Localization of melanin synthesis within the pigment cell: Determination by a combination of electron microscopic autoradiography and topographic planimetry

Summary Localization of melanin synthesis within the pigment cells of the Cloudman S-91 mouse melanoma was determined by means of a combination of high resolution autoradiography and topographic planimetry. Initial melanin biosynthesis occurred predominantly in the endoplasmic reticulum and associated ribonucleoprotein particles of the melanocytes. By measuring a number of cell organelles and employing the index of relative specific localization it could be shown that the nucleus and mitochondria are of little or no importance in the process of melanogenesis.This investigation has been supported by the following research grants: CA 06548 CB, NIH, PHS and an Institutional Grant from the American Cancer Society (to H. M. H.); CA-05887, NIH, PHS (to A. S. Z.); M-00388 and NB-00782, NIH, PHS (to J. F. H.). One of us (H. M. H.) holds a Research Cancer Development Award (5-K 3-GM-2634) of the National Institute of General Medical Sciences, Public Health Service.We are grateful to Mr. Ronald Abler for his help with the topographic measurements; to Dr. Erhard Haus for help and advice; to Mr. J. Thornby and Mr. A. P. Basu for assistance with the statistical aspects of this study; and to Mrs. Lenore Mottaz, Miss Bernice Uittenbogaard, and Mrs. Judith Strong for careful technical assistance.     

Meiotic gene conversion and crossing over: their relationship to each other and to chromosome synapsis and segregation

The yeast mer1 mutant produces inviable spores and is defective in both meiotic recombination and chromosome pairing. A gene called MER2 partially suppresses the mer1 phenotype when present in high copy number. Both gene conversion and chromosome pairing are completely restored in mer1 strains overexpressing MER2; however, reciprocal crossing over and spore viability are not restored. The data presented are consistent with a model in which chromosome pairing is a direct consequence of a homology search mediated through gene conversion. Analysis of random viable spores indicates that the crossovers that occur in mer1 strains overexpressing MER2 are more effective in ensuring meiosis I disjunction than those that occur in mer1 strains. One interpretation of this result is that only those crossovers that occur in the context of the synaptonemal complex lead to the establishment of functional chiasmata. The MER2 gene product is essential for meiosis.     

Patterns of viral replication correlate with outcome in simian immunodeficiency virus (SIV)-infected macaques: effect of prior immunization with a trivalent SIV vaccine in modified vaccinia virus Ankara.

The dynamics of plasma viremia were explored in a group of 12 simian immunodeficiency virus (SIV)-infected rhesus macaques (Macaca mulatta) that had received prior immunization with either nonrecombinant or trivalent (gag-pol, env) SIV-recombinant vaccinia viruses. Three distinct patterns of viral replication observed during and following primary viremia accounted for significant differences in survival times. High-level primary plasma viremia with subsequently increasing viremia was associated with rapid progression to AIDS (n = 2). A high-level primary plasma virus load with a transient decline and subsequent progressive increase in viremia in the post-acute phase of infection was associated with progression to AIDS within a year (n = 6). Low levels of primary plasma viremia followed by sustained restriction of virus replication were associated with maintenance of normal lymphocyte subsets and intact lymphoid architecture (n = 4), reminiscent of the profile observed in human immunodeficiency virus type 1-infected long-term nonprogressors. Three of four macaques that showed this pattern had been immunized with an SIV recombinant derived from the attenuated vaccinia virus, modified vaccinia virus Ankara. These data link the dynamics and extent of virus replication to disease course and suggest that sustained suppression of virus promotes long-term, asymptomatic survival of SIV-infected macaques. These findings also suggest that vaccine modulation of host immunity may have profound beneficial effects on the subsequent disease course, even if sterilizing immunity is not achieved.     

