Evidence for presence of kynurenine in lung and brain of neonate hamsters

Summary Using immunocytochemical techniques, we report here direct evidence of kynurenine (Kyn) presence and localization in the lung and brain. Kyn is a metabolite of tryptophan and 5-hydroxytryptophan, produced by indoleamine 2, 3-dioxygenase (IDO). Whereas IDO has been quantitated in tissues from lung, brain, and other organs, Kyn has only been identified in brain (by HPLC), and its specific localization has not been determined.We reacted alternate serial paraffin sections with anti-sera raised in rabbits against a l-Kyn-albumin conjugate, and with anti-5HT (serotonin, 5-hydroxytryptamine), using the PAP method. Kyn-like immunoreactivity in the lung was specifically localized to cells of the bronchiolar epithelium resembling basal cells. Taller epithelial cells in the bronchi and dorsal trachea were likewise positive whereas neuroepithelial bodies were negative. Immunoreactivity in the brain was typically localized to cells localized in the ependyma of the walls of all ventricles, and to nerve fibers. The cellular Kyn-like reactivity was totally separate from that of anti-5HT, the latter uniquely staining argyrophil lung neuroendocrine cells and raphae neurons of the brain. Our findings suggest a route of tryptophan metabolism in the lung and brain alternate to the common pathway leading to 5-hydroxyindoleacetic acid via 5-HT. This route is of physiologic and pathologic significance as many metabolites are pharmacologically active.Supported by the College of Agriculture and Life Sciences, University of Wisconsin-Madison and the Council for Tobacco Research USA, Inc. Grant #1437     

Imprinting of the Polycomb Group Gene MEDEA Serves as a Ploidy Sensor in Arabidopsis

Balanced maternal and paternal genome contributions are a requirement for successful seed development. Unbalanced contributions often cause seed abortion, a phenomenon that has been termed “triploid block.” Misregulation of imprinted regulatory genes has been proposed to be the underlying cause for abnormalities in growth and structure of the endosperm in seeds with deviating parental contributions. We identified a mutant forming unreduced pollen that enabled us to investigate direct effects of unbalanced parental genome contributions on seed development and to reveal the underlying molecular mechanism of dosage sensitivity. We provide evidence that parent-of-origin–specific expression of the Polycomb group (PcG) gene MEDEA is causally responsible for seed developmental aberrations in Arabidopsis seeds with increased paternal genome contributions. We propose that imprinted expression of PcG genes is an evolutionary conserved mechanism to balance parental genome contributions in embryo nourishing tissues.     

A dynamic DUO of regulatory proteins coordinates gamete specification and germ cell mitosis in the angiosperm male germline

The production of two functional sperm cells within each male gametophyte is essential for double fertilization in flowering plants and involves a single mitotic division of the male germ cell and cell specification to produce functional gametes. Several proteins that are important regulators of male germ cell division have been identified as well as the R2R3 MYB protein DUO1 that has a dual role in cell division and cell specification. We recently identified a novel regulatory protein DUO3, that has overlapping roles with DUO1 in cell division and specification and shows similarity to GON4 related cell lineage regulators in animals. DUO3 also has important roles outside the germline and is required for embryo patterning and meristem function. We outline the regulatory roles of DUO3 in male germline development and its possible mechanisms of action as a lineage regulator in current models that link germ cell cycle control and gamete specification.Key words: DUO3, male germline development, cell cycle, cell specification, Arabidopsis, pollen, GON4-LThe two sperm cells required for double fertilization in flowering plants are produced after an asymmetric division of the haploid microspore produces a large vegetative cell and a smaller germ cell, thereby establishing the male germline (reviewed in ref. 1; Fig. 1A). The germ cell is engulfed within the vegetative cell cytoplasm where it divides to produce the two sperm cells. The germ cell also goes through a process of specification, with ∼6,000 genes expressed in sperm cells,² many of which show specific or enhanced expression in the male germline and/or are essential for fertilization.^2–4 Since 2005 a number of proteins with important regulatory roles in either germ cell division^5–9 or both germ cell division and specification^10–12 have been described, enabling the formulation of basic models for the regulation of male germline development.^12,13 In our recent publication¹⁴ we identify a novel regulatory protein, DUO POLLEN3 (DUO3) that has essential roles in germ cell division and specification, as well as vital sporophytic functions. Here we present the role of DUO3 in an emerging model for the regulation of male germline development in Arabidopsis (Fig. 1B) and briefly discuss the wider role and possible mechanism of DUO3 function.Open in a separate windowFigure 1Overview of male gametophyte development in arabidopsis (a) and model of germ cell cycle progression and specification in the male germline (B). (A) Schematic of the distinct morphological stages of male gametophyte development in arabidopsis. Diploid pollen mother cells undergo meiotic division to produce a tetrad of haploid microspores. the released microspores undergo a highly asymmetric division to produce a bicellular pollen grain with a small germ cell engulfed within the cytoplasm of a large vegetative cell. Whilst the vegetative cell exits the cell cycle, the germ cell undergoes a further mitotic division to produce twin sperm cells. (B) a schematic model integrating the control of cell proliferation and sperm cell specification in male germline development of arabidopsis. after microspore division, the cell cycle inhibitors KrP6 and KrP7 are present in the newly formed germ cell. transient expression of FBL17 leads to the degradation of these KRPs, allowing CDKA/CYCD to phosphorylate RBR, thereby relieving RBR-mediated repression of the E2F/DP pathway and progression of the germ cell through S-phase. Gamete specification begins shortly after germ cell division, where the co-expression of DUO1 and DUO3 in the germ cell leads to the activation of common and distinct germline differentiation genes. Once S-phase is complete, the DuO1-dependent activation of the G₂/m phase regulator CYCB1;1 promotes germ cell cycle progression and entry into mitosis. In parallel, DUO3 also controls G₂/m transition, by an unknown mechanism that acts independently of cYcB1;1 expression. DUO1 and DUO3 therefore integrate germline differentiation with cell cycle progression. Ultimately, the cooperation of these parallel pathways results in a pair of fully differentiated sperm cells equipped with a complement of essential germline factors such as GcS1 that are required for successful gamete fusion.