Three patterns of mitochondrial DNA nucleotide divergence in the meadow vole,Microtus pennsylvanicus

Summary The DNA sequence was determined for the cytochrome c oxidase II (COII), tRNA^Lys, and ATPase 8 genes from the mitochondrial genome of the meadow vole, Microtus pennsylvanicus. When compared to other rodents, three different patterns of evolutionary divergence were found. Nucleotide variation in tRNA^Lys is concentrated in the