Systematic Screening of Drosophila Deficiency Mutations for Embryonic Phenotypes and Orphan Receptor Ligands

This paper defines a collection of Drosophila deletion mutations (deficiencies) that can be systematically screened for embryonic phenotypes, orphan receptor ligands, and genes affecting protein localization. It reports the results of deficiency screens we have conducted that have revealed new axon guidance phenotypes in the central nervous system and neuromuscular system and permitted a quantitative assessment of the number of potential genes involved in regulating guidance of specific motor axon branches. Deficiency “kits” that cover the genome with a minimum number of lines have been established to facilitate gene mapping. These kits cannot be systematically analyzed for phenotypes, however, since embryos homozygous for many deficiencies in these kits fail to develop due to the loss of key gene products encoded within the deficiency. To create new kits that can be screened for phenotype, we have examined the development of the nervous system in embryos homozygous for more than 700 distinct deficiency mutations. A kit of ∼400 deficiency lines for which homozygotes have a recognizable nervous system and intact body walls encompasses >80% of the genome. Here we show examples of screens of this kit for orphan receptor ligands and neuronal antigen expression. It can also be used to find genes involved in expression, patterning, and subcellular localization of any protein that can be visualized by antibody staining. A subset kit of 233 deficiency lines, for which homozygotes develop relatively normally to late stage 16, covers ∼50% of the genome. We have screened it for axon guidance phenotypes, and we present examples of new phenotypes we have identified. The subset kit can be used to screen for phenotypes affecting all embryonic organs. In the future, these deficiency kits will allow Drosophila researchers to rapidly and efficiently execute genome-wide anatomical screens that require examination of individual embryos at high magnification.     

Acid-catalyzed hydration of reduced nicotinamide adenine dinucleotide and its analogues.

The rate of the primary acid modification reaction of 1,4-dihydronicotinamide adenine dinucleotide (NADH) and 1,4-dihydro-3-acetylpyridine adenine dinucleotide (APADH) and their analogues has been studied over a wide pH range (pH 1-7) with a variety of general acid catalysts. The rate depends on [H+] at moderate pH and becomes independent of [H+] at low pH. This behavior is attributed to substrate protonation at the carbonyl group (pK of NADH = 0.6). The reaction is general acid catalyzed; large solvent deuterium isotope effects are observed for the general acid and lyonium ion terms. Most buffers cause a linear rate increase with increasing buffer concentration, but certain buffers cause a hyperbolic rate increase. The nonlinear buffer effects are due to complexation of the buffer with the substrate, rather than to a change in rate-limiting step. The rate-limiting step is a proton transfer from the general acid species to the C5 position of the substrate. Anomerization is not a necessary first step in the case of the primary acid modification reaction of beta-NADH, in which beta to alpha anomerization takes place.     

Wiring diagrams of MAPK regulation by MEKK1, 2, and 3.

Mitogen-activated protein kinase (MAPK) pathways are activated by a plethora of stimuli. The literature is filled with papers describing the activation of different MAPKs by almost any stimulus or insult imaginable to cells. In this review, we use signal transduction wiring diagrams to illustrate putative upstream regulators for the MAPK kinase kinases, MEKK1, 2, and 3. Targeted gene disruption of MEKK1, 2, or 3 defined phenotypes for each MEKK associated with loss of specific MAPK regulation. Genetic analysis of MEKK function clearly defines specific components of the wiring diagram that require MEKK1, 2, or 3 for physiological responses. We propose that signal transduction network wiring diagrams are valuable tools for hypothesis building and filtering physiologically relevant phenotypic responses from less connected protein relations in the regulation of MAPK pathways.     

Effect of elevating serum lipids on luteinizing hormone response to gonadotrophin releasing hormone challenge in energy-deficient anestrous heifers

A study was conducted to evaluate the effect of feeding a bypass fat on luteinizing hormone (LH) response to gonadotrophin releasing hormone (GnRH) in noncyclic Holstein heifers. Twelve cyclic Holstein heifers were fed a complete diet at 40% net energy for maintenance (NE(m)) until cessation of ovarian activity. Based on weights and condition scores, heifers were assigned to either a control or treatment diet containing 0.45 kg bypass fat and fed at an energy level of 85% NE(m). Diet adjustments were made following weekly weighings. GnRH challenges were conducted at four periods: prior to initial energy deprivation, at termination of 40% NE(m) feeding, and twice more at 21-d intervals after 85% NE(m) feeding began. Blood was sampled via a jugular catheter every 15 min for 5 h, and GnRH was injected after the fourth sample. None of the heifers exhibited estrous activity after the initial energy deprivation. Heifers on the bypass fat diet continued to lose weight during the treatment period, while the control heifers gained a slight amount of weight. Baseline and peak concentrations of LH were not significantly affected by time or diet. Time to GnRH-induced LH peak was longer (53 vs 130 min, P < 0.01) after 40% NE(m) and remained greater at all times thereafter. Serum lipid levels increased 82.5% among heifers being fed the bypass fat. Energy restriction had no effect on the magnitude of LH response to GnRH but did delay response time.     

