Contribution of atmospheric nitrate to stream-water nitrate in Japanese coniferous forests revealed by the oxygen isotope ratio of nitrate.

Evaluation of the openness of the nitrogen (N) cycle in forest ecosystems is important in efforts to improve forest management because the N supply often limits primary production. The use of the oxygen isotope ratio (delta(18)O) of nitrate is a promising approach to determine how effectively atmospheric nitrate can be retained in a forest ecosystem. We investigated the delta(18)O of nitrate in stream water in order to estimate the contribution of atmospheric NO(3) (-) in stream-water NO(3) (-) (f(atm)) from 26 watersheds with different stand ages (1-87 years) in Japan. The stream-water nitrate concentrations were high in young forests whereas, in contrast, old forests discharged low-nitrate stream water. These results implied a low f(atm) and a closed N cycle in older forests. However, the delta(18)O values of nitrate in stream water revealed that f(atm) values were higher in older forests than in younger forests. These results indicated that even in old forests, where the discharged N loss was small, atmospheric nitrate was not retained effectively. The steep slopes of the studied watersheds (>40 degrees ) which hinder the capturing of atmospheric nitrate by plants and microbes might be responsible for the inefficient utilization of atmospheric nitrate. Moreover, the unprocessed fraction of atmospheric nitrate in the stream-water nitrate in the forest (f(unprocessed)) was high in the young forest (78%), although f(unprocessed) was stable and low for other forests (5-13%). This high f(unprocessed) of the young forest indicated that the young forest retained neither atmospheric NO(3) (-) nor soil NO(3) (-) effectively, engendering high stream-water NO(3) (-) concentrations.

Noradrenergic modulation of gonadotrophin-inhibitory hormone gene expression in the brain of Japanese quail.

Gonadotrophin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that inhibits gonadotrophin synthesis and release in birds and mammals. In Japanese quail, GnIH neurones express the noradrenergic receptor and receive noradrenergic innervation. Treatment with noradrenaline (NA) stimulates GnIH release from diencephalic tissue blocks in vitro. However, the effects of NA on hypothalamic GnIH gene expression have not been determined. We investigated noradrenergic regulation of GnIH gene expression in the brain of male quail using the selective noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4). We first showed that DSP-4 reduced the number of noradrenergic (dopamine-ß-hydroxylase immunoreactive) cells in the locus coeruleus (LoC) and specifically lowered the NA concentration in the hypothalamus of male quail. Other monoamines, such as dopamine and serotonin, were not affected by drug treatment. DSP-4 did not decrease the numbers of noradrenergic cells of the lateral tegmental cell group, nor the plasma NA concentration. Decreased hypothalamic NA levels after DSP-4 treatment did not change GnIH gene expression in the brains of quail during their interaction with conspecifics. On the other hand, GnIH gene expression increased in the brains of quail socially isolated for 1 hour after DSP-4 treatment. These results suggest that some noradrenergic neurones have inhibitory effects on GnIH gene expression of the hypothalamus in solitary quail.

A study of spontaneous mutation rates at ten loci detectable by starch gel electrophoresis in Drosophila melanogaster.

Spontaneous mutation rates at ten allozyme loci on chromosomes II and III of Drosophila melanogaster were studied. Over the three and a half years study, one alpha-GPD mutation and two different IDH mutations were obtained. The alpha-GPD mutation was inherited in the Mendelian fashion, as expected. The two IDH mutations were peculiar in that the band of new types appeared only in females. In males, only the original bands were stained, and the positions where mutant alleles' bands should be present were blank. Both IDH mutant homozygotes appeared as null allele homozygotes, while in females clear-cut single bands were present.-The rates of spontaneous mutation varied greatly. Eight loci studied (MDH, ADH, EST-6, APH, EST-C, ODH, XDH, AO) did not give any germ-line mutation. The average germ-line mutation rate over all ten loci was estimated at 4.5 x 10(-6). This rate is considerably smaller than that for sex-linked recessive visible mutations (Muller, Valencia and Valencia 1950), but it is somewhat less than autosomal recessive visible mutations (Glass and Ritterhoff 1956).

Linkage disequilibrium in natural populations of Drosophila melanogaster.

Two large, stable populations (Texas and Japan) of Drosophila melanogaster were surveyed at 21 allozyme loci on the second and third chromosomes and for chromosomal gene arrangements on those two chromosomes. Over 220 independent gametes were sampled from each population. The types and frequencies of the surveyed genetic variation are similar to those observed previously and suggest only slight differentiation among geographically distant populations. Linkage disequilibrium among linked allozymes loci is only slightly, if at all, detectable with these sample sizes. Linkage disequilibrium between linked inversions and allozymes loci is common especially when located in the same arm. These disequilibria appear to be in the same direction for most comparisons in the two population samples. This result is interpreted as evidence of similar selective environments (ecological and genetic) in the two populations. It is also noted that the direction of these linkage disequilibria appears to be oriented with respect to the gene frequencies at the component loci.

