SEPALLATA3: the 'glue' for MADS box transcription factor complex formation

Background  

Plant MADS box proteins play important roles in a plethora of developmental processes. In order to regulate specific sets of target genes, MADS box proteins dimerize and are thought to assemble into multimeric complexes. In this study a large-scale yeast three-hybrid screen is utilized to provide insight into the higher-order complex formation capacity of the Arabidopsis MADS box family. SEPALLATA3 (SEP3) has been shown to mediate complex formation and, therefore, special attention is paid to this factor in this study.     

Purine phosphoribosyltransferase (EC 2.4.2.7 and 2.4.2.8) and purine de novo synthesis activity in rat testicular tissue at different stages of development, and their correlation with the circulating levels of gonadotrophins and testosterone, and with structural changes

The overall activity of the purine de novo synthesis pathway and the activities of purine phosphoribosyltransferase in the rat testis were measured at different ages and were correlated with histological observations. Similar studies of the concentration of circulating gonadotrophins and testosterone were performed. The purine phosphoribosyltransferase activities were between two and three orders of magnitude greater than purine de novo synthesis. The peak activity of the purine de novo synthesis pathway coincided with the first appearance of meiosis in the spermatocytes immediately before the luteinising hormone (LH) level rose to its peak. The highest activity of the hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8) - catalysed purine salvage pathway coincided with the first appearance of mature spermatozoa in the tubules just after the occurrence of peak levels of follicle-stimulating hormone (FSH). These findings are linked to the development of testicular atrophy in cases of severe HPRT deficiency in man.     

Hydrogen peroxide is generated during the very early stages of aggregation of the amyloid peptides implicated in Alzheimer disease and familial British dementia

Alzheimer disease and familial British dementia are neurodegenerative diseases that are characterized by the presence of numerous amyloid plaques in the brain. These lesions contain fibrillar deposits of the beta-amyloid peptide (Abeta) and the British dementia peptide (ABri), respectively. Both peptides are toxic to cells in culture, and there is increasing evidence that early "soluble oligomers" are the toxic entity rather than mature amyloid fibrils. The molecular mechanisms responsible for this toxicity are not clear, but in the case of Abeta, one prominent hypothesis is that the peptide can induce oxidative damage via the formation of hydrogen peroxide. We have developed a reliable method, employing electron spin resonance spectroscopy in conjunction with the spin-trapping technique, to detect any hydrogen peroxide generated during the incubation of Abeta and other amyloidogenic peptides. Here, we monitored levels of hydrogen peroxide accumulation during different stages of aggregation of Abeta-(1-40) and ABri and found that in both cases it was generated as a short "burst" early on in the aggregation process. Ultrastructural studies with both peptides revealed that structures resembling "soluble oligomers" or "protofibrils" were present during this early phase of hydrogen peroxide formation. Mature amyloid fibrils derived from Abeta-(1-40) did not generate hydrogen peroxide. We conclude that hydrogen peroxide formation during the early stages of protein aggregation may be a common mechanism of cell death in these (and possibly other) neurodegenerative diseases.     

A dimensionless invariant for relative size at sex change in animals: explanation and implications

Recent comparative studies across sex-changing animals have found that the relative size and age at sex change are strikingly invariant. In particular, 91%-97% of the variation in size at sex change across species can be explained by the simple rule that individuals change sex when they reach 72% of their maximum body size. However, this degree of invariance is surprising and has proved controversial. In particular, it is not clear why this result should hold, given that there is considerable biological variation across species in factors that can influence the evolutionarily stable timing of sex change. Our overall aim here is to explain this result and determine the implications for other life-history variables. Specifically, we use a combination of approaches to formalize and make explicit previous analytical theory in this area, examine the robustness of the empirical invariance result, and carry out sensitivity analyses to determine what the empirical data imply about the mean value and variation in several key life-history variables.     

A spectroscopic study of some of the peptidyl radicals formed following hydroxyl radical attack on beta-amyloid and alpha-synuclein

There is clear evidence implicating oxidative stress in the pathology of many neurodegenerative diseases. Reactive oxygen species (ROS) are the primary mediators of oxidative stress, and hydrogen peroxide, a key ROS, is generated during aggregation of the amyloid proteins associated with some of these diseases. Hydrogen peroxide is catalytically converted to the aggressive hydroxyl radical in the presence of Fe(II) and Cu(I), which renders amyloidogenic proteins such as beta-amyloid and alpha-synuclein (implicated in Alzheimer's disease (AD) and Parkinson's disease (PD), respectively) vulnerable to self-inflicted hydroxyl radical attack. Here, we report some of the peptide-derived radicals, detected by electron spin resonance spectroscopy employing sodium 3,5-dibromo-4-nitrosobenzenesulfonate as a spin-trap, following hydroxyl radical attack on Abeta(1-40), alpha-synuclein and some other related peptides. Significantly, we found that sufficient hydrogen peroxide was self-generated during the early stages of aggregation of Abeta(1-40) to produce detectable peptidyl radicals, on addition of Fe(II). Our results support the hypothesis that oxidative damage to Abeta (and surrounding molecules) in the brain in AD could be due, at least in part, to the self-generation of ROS. A similar mechanism could operate in PD and some other "protein conformational" disorders.     

Utilization of a multiple antigenic peptide as a calibration standard in the BAN50 single antibody sandwich ELISA for Aβ oligomers

Soluble amyloid-β (Aβ) oligomers are thought to be a cause of neurodegeneration and memory loss in Alzheimer disease (AD). We recently reported a newly developed enzyme linked immunosorbent assay (ELISA) for high molecular weight (HMW) Aβ oligomers in which the same Aβ monoclonal antibody, BAN50, was used for both capture and detection in a single antibody sandwich ELISA (SAS-ELISA) system. Our previous data suggest that this assay will be useful for the early diagnosis of AD, but its practical application to large-scale or longitudinal studies has been limited because of lack of a reliable calibration standard. In order to develop such a standard, we have now constructed a novel peptide using the multiple antigenic peptide (MAP) technique, where multiple epitopes of BAN50 were linked, via a spacer, to a branching lysine core. We show that the standard curve constructed from a 16-mer MAP covered the physiological range of signals obtained in the BAN50 SAS-ELISA from samples of human CSF, serum, and plasma. Furthermore, this 16-mer MAP is available in large quantities and is stable against freeze-thawing. We estimate that the signal per 1 pM of this standard corresponds to 1.54-5.0 pM of HMW Aβ oligomers. This MAP approach could also be used to provide an effective calibration standard for other SAS-ELISAs.     

Responses to the lowering of magnesium and calcium concentrations in the cerebrospinal fluid of unanesthetized sheep.

A technique for ventriculolumbar perfusion of the cerebrospinal fluid space has been used to study the neuromuscular effects of low concentrations of magnesium and calcium in the cerebrospinal fluid of conscious sheep. Perfusion with synthetic cerebrospinal fluid solutions containing less than 0-6 mg magnesium/100 ml produced episodes of tetany which were abolished by perfusion with a solution of normal magnesium concentration. This suggests that the low cerebrospinal fluid magnesium concentrations reported in cases of hypomagneseamic tetany may result in changes within the central nervous system that could produce the nervous signs. Perfusates with a calcium concentration below 2-0 mg/100 ml caused hyperpnoea and continuous muscle tremors. Magnesium (0-6 mg/100 ml) and calcium (2-0 mg/100 ml) perfused simultaneously acted synergistically to produce signs characteristic of low levels of each of the ions.