Xanthine oxidase is a peroxynitrite synthase: newlyidentified roles for a very old enzyme

Abstract

Several investigators have generated long-lived nematode worms (Caenorhabditis elegans) in the past decade by mutation of genes in the organism in order to study the genetics of aging and longevity. Dozens of longevity assurance genes (LAG) that dramatically increase the longevity of this organism have been identified. All long-lived mutants of C. elegans are also resistant to environmental stress, such as high temperature, reactive oxygen species (ROS), and ultraviolet irradiation. Double mutations of some LAGs further extended life span up to 400%, providing more insight into cellular mechanisms that put limits on the life span of organisms. With the availability of the LAG mutants and the combined DNA microarray and RNAi technology, the understanding of actual biochemical processes that determine life span is within reach: the downstream signal transduction pathway may regulate life span by up-regulating pro-longevity genes such as those that encode antioxidant enzymes and/or stress-response proteins, and down-regulating specific life-shortening genes. Furthermore, longevity could be modified through chemical manipulation. Results from these studies further support the free radical theory of aging, suggest that the molecular mechanism of aging process may be shared in all organisms, and provide insight for therapeutic intervention in age-related diseases.     

HOXA10 and HOXA13 sequence variations in human female genital malformations including congenital absence of the uterus and vagina

Congenital genital malformations occurring in the female population are estimated to be 5 per 1000 and associate with infertility, abortion, stillbirth, preterm delivery and other organ abnormalities. Complete aplasia of the uterus, cervix and upper vagina (Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome) has an incidence of 1 per 4000 female live births. The molecular etiology of congenital genital malformations including MRKH is unknown up to date. The homeobox (HOX) genes HOXA10 and HOXA13 are involved in the development of human genitalia. In this investigation, HOXA10 and HOXA13 genes of 20 patients with the MRKH syndrome, 7 non-MRKH patients with genital malformations and 53 control women were sequenced to assess for DNA variations. A total of 14 DNA sequence variations (10 novel and 4 known) within exonic and untranslated regions were detected in HOXA10 and HOXA13 among our cohorts. Four HOXA10 and two HOXA13 DNA sequence variations were found solely in patients with genital malformations. In addition to mutations resulting in synonymous amino acid substitutions, in the HOXA10 gene a missense mutation was identified and predicted by computer analysis as probably damaging to protein function in two non-MRKH patients, one with a bicornate and the other patient with a septated uterus. A novel exonic HOXA10 cytosine deletion was also identified in a non-MRKH patient with a septate uterus and renal malformations resulting in a premature stop codon and loss of the homeodomain helix 3/4. This cytosine deletion and the missense mutation in HOXA10 were analysed by real time PCR and sequencing, respectively, in two additional larger cohorts of 103 patients with MRKH and 109 non-MRKH patients with genital malformations. No other patients were found with the cytosine deletion however one additional patient was identified regarding the missense mutation. Rare DNA sequence variations in the HOXA10 gene could contribute to the misdevelopment of female internal genitalia.     

The functions of WHIRLY1 and REDOX-RESPONSIVE TRANSCRIPTION FACTOR 1 in cross tolerance responses in plants: a hypothesis

Chloroplasts are important sensors of environment change, fulfilling key roles in the regulation of plant growth and development in relation to environmental cues. Photosynthesis produces a repertoire of reductive and oxidative (redox) signals that provide information to the nucleus facilitating appropriate acclimation to a changing light environment. Redox signals are also recognized by the cellular innate immune system allowing activation of non-specific, stress-responsive pathways that underpin cross tolerance to biotic–abiotic stresses. While these pathways have been intensively studied in recent years, little is known about the different components that mediate chloroplast-to-nucleus signalling and facilitate cross tolerance phenomena. Here, we consider the properties of the WHIRLY family of proteins and the REDOX-RESPONSIVE TRANSCRIPTION FACTOR 1 (RRTF1) in relation to chloroplast redox signals that facilitate the synergistic co-activation of gene expression pathways and confer cross tolerance to abiotic and biotic stresses. We propose a new hypothesis for the role of WHIRLY1 as a redox sensor in chloroplast-to-nucleus retrograde signalling leading to cross tolerance, including acclimation and immunity responses. By virtue of its association with chloroplast nucleoids and with nuclear DNA, WHIRLY1 is an attractive candidate coordinator of the expression of photosynthetic genes in the nucleus and chloroplasts. We propose that the redox state of the photosynthetic electron transport chain triggers the movement of WHIRLY1 from the chloroplasts to the nucleus, and draw parallels with the regulation of NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1).