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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Article
  • Peer Reviewed
The Proceedings of the International Plant Nutrition Colloquium XVI (2009)

Nitrate uptake characteristics and ammonium effects were compared between upland rice (Brazilian upland rice) and paddy rice (Wuyujing 3 and Yangdao 6) through the glass microelectrode technique and the concentration gradient method of uptake kinetics. Results indicated that nitrate uptake by rice seedlings and ammonium effects were related to transmembrane potential difference, and upland rice and paddy rice presented obviously different responses. Nitrate induced a rapid depolarization and then a slow repolarization of transmembrane potential in root epidermal cells, and even hyperpolarization was observed when nitrate concentration was low. Resting transmembrane potential of epidermal cells in Brazilian upland rice roots was lower and its response to NO3- was bigger than that of two paddy rice species. Depolarization of membrane potential was amplified when ammonium was simultaneously added with nitrate into the measure medium, but repolarization was reduced, even disappeared. Brazilian upland rice seedlings had high Vmax of nitrate uptake and low Km, furthermore, Vmax and Km were little affected by ammonium, but Vmax of Wuyujing 3 was reduced significantly. Therefore, inhibition of ammonium to nitrate uptake possibly due to decrease of membrane potential and influence of nitrate transporters. Moreover, inhibition of NH4+ differed obviously between upland rice and paddy rice.

    Cover page: Ammonium Effects on Nitrate Uptake by Roots of Upland and Paddy Rice Seedlings Related to Transmembrane Potential Differences
    • Article
    • Peer Reviewed
    The Proceedings of the International Plant Nutrition Colloquium XVI (2009)

    Most of plants uptook NO3--N faster at the low pH 4.0 than at pH 6.0 and uptook NH4+-N slower, but few experimental plants showed different tendency. The exceptions probably due to excessive nitrate outflux of some maize and wheat varieties (Suyu 19. Zhendan958 and Yangmai12) at low pH. Some other experimental plants (Huaidao 8. Nongda108 and Yangmai12) even show no obvious NH4+ toxic symptoms at pH 4.0. The effect of low pH on uptake rate of NH4+-N and NO3--N varied with plant species, varieties, and the difference increased with the growth age of seedlings.

      Cover page: Effect of low pH on Uptake of Inorganic Nitrogen by Different Plant Seedlings
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2021)
      Current treatments for antibody-mediated autoimmunity are associated with lack of specificity, leading to immunosuppressive effects. To overcome this limitation, we have developed a class of antibody-based therapeutics for the treatment of autoimmunity involving antibodies that recognize the autoantigen, myelin oligodendrocyte glycoprotein (MOG). These agents ("Seldegs," for selective degradation) selectively eliminate antigen (MOG)-specific antibodies without affecting the levels of antibodies of other specificities. Seldeg treatment of mice during antibody-mediated exacerbation of experimental autoimmune encephalomyelitis by patient-derived MOG-specific antibodies results in disease amelioration. Consistent with their therapeutic effects, Seldegs deliver their targeted antibodies to Kupffer and liver sinusoidal endothelial cells that are known to have tolerogenic effects. Our results show that Seldegs can ameliorate disease mediated by MOG-specific antibodies and indicate that this approach also has the potential to treat other autoimmune diseases where the specific clearance of antibodies is required.
        Cover page: Selective Depletion of Antigen-Specific Antibodies for the Treatment of Demyelinating Disease
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2022)
        Sertoli cells (SCs) support and nourish germ cells (GCs) through their crosstalk during spermatogenesis. However, the underlying epigenetic mechanism that ensures SCs' functions in this process remains unclear. Here, we report that UHRF1, a critical epigenetic regulator, is mainly expressed in human and mouse pre-mature SCs, and is essential for establishing Sertoli-Germ cell crosstalk. SC-specific UHRF1 knockout mice exhibit complete sterility with Sertoli cell (SC) proliferation and differentiation aberrance, blood-testis barrier (BTB) disruption, and immature germ cell (GC) sloughing. RNA sequencing and Whole Genome Bisulfite Sequencing (WGBS) revealed that many extracellular matrix (ECM)-related genes (e.g., Timp1, Trf, and Spp1) appeared upregulated with the DNA hypomethylation status in UHRF1-deficient SCs. Strikingly, overexpression of Timp1, Trf, and Spp1 in SCs in vitro and in vivo could phenocopy the SC-specific UHRF1-deficient mice. Our data demonstrated that UHRF1 regulates the transcriptional program of ECM-related genes in SCs and establishes SC-GC crosstalk.
          Cover page: UHRF1 establishes crosstalk between somatic and germ cells in male reproduction
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2023)
          Pachytene piRNA biogenesis is a hallmark of the germline, distinct from another wave of pre-pachytene piRNA biogenesis with regard to the lack of a secondary amplification process known as the Ping-pong cycle. However, the underlying molecular mechanism and the venue for the suppression of the Ping-pong cycle remain elusive. Here, we showed that a testis-specific protein, ADAD2, interacts with a TDRD family member protein RNF17 and is associated with P-bodies. Importantly, ADAD2 directs RNF17 to repress Ping-pong activity in pachytene piRNA biogenesis. The P-body localization of RNF17 requires the intrinsically disordered domain of ADAD2. Deletion of Adad2 or Rnf17 causes the mislocalization of each other and subsequent Ping-pong activity derepression, secondary piRNAs overproduced, and disruption of P-body integrity at the meiotic stage, thereby leading to spermatogenesis arrested at the round spermatid stage. Collectively, by identifying the ADAD2-dependent mechanism, our study reveals a novel function of P-bodies in suppressing Ping-pong activity in pachytene piRNA biogenesis.
            Cover page: ADAD2 interacts with RNF17 in P-bodies to repress the Ping-pong cycle in pachytene piRNA biogenesis
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2019)
            DNA methylation, repressive histone marks, and PIWI-interacting RNA (piRNA) are essential for the control of retrotransposon silencing in the mammalian germline. However, it remains unknown how these repressive epigenetic pathways crosstalk to ensure retrotransposon silencing in the male germline. Here, we show that UHRF1 is responsible for retrotransposon silencing and cooperates with repressive epigenetic pathways in male germ cells. Conditional loss of UHRF1 in postnatal germ cells causes DNA hypomethylation, upregulation of retrotransposons, the activation of a DNA damage response, and switches in the global chromatin status, leading to complete male sterility. Furthermore, we show that UHRF1 interacts with PRMT5, an arginine methyltransferase, to regulate the repressive histone arginine modifications (H4R3me2s and H3R2me2s), and cooperates with the PIWI pathway during spermatogenesis. Collectively, UHRF1 regulates retrotransposon silencing in male germ cells and provides a molecular link between DNA methylation, histone modification, and the PIWI pathway in the germline.
              Cover page: UHRF1 suppresses retrotransposons and cooperates with PRMT5 and PIWI proteins in male germ cells
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