The Phylogenetic Relationships of the Members of the DROSOPHILA ROBUSTA Group

The phylogenetic relationships among the species of the D. robusta group were investigated by the analysis of chromosomal differences. Six of the ten known members of the D. robusta group were available for the study: D. colorata and D. robusta from the United States, and D. sordidula, D. pseudosordidula, D. lacertosa, and D. moriwakii from Japan. Analysis of the metaphase chromosomes from larval ganglion cells suggests that D. moriwakii and D. colorata, with rod-shaped X-chromosomes, are the more ancestral species, while D. sordidula, D. pseudosordidula, D. robusta, and D. lacertosa, with V-shaped X-chromosomes, are derived. The ancestral position of D. colorata and D. moriwakii is further strengthened by the fact that these are the two species in the D. robusta group that are cytologically closest to D. nigromelanica of the related D. melanica group. Of the four derived species, D. sordidula was found to be the closest to the ancestral species. The phylogeny based on the analysis of the gene sequences in the homologous chromosomes agreed with that indicated by the metaphase chromosomes. Since all attempts to obtain hybrids were unsuccessful except for the cross involving D. moriwakii females and D. colorata males, photographic maps of the salivary chromosomes were used to determine homology between the chromosomes of the different species. Evidence is presented to indicate that the D. robusta group originated in Asia (Japan), and that there were two migrations to the New World, the first leading to D. robusta, and the second to D. colorata. It is suggested that the route of migrations was across the Bering Land Bridge, and further, that the migrations occurred during the period from late Oligocene to middle Miocene, 20-25 million years ago.     

Arylamine N-acetyltransferase and arylalkylamine N-acetyltransferase in the mammalian pineal gland

Amine N-acetylation in the pineal gland is of special importance because it is the first step in the synthesis of melatonin from serotonin. In the present study the N-acetylation of arylamines and arylalkylamines by homogenates of rat and sheep pineal glands was investigated. The arylamines studied were p-phenetidine and aniline; the arylalkylamines studied were tryptamine, serotonin, 5-methoxytryptamine, 6-fluorotryptamine, and phenylethylamine. These amines were acetylated by pineal homogenates of both species, although marked interspecies differences in apparent Km and Vmax values were found. A series of observations in both species indicate that aromatic amine N-acetylation is catalyzed by two distinct enzymes; one preferentially acetylates arylamines and the other preferentially acetylates arylalkylamines. First, isoproterenol treatment of the rat increased arylalkylamine N-acetylation 100-fold without increasing arylamine N-acetylation. Second, cycloheximide treatment in sheep reduced arylalkylamine N-acetylation at night to one-tenth control values, without altering arylamine N-acetylation. Third, arylamine N-acetyltransferase and arylalkylamine N-acetyltransferase inactivated at different rates at 4 degrees C. Fourth, the two enzymes were resolved by size exclusion chromatography. These results clearly establish that the pineal gland contains an arylamine N-acetyltransferase and a second, independently regulated arylalkylamine N-acetyltransferase which appears to be primarily responsible for the physiological conversion of serotonin to melatonin via the intermediate N-acetylserotonin.     

Compromised base excision repair pathway in Mycobacterium tuberculosis imparts superior adaptability in the host

Tuberculosis caused by Mycobacterium tuberculosis (Mtb) is a significant public health concern, exacerbated by the emergence of drug-resistant TB. To combat the host’s dynamic environment, Mtb encodes multiple DNA repair enzymes that play a critical role in maintaining genomic integrity. Mtb possesses a GC-rich genome, rendering it highly susceptible to cytosine deaminations, resulting in the occurrence of uracils in the DNA. UDGs encoded by ung and udgB initiate the repair; hence we investigated the biological impact of deleting UDGs in the adaptation of pathogen. We generated gene replacement mutants of uracil DNA glycosylases, individually (RvΔung, RvΔudgB) or together (RvΔdKO). The double KO mutant, RvΔdKO exhibited remarkably higher spontaneous mutation rate, in the presence of antibiotics. Interestingly, RvΔdKO showed higher survival rates in guinea pigs and accumulated large number of SNPs as revealed by whole-genome sequence analysis. Competition assays revealed the superior fitness of RvΔdKO over Rv, both in ex vivo and in vivo conditions. We propose that compromised DNA repair results in the accumulation of mutations, and a subset of these drives adaptation in the host. Importantly, this property allowed us to utilize RvΔdKO for the facile identification of drug targets.