Interneuronal and glial-neuronal gap junctions in the lamina ganglionaris of the compound eye of the housefly,Musca domestics

Summary The cell-body layer of the lamina ganglionaris of the housefly, Musca domestica, contains the perikarya of five types of monopolar interneuron (L1–L5) along with their enveloping neuroglia (Strausfeld 1971). We confirm previous reports (Trujillo-Cenóz 1965; Boschek 1971) that monopolar cell bodies in the lamina form three structural classes: Class I, Class II, and midget monopolar cells. Class-I cells (L1 and L2) have large (8–15 m) often crescentshaped cell bodies, much perinuclear cytoplasm and deep glial invaginations. Class-II cells (L3 and L4) have smaller perikarya (4–8 m) with little perinuclear cytoplasm and no glial invaginations. The midget monopolar cell (L5) resides at the base of the cell-body layer and has a cubshaped cell body. Though embedded within a reticulum of satellite glia, the L1–L4 monopolar perikarya and their immediately proximal neurites frequently appose each other directly. Typical arthropod (-type) gap junctions are routinely observed at these interfaces. These junctions can span up to 0.8 m with an intercellular space of 2–4 nm. The surrounding nonspecialized interspace is 12–20 nm. Freezefracture replicas of monopolar appositions confirm the presence of -type gap junctions, i.e., circular plaques (0.15–0.7 m diam.) of large (10–15 nm) E-face particles. Gap junctions are present between Class I somata and their proximal neurites, between Class I and Class II somata and proximal neurites, and between Class II somata. Intercartridge coupling may exist between such monopolar somata. The cell body and proximal neurite of L5 were not examined. We also find that Class I and Class II somata are extensively linked to their satellite glia via gap junctions. The gap width and nonjunctional interspace between neuron and glia are the same as those found between neurons. The particular arrangement and morphology of lamina monopolar neurons suggest that coupling or low resistance pathways between functionally distinct neurons and between neuron and glia are probably related to the metabolic requirements of the nuclear layer and may play a role in wide field signal averaging and light adaptation.     

Evolution of the dispersed SUC gene family of Saccharomyces by rearrangements of chromosome telomeres.

The SUC gene family of Saccharomyces contains six structural genes for invertase (SUC1 through SUC5 and SUC7) which are located on different chromosomes. Most yeast strains do not carry all six SUC genes and instead carry natural negative (suc0) alleles at some or all SUC loci. We determined the physical structures of SUC and suc0 loci. Except for SUC2, which is an unusual member of the family, all of the SUC genes are located very close to telomeres and are flanked by homologous sequences. On the centromere-proximal side of the gene, the conserved region contains X sequences, which are sequences found adjacent to telomeres (C. S. M. Chan and B.-K. Tye, Cell 33:563-573, 1983). On the other side of the gene, the homology includes about 4 kilobases of flanking sequence and then extends into a Y' element, which is an element often found distal to the X sequence at telomeres (Chan and Tye, Cell 33:563-573, 1983). Thus, these SUC genes and flanking sequences are embedded in telomere-adjacent sequences. Chromosomes carrying suc0 alleles (except suc20) lack SUC structural genes and portions of the conserved flanking sequences. The results indicate that the dispersal of SUC genes to different chromosomes occurred by rearrangements of chromosome telomeres.     

Distribution,biology and hybridization of Scaphirhynchus albus and S. platorynchus in the Missouri and Mississippi rivers

Synopsis Scaphirhynchus albus and S. platorynchus were studied in Missouri during 1978–1979 to assess their distribution and abundance, to obtain information on their life histories, and to identify existing or potential threats to their survival. S. platorynchus was collected in substantial numbers (4355 specimens) at all 12 sampling stations in the Missouri and Mississippi rivers, while only 11 S. albus were captured from 6 stations. Twelve specimens identified in the field as hybrids between the two species were captured from 4 stations. Morphometric and meristic comparisons of presumed hybrids with the parent species, using cluster and principal components analyses, demonstrated intermediacy of most specimens identified in the field as hybrids. Aquatic insects comprised most of the diet of S. platorynchus and S. albus, but S. albus and the hybrids had consumed considerable quantities of fish. S. albus grew more rapidly than S. platorynchus, while the growth of hybrids was intermediate. Hybridization appears to be a recent phenomenon, resulting from man-caused changes in the big-river environment. Hybridization may be a threat to survival of S. albus in the study streams.     

