A role for LAX2 in regulating xylem development and lateral-vein symmetry in the leaf.

Background and Aims: The symmetry of venation patterning in leaves is highly conserved within a plant species. Auxins are involved in this process and also in xylem vasculature development. Studying transgenic Arabidopsis plants ectopically expressing the sunflower transcription factor HaHB4, it was observed that there was a significant lateral-vein asymmetry in leaves and in xylem formation compared to wild type plants. To unravel the molecular mechanisms behind this phenotype, genes differentially expressed in these plants and related to auxin influx were investigated. Methods: Candidate genes responsible for the observed phenotypes were selected using a co-expression analysis. Single and multiple mutants in auxin influx carriers were characterized by morphological, physiological and molecular techniques. The analysis was further complemented by restoring the wild type (WT) phenotype by mutant complementation studies and using transgenic soybean plants ectopically expressing HaHB4 . Key Results: LAX2 , down-regulated in HaHB4 transgenic plants, was bioinformatically chosen as a candidate gene. The quadruple mutant aux1 lax1 lax2 lax3 and the single mutants, except lax1, presented an enhanced asymmetry in venation patterning. Additionally, the xylem vasculature of the lax2 mutant and the HaHB4 -expressing plants differed from the WT vasculature, including increased xylem length and number of xylem cell rows. Complementation of the lax2 mutant with the LAX2 gene restored both lateral-vein symmetry and xylem/stem area ratio in the stem, showing that auxin homeostasis is required to achieve normal vascular development. Interestingly, soybean plants ectopically expressing HaHB4 also showed an increased asymmetry in the venation patterning, accompanied by the repression of several GmLAX genes. Conclusions: Auxin influx carriers have a significant role in leaf venation pattering in leaves and, in particular, LAX2 is required for normal xylem development, probablt controlling auxin homeostasis.

Environmental enrichment attenuates the age-related decline in the mRNA expression of steroidogenic enzymes and reduces the methylation state of the steroid 5α-reductase type 1 gene in the rat hippocampus.

We analyzed the effects of aging and environmental enrichment on the mRNA expression and DNA methylation state of steroidogenic enzymes in the hippocampus. The effects of aging were evaluated by comparing young adult (90-day-old) and middle-aged (450-day-old) female Wistar rats. To elucidate the effects of environmental enrichment, a subgroup of middle-aged rats exposed to sensory and social stimulation for 105 days was compared to rats housed under standard laboratory conditions. Aging decreased the transcription of neurosteroidogenic-related genes and increased the promoter methylation state of cytochrome P450 side chain cleavage, 3α-hydroxysteroid dehydrogenase (3α-HSD) and 5α-reductase-1. Exposure of middle-aged rats to environmental enrichment increased mRNA levels of 5α-reductase-1, 3α-HSD and cytochrome P450 17α-hydroxylase/c17,20-lyase and decreased the methylation state of the 5α-reductase-1 gene. Thus, sensory and social stimulation attenuate the age-related decline in the mRNA expression of hippocampal steroidogenic enzymes. Epigenetic mechanisms associated with differential promoter methylation could be involved.

Long-term ovariectomy increases BDNF gene methylation status in mouse hippocampus.

Estradiol (E) has been suggested to have a neuroprotective effect in young animals but has neutral or harmful effects when it is administered to aged animals. In the present study, we determined whether the post-ovariectomy (post-OVX) timeframe elapsed before the initiation of chronic E treatment is critical for the estrogenic induction of neurotrophins (brain-derived neurotrophic factor, BDNF, and synaptophysin, SYN) in the rodent hippocampus. Adult mice were OVX and, a short period (short-term E (STE) animals) or a long period (long-term E (LTE) animals) after the OVX, were daily treated with E. Control animals were treated with sesame oil (short-term control (STC) and long-term control (LTC) animals). Protein expression was determined using an immunohistochemical approach. Transcriptional activity in the hippocampus of individual BDNF promoters was assessed by real-time quantitative RT-PCR, and the methylation levels of regulatory regions were analyzed by methylation-specific PCR and combined bisulfite restriction analysis. STE animals showed increased BDNF and SYN protein expression and a higher activity of BDNF II, IV, and V promoters. In contrast, LTE animals did not show E induction of neurotrophins. In these animals, the methylation levels of regulatory sequences of the BDNF were higher than in the STE animals in a CpG island of promoter V and in the CRE regulatory site located in promoter IV. With this experiment, we determined that a prolonged period of hypoestrogenicity disrupts the E-induction of neurotrophins, and we postulated that DNA methylation is one of the epigenetic mechanisms that could explain the E-insensitivity of the BDNF after a long period post-OVX.