Diversity and structure of hyphomicrobium populations in a sewage treatment plant and its adjacent receiving lake

Budding methylotrophic bacteria resembling Hyphomicrobium spp. were counted for 12 months in a German sewage treatment plant by most-probable-number (MPN) methods. Influent samples contained up to 2 x 10(sup4) cells ml(sup-1), activated sludge consistently contained 1 x 10(sup5) to 5 x 10(sup5) cells ml(sup-1), and the effluent contained 1 x 10(sup3) to 4 x 10(sup3) cells ml(sup-1). The receiving lake had only 2 to 12 cells ml(sup-1). Six morphological groups with different growth requirements could be observed among 1,199 pure cultures that had been isolated from MPN dilutions. With dot blot DNA hybridizations, 671 isolates were assigned to 30 hybridization groups (HGs) and 84 could not be classified. Only HG 22 hybridized with a known species, Hyphomicrobium facilis IFAM B-522. Fourteen HGs (HGs 8 to 20 and HG 22) were specific for the lake; most others occurred only in the treatment plant. HGs 1, 3, and 26 were found in the activated sludge tank throughout the year, and HGs 27 and 28 were found for most of the year. In summary, it was demonstrated that bacteria with nearly identical and specific morphologies and nutritional types showed a high level of genetic diversity, although they were isolated under the same conditions and from the same treatment plant or its receiving lake. A directional exchange of these genetically different populations was possible but less significant, as was shown by the establishment of distinct populations in specific stations.     

Analysis of partial sequences of genes coding for 16S rRNA of actinomycetes isolated from Casuarina equisetifolia nodules in Mexico.

Filamentous bacteria isolated from surface-sterilized nodules of Casuarina equisetifolia trees in México were capable of reducing acetylene, a diagnostic test for nitrogenase, but were unable to nodulate their host. Analysis of partial 16S rRNA gene sequences suggests that the Mexican isolates are not Frankia strains but members of a novel clade.     

Cloning,sequence analysis and expression of a cDNA encoding active phosphoenolpyruvate carboxylase of the C3 plant Solanum tuberosum

A cDNA coding for phosphoenolpyruvate carboxylase (PEPC) was isolated from a cDNA library from Solanum tuberosum and the sequence of the cDNA was determined. It was inserted into a bacterial expression vector and a PEPC^- Escherichia coli mutant could be complemented by the cDNA construct. A functional fusion protein could be synthesized in E. coli. The properties of this PEPC protein clearly resembled those of typical C3 plant enzymes.     

Immunocytochemical Quantification of Tyrosine Hydroxylase at a Cellular Level in the Mesencephalon of Control Subjects and Patients with Parkinson's and Alzheimer's Disease

Abstract: Parkinson's disease is characterized by massive degeneration of the melanized dopaminergic neurons in the substantia nigra. The functional capacity of the surviving nigral neurons is affected, as indicated by the subnormal levels of tyrosine hydroxylase (TH) mRNA in these neurons and the presence in the parkinsonian mesencephalon of melanized neurons lacking TH immunoreactivity. This is apparently in contradiction with the known overactivity of dopamine synthesis and release that occurs in the remaining dopaminergic terminals. To test the ability of the surviving neurons to express TH protein, a semiquantitative immunocytochemical method was developed. The relative amounts of TH were estimated with a computer-assisted image analysis system in the dopaminergic neurons of representative mesencephalic sections of control and parkinsonian brains and for comparison in brains from patients with Alzheimer's disease. In control brains, the mean TH content per neuron differed from one subject to another and between the different dopaminergic cell groups of the mesencephalon in the same subject. Within a given dopaminergic region, the level of TH was variable among neurons. In patients with Parkinson's disease, the ratio of TH protein content per neuron in the substantia nigra by reference to that of the central gray substance was reduced. In patients with Alzheimer's disease, the amount of TH was selectively reduced in the remaining dopaminergic neurons of the ventral tegmental area, a region characterized by a loss in dopaminergic neurons. The decrease in cellular TH content might therefore be related to the presence of the neurodegenerative process in the area considered. In patients with Parkinson's disease, the incapacity of the surviving neurons to express normal TH levels may reduce the efficiency of the hyperactivity mechanisms that develop in the remaining striatal dopaminergic terminals.