Genes Affecting the Regulation of SUC2 Gene Expression by Glucose Repression in SACCHAROMYCES CEREVISIAE

Mutants of Saccharomyces cerevisiae with defects in sucrose or raffinose fermentation were isolated. In addition to mutations in the SUC2 structural gene for invertase, we recovered 18 recessive mutations that affected the regulation of invertase synthesis by glucose repression. These mutations included five new snf1 (sucrose nonfermenting) alleles and also defined five new complementation groups, designated snf2, snf3, snf4, snf5, and snf6. The snf2, snf4, and snf5 mutants produced little or no secreted invertase under derepressing conditions and were pleiotropically defective in galactose and glycerol utilization, which are both regulated by glucose repression. The snf6 mutant produced low levels of secreted invertase under derepressing conditions, and no pleiotropy was detected. The snf3 mutants derepressed secreted invertase to 10-35% the wild-type level but grew less well on sucrose than expected from their invertase activity; in addition, snf3 mutants synthesized some invertase under glucose-repressing conditions.--We examined the interactions between the different snf mutations and ssn6, a mutation causing constitutive (glucose-insensitive) high-level invertase synthesis that was previously isolated as a suppressor of snf1. The ssn6 mutation completely suppressed the defects in derepression of invertase conferred by snf1, snf3, snf4 and snf6, and each double mutant showed the constitutivity for invertase typical of ssn6 single mutants. In contrast, snf2 ssn6 and snf5 ssn6 strains produced only moderate levels of invertase under derepressing conditions and very low levels under repressing conditions. These findings suggest roles for the SNF1 through SNF6 and SSN6 genes in the regulation of SUC2 gene expression by glucose repression.     

A method for combined gross skeletal staining and Feulgen staining of embryonic chick tissues

This paper describes a combined technique for gross skeletal staining and Feulgen staining of avian embryonic limbs. The gross skeletal stain uses Victoria blue B, and the Feulgen stain is done en bloc before the skeletal stain is applied. The method has been useful in determining the cellular origins of supernumerary structures arising from experiments in which quail wing mesoderm is grafted into chick wing buds.     

Comparison of denitrification by Pseudomonas stutzeri, Pseudomonas aeruginosa, and Paracoccus denitrificans.

A comparison was made of denitrification by Pseudomonas stutzeri, Pseudomonas aeruginosa, and Paracoccus denitrificans. Although all three organisms reduced nitrate to dinitrogen gas, they did so at different rates and accumulated different kinds and amounts of intermediates. Their rates of anaerobic growth on nitrate varied about 1.5-fold; concomitant gas production varied more than 8-fold. Cell yields from nitrate varied threefold. Rates of gas production by resting cells incubated with nitrate, nitrite, or nitrous oxide varied 2-, 6-, and 15-fold, respectively, among the three species. The composition of the gas produced also varied markedly: Pseudomonas stutzeri produced only dinitrogen; Pseudomonas aeruginosa and Paracoccus denitrificans produced nitrous oxide as well; and under certain conditions Pseudomonas aeruginosa produced even more nitrous oxide than dinitrogen. Pseudomonas stutzeri and Paracoccus denitrificans rapidly reduced nitrate, nitrite, and nitrous oxide and were able to grow anaerobically when any of these nitrogen oxides were present in the medium. Pseudomonas aeruginosa reduced these oxides slowly and was unable to grow anaerobically at the expense of nitrous oxide. Furthermore, nitric and nitrous oxide reduction by Pseudomonas aeruginosa were exceptionally sensitive to inhibition by nitrite. Thus, although it has been well studied physiologically and genetically, Pseudomonas aeruginosa may not be the best species for studying the later steps of the denitrification pathway.     

