growth hormone (GH) secretion in 116 short children was studied by sampling blood for GH measurement every 20 min over 24 h. We calculated 24-h mean GH concentration (MGHC), diurnal 12-h MGHC (dMGHC) and nocturnal 12-h MGHC (nMGHC). The children were subdivided into four groups: prepubertal children with 'classical' GH deficiency (group 1, n = 12, low responses to two provocative stimuli tests and MGHC less than 3 ng/ml), prepubertal children with 'nonclassical' GH deficiency (group 2, n = 36, normal GH responses to two provocative tests and MGHC less than 3 ng/ml), short normal children (normal GH responses to two provocative tests and MGHC greater than 3 ng/ml) at stage P1 of puberty (group 3, n = 41) and at stage P2 of puberty (group 4, n = 27). The values of MGHC, dMGHC and nMGHC were significantly higher in groups 3 and 4 than in groups 1 and 2, and in group 4 than in group 3. The values of MGHC and nMGHC were significantly higher in group 2 than in group 1. MGHC correlated highly with nMGHC and dMGHC (r = 0.97 and 0.94, respectively; p less than 0.001). On the basis of regression equations between MGHC and nMGHC or dMGHC, the study of the diagnostic accuracy showed values higher for nMGHC than for dMGHC: 94.1 vs. 89.6% for sensitivity, and 93.7 vs. 89.7% for specificity, respectively.     

Aminoacylation and translational quality control strategy employed by leucyl-tRNA synthetase from a human pathogen with genetic code ambiguity

Aminoacyl-tRNA synthetases should ensure high accuracy in tRNA aminoacylation. However, the absence of significant structural differences between amino acids always poses a direct challenge for some aminoacyl-tRNA synthetases, such as leucyl-tRNA synthetase (LeuRS), which require editing function to remove mis-activated amino acids. In the cytoplasm of the human pathogen Candida albicans, the CUG codon is translated as both Ser and Leu by a uniquely evolved CatRNA^Ser(CAG). Its cytoplasmic LeuRS (CaLeuRS) is a crucial component for CUG codon ambiguity and harbors only one CUG codon at position 919. Comparison of the activity of CaLeuRS-Ser⁹¹⁹ and CaLeuRS-Leu⁹¹⁹ revealed yeast LeuRSs have a relaxed tRNA recognition capacity. We also studied the mis-activation and editing of non-cognate amino acids by CaLeuRS. Interestingly, we found that CaLeuRS is naturally deficient in tRNA-dependent pre-transfer editing for non-cognate norvaline while displaying a weak tRNA-dependent pre-transfer editing capacity for non-cognate α-amino butyric acid. We also demonstrated that post-transfer editing of CaLeuRS is not tRNA^Leu species-specific. In addition, other eukaryotic but not archaeal or bacterial LeuRSs were found to recognize CatRNA^Ser(CAG). Overall, we systematically studied the aminoacylation and editing properties of CaLeuRS and established a characteristic LeuRS model with naturally deficient tRNA-dependent pre-transfer editing, which increases LeuRS types with unique editing patterns.     

Association between X-linked hypophosphatemic rickets and Klinefelter's syndrome: effects on growth and body proportion

Growth failure with disproportionate short stature is the major clinical feature of patients with X-linked hypophosphatemic rickets (HYP). We studied the pattern of linear growth and body proportion in an untreated normally growing HYP child also affected by Klinefelter's syndrome. Auxologic data were compared with those of a HYP half-brother who showed growth failure despite long-term treatment either with vitamin D or with vitamin-D-analog plus phosphate salt supplementation. The degree of body disproportion changed from negative values to positive values in the proband, whereas it was reduced in the half-brother. We conclude that, in the proband, the normal pattern of growth and the lack of the typical body disproportion as seen in HYP patients are attributable to the concomitant presence of Klinefelter's syndrome.     

Hypophosphataemic rickets

X-Linked hypophosphataemic rickets (XLH) is frequently associated with short stature even when conventional treatment (1, 25-dihydroxyvitamin D(3) or 1alpha-hydroxyvitamin D(3) plus inorganic phosphate salts) is administered for a long time. The pathogenesis of growth retardation is probably multifactorial. Affected patients usually show normal growth hormone (GH) secretion. In some poorly growing XLH patients, long-term GH treatment associated with conventional therapy improves linear growth. GH treatment also increases phosphate retention but this effect is transient.