Association of Chromosome and Enzyme Polymorphisms in Natural and Cage Populations of DROSOPHILA MELANOGASTER.

The frequencies of a polymorphic inversion, In(2L)t, and of Adh and alphaGpdh alleles were analyzed in three natural populations of Drosophila melanogaster from Japan. Significant positive correlations between the frequencies of In(2L)t and Adh(S) or alphaGpdh(F) were detected due to tight linkage. An analysis of correlation with latitude showed that the negative cline of Adh(S) frequency could be explained entirely by its linkage with In(2L)t; the frequency of Adh(S) on the standard chromosome did not show a latitudinal cline. To the contrary, the cline of alphaGpdh(F) frequency itself was positive, and its linkage with In(2L)t makes the positive cline unclear. These results suggest that the two allozymes themselves respond to latitudinal natural selection in different ways. When these populations were transferred to laboratory cages and maintained for a long time, they lost the chromosomal polymorphism but retained stable enzyme polymorphisms, although allele frequencies in the cage were not the same as in nature. The frequencies of Adh and alphaGpdh alleles were close to those in earlier cage populations of the same geographical origin.

Retrotransposon-induced ectopic expression of cut causes the Om(1A) mutant in Drosophila ananassae.

Optic morphology (Om) mutations in Drosophila ananassae map to at least 22 loci scattered throughout the genome. They are semidominant, neomorphic, nonpleiotropic, and are associated with the insertion of a retrotransposon, tom. The Om(1A) gene, which is cytogenetically linked to the cut locus, was cloned using a DNA fragment of the cut locus of Drosophila melanogaster as a probe. Three of the eight alleles of Om(1A) examined have insertion of the tom element within a putative cut region. The gamma-ray-induced revertants of Om(1A) are accompanied with cut lethal mutations and rearrangements within the cut coding region. In the eye imaginal discs of the Om(1A) mutants, differentiation of photoreceptor clusters is suppressed, abnormal cell death occurs in the center and the cut protein is expressed ectopically. D. melanogaster flies transformed with a chimeric cut gene under the control of a heat-inducible promoter show excessive cell death in the region anterior to the morphogenetic furrow, suppressed differentiation to photoreceptor clusters and defect in the imaginal eye morphology when subjected to temperature elevation. These findings suggest that the tom element inserted within the Om(1A) region induces ectopic cut expression in the eye imaginal discs, thus resulting in the Om(1A) mutant phenotype.

A site specific increase in recombination in Drosophila ananassae.

The e65 pi; bri ru stock of Drosophila ananassae produced an extremely high rate of recombination in males when made heterozygous with any one of the wild type stocks. We analyzed and characterized the genetic factors which caused this phenomenon. We show that the second chromosome of the e65 pi; bri ru stock carries an enhancer of male recombination. The enhancer, En(2)-ep, is located between Om(2C) and Arc. The enhancement of meiotic recombination both in males and females was also observed at the specific region between Om(2C) and Arc on 2L. The magnitude of increased recombination was 30-40 fold in males and 13-30 fold in females. The relation between the hotspot of recombination in both sexes and the enhancer of male recombination is discussed.

Identification, localisation and functional implication of 26RFa orthologue peptide in the brain of zebra finch (Taeniopygia guttata).

Several neuropeptides with the C-terminal Arg-Phe-NH(2) (RFa) sequence have been identified in the hypothalamus of a variety of vertebrates. The present study was conducted to isolate novel RFa peptides from the zebra finch brain. Peptides were isolated by immunoaffinity purification using an antibody that recognises avian RFa peptides. The isolated peptide consisted of 25 amino acids with RFa at its C-terminus. The sequence was SGTLGNLAEEINGYNRRKGGFTFRFa. Alignment of the peptide with vertebrate 26RFa has revealed that the identified peptide is the zebra finch 26RFa. We also cloned the precursor cDNA encoding this peptide. Synteny analysis of the gene showed a high conservation of this gene among vertebrates. In addition, we cloned the cDNA encoding a putative 26RFa receptor, G protein-coupled receptor 103 (GPR103) in the zebra finch brain. GPR103 cDNA encoded a 432 amino acid protein that has seven transmembrane domains. In situ hybridisation analysis in the brain showed that the expression of 26RFa mRNA is confined to the anterior-medial hypothalamic area, ventromedial nucleus of the hypothalamus and the lateral hypothalamic area, the brain regions that are involved in the regulation of feeding behaviour, whereas GPR103 mRNA is distributed throughout the brain in addition to the hypothalamic nuclei. When administered centrally in free-feeding male zebra finches, 26RFa increased food intake 24 h after injection without body mass change. Diencephalic GPR103 mRNA expression was up-regulated by fasting for 10 h. Our data suggest that the hypothalamic 26RFa-its receptor system plays an important role in the central control of food intake and energy homeostasis in the zebra finch.