Growth of the masseter muscle in rhesus monkeys (Macaca mulatta)

The growth of the masseter muscle in eight infant, juvenile, and adolescent female rhesus monkeys (M. mulatta) was examined over a 2.5 year period using serial radiographic cephalometric techniques with the aid of radiopaque muscle markers. The radiopaque markers, which are composed of small pieces of root canal broach inserted into the muscle belly, make it possible to determine longitudinal masseter muscle growth as well as migration of the masseter muscle relative to the mandible. It was found that the masseter muscle increased in length by 64% during the total growth period, most of which occurred between 6 and 18 months of age. Relative to the cranium, the masseter muscle grew markedly inferiorly and only slightly posteriorly. Relative to the mandible, the masseter migrated in a posterior and slightly superior direction, keeping pace with the ramus and condyle as they grew posteriorly and posterosuperiorly throughout the study period. It was concluded that: 1) radiopaque muscle markers are a valuable tool for analysis of muscle growth and alteration of muscle location; 2) the masseter muscle in the rhesus monkey undergoes elongation, probably due to addition of sarcomeres at the fiber-tendon junctions; and 3) posterior migration of the masseter muscle relative to the corpus of the mandible, probably due to the nature of its periosteal attachment, results in a stability of the anteroposterior position of the masseter muscle despite the anterior displacement of the mandible.     

A highly antigenic proteoglycan-like component of cholinergic synaptic vesicles

A monoclonal antibody, tor70, recognizes an antigenic determinant on the inside surface of synaptic vesicles, purified from the electric organ of Narcine brasiliensis. The antigenic determinant appears to be unique to vesicles since it co-purifies with vesicle content and is blocked by an antiserum specific for synaptic vesicle antigens. Immunoblotting of vesicle proteins after sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that the antigen has a low heterogeneous electrophoretic mobility and corresponds to a major protein component of pure synaptic vesicles. Synaptic vesicles contain a proteoglycan-like material since proteolytic digestion yields a ruthenium red-binding material that migrates during electrophoresis with a mammalian heparin standard. The only major vesicle component with which the proteoglycan-like material co-elutes during chromatography on Sepharose 6B is the material recognized by tor70. The antigen adsorbs specifically to beads coated with the lectin wheat germ agglutinin. Isolation of the tor70 antigen by velocity sedimentation in sodium dodecyl sulfate-sucrose gradients shows it to contain glucosamine (0.75 nmol/microgram of protein) and uronic acid but no galactosamine. Earlier work has shown that specific antiserum to pure synaptic vesicles could be used to identify nerve terminals, quantitate vesicle components, purify membranes, and monitor exocytosis. We now know that one of the components recognized by the antiserum is a molecule with properties of a proteoglycan, attached to the inside surface of vesicle membranes.     

Occurrence and seasonal variation of 19-norcholest-4-en-3-one and 3 beta-monohydroxy sterols in the Californian gorgonian, Muricea californica

The first natural occurrence of 19-norcholestenone is reported, together with 17 sterols and one other delta 4-3-ketone in the extracts of the Californian gorgonian, Muricea californica (Aurivillius). Six additional demethyl sterols and five additional 4-monomethyl sterols which remain unidentified were also detected. Lipid extracts of M. californica from a winter and summer collection were split by various chromatographic methods into free sterol, steryl ester, and steryl conjugate fractions. Sterol compositions (determined by CG and CG-MS) of each fraction, subsequent to hydrolysis, are tabulated and discussed with respect to plausible origins of observed variations. The possible relationship of the Muricea 19-nor-steroidal ketone to other naturally occurring 19-nor-steroids is discussed.