In vitro regeneration of apomictic bluestem grasses

Explants from immature inflorescences of four genotypes of Old World bluestem grasses, (Bothriochloa spp.), produced callus tissue on Linsmaier and Skoog (RM) and 1/2 Murashige and Skoog (1/2 MS) media containing high levels of growth regulators. Callus masses were composed of two distinct tissue types, one a compact, white, embryogenic portion (E calli), the other soft, translucent, gelatinous and nonembryogenic (NE calli). When transferred to medium with a reduced level of 2,4-D, and/or supplemented with zeatin, E callus underwent further organization culminating in shoot production. Light and scanning electron microscopy confirmed the embryogenic pathway of differentiation. Genotype significantly affected callus induction frequency and the number of plants regenerated. The RM medium induced more explants to initiate callus compared to the 1/2 MS medium. Age of the inflorescence explant, as indicated by size, was critical for callus induction. Inflorescences with racemes 8 mm in length were superior to older ones. Five-hundred-twenty-two plantlets were regenerated and grown to maturity.     

Regulation of auxin transport in pea (Pisum sativum L.) by phenylacetic acid: effects on the components of transmembrane transport of indol-3yl-acetic acid

Phenylacetic acid (PAA), a naturally-occurring acidic plant growth substance, was readily taken up by pea (Pisum sativum L. cv. Alderman) stem segments from buffered external solutions by a pH-dependent, non-mediated diffusion. Net uptake from a 0.2 M solution at pH 4.5 proceeded at a constant rate for at least 60 min and, up to approx. 100 M, the rate of uptake was directly proportional to the external concentration of the compound. The net rate of uptake of PAA was not affected by the inclusion of indol-3yl-acetic acid (IAA) in the uptake medium (up to approx. 30 M) and, unlike the net uptake of IAA, was not stimulated by N-1-naphthylphthalamic acid (NPA) or 2,3,5-triiodobenzoic acid. At an external concentration of 0.2 M and pH 4.5, the net rate of uptake of PAA was about twice that of IAA. It was concluded that the uptake of PAA did not involve the participation of carriers and that PAA was not a transported substrate for the carriers involved in the uptake and polar transport of IAA. Nevertheless, the inclusion of 3–100 M unlabelled PAA in the external medium greatly stimulated the uptake by pea stem segments of [1-¹⁴C]IAA (external concentration 0.2 M). It was concluded that whilst PAA was not a transported substrate for the NPA-sensitive IAA efflux carrier, it interacted with this carrier to inhibit IAA efflux from cells. Over the concentration range 3–100 M, PAA progressively reduced the stimulatory effect of NPA on IAA uptake, indicating that PAA also inhibited carrier-mediated uptake of IAA. The consequences of these observations for the regulation of polar auxin transport are discussed.Abbreviations IAA indol-3yl-acetic acid - DMO 5,5-dimethyloxazolidine-2,4-dione - NPA N-1-naphthylphthalamic acid - PAA phenylacetic acid - TIBA 2,3,5-triiodobenzoic acid     

Control of wild carrot somatic embryo development by antioxidants : a probable mode of action of 2,4-dichlorophenoxyacetic Acid

As we previously reported for glutathione (GSH), both ascorbic acid (AA) and vitamin E were observed to suppress wild carrot (Daucus carota L.) somatic embryogenesis with little concomitant effect on biomass. Endogenous concentrations of AA were lower during embryo development than during cell proliferation, exhibiting a temporal pattern nearly identical to that of GSH. GSSG (oxidized GSH) reductase was found to be considerably more active in proliferating than in developing cultures, whereas no difference was evident in the case of dehydroascorbate (DHA) reductase. Both GSH and AA concentrations in these cells are governed by 2,4-D. These results show that redox status is a strong determinant of proliferative versus developmental growth and indicate that the mode of action of 2,4-D in this system may be explained at least in part by its influence on endogenous antioxidant levels.