Cytogenetic analysis of recombination in males of Drosophila ananassae.

Cytogenetic studies of recombination in males of Drosophila ananassae were carried out by examining F1 males derived from he mating of marker females, b se; bri ru of the BS stock, with males of two wild strans, TNG and L8. The male recombination values in both sections b-se (chromosome 2) and bri-ru (chromosome 3) are high in TNG F1 but extremely low in L8 F1. We demonstrate the presence of chiasmata in TNG F1 males at a frequency capable of accounting for the observed recombination values. A unique series of "iso-site aberrations" was also observed in TNG F1 males. Because of a parallelism in the distribution pattern between the chiasmata and the iso-site aberrations, we propose that recombination in males of D. ananassae is meiotic in origin and that the iso-site aberrations are related to chiasma formation.

Genetic analysis of the Om(2D) locus in Drosophila ananassae.

The Om(2D)63 mutants were mutagenized by gamma-ray irradiation and DEB feeding. A total of nine revertants were recovered and characterized; eight revertants were homozygous-lethal expressing no appreciable abnormality in cuticular pattern and central nervous system, and all failed to complement the lethality with each other. Two of the eight expressed embryonic lethality and were associated with cytologically detectable deletions including the putative Om(2D) locus, while four were associated with rearrangements in a region distal to the insertion sites of the tom elements. No rearrangement was detected in the remaining two by Southern blot analysis. One of the nine revertants was homozygous-viable with wild-type eyes and was associated with a reciprocal translocation with the break points at 48B in 2R (Om(2D) locus) and 96A in 3R. Based on these data, it is concluded that interaction between the region comprised of a single complementation group of the recessive lethal and the inserted tom elements seems to be responsible for the Om(2D) mutant phenotype. In addition, two induced dominant enhancers specific to Om(2D)63 were identified; both mapped on chromosome 2.

Cytological mapping of Om mutants of Drosophila ananassae.

Semidominant, optic morphology (Om) mutants in Drosophila ananassae have been genetically mapped to at least 25 loci throughout the genome (Hinton, 1984; 1988). Among them, four X-linked Om mutants were proved to be associated with the insertion of a transposable element, tom (Shrimpton et al., 1986; Tanda et al., 1988). In the present study, cytological mapping of autosomal Om mutants was carried out by in situ hybridization to polytene chromosomes using a cloned tom element as a probe. The cytological site for each autosomal Om mutant has been determined to a single band of the salivary gland chromosomes.

Molecular and histological characterizations of the Om(2D) mutants in Drosophila ananassae.

A series of transposon-induced optic morphology (Om) mutants found in a hypermutable marker stock of Drosophila ananassae provides a useful system for analyzing the molecular mechanism of eye morphogenesis. In the present study, one of the 25 Om loci so far reported, Om(2D), has been subjected to histological and molecular analyses as a first step toward understanding the role of Om genes in eye morphogenesis. Histological abnormalities observed during eye morphogenesis of the mutant, i.e. cell death within the eye-antennal discs of third instar larvae, and loss of the lamina, disorganized ommatidia and atrophied optic lobes in adults, were all comparable to those reported with various eye morphology mutants of D. melanogaster. Approximately 25 kb of genomic DNA including the Om (2D) locus was cloned by tom tagging. Southern blot and cloning analyses of two alleles of the Om (2D) locus revealed that insertions of the tom element occurred at three sites within 359 bp; two tandemly arrayed toms sharing one long terminal repeat at the junction and an internally deleted tom were present 359 bp apart from each other in Om (2D) 63, while a single tom in reverse orientation was present within the 359 bp in Om (2D) 10a. Host DNA sequences at the three insertion sites were TATAT or AATAT, and ATAT was duplicated upon the tom insertion.(ABSTRACT TRUNCATED AT 250 WORDS)

Retrovirus-like features and site specific insertions of a transposable element, tom, in Drosophila ananassae.

The tom element, putatively associated with optic morphology (Om) mutations in Drosophila ananassae, was identified as a retrovirus-like transposable element. The tom element was found to terminate with 475 (or 474) base pair direct repeats which are identical in sequence to each other. Southern blot and heteroduplex analyses showed the tom element to have high homology to 297 and 17.6, two retrotransposons found in D. melanogaster. As in the cases of 297 and 17.6, tom includes nucleotide sequences coding for a presumptive protease and reverse transcriptase, similar in amino acid sequence to those of the Moloney murine leukaemia virus. At the tom insertion site of the sn9g locus, a host DNA sequence (T)ATAT was found to be duplicated on each side of the tom insertion and all other tom elements examined were also flanked by (T)ATAT. In each of six cases, the 5' flanking host sequence was TATAT. These results indicate that the target sequence of the tom element may be TATAT and that the entire region or a part of this sequence was duplicated on insertion of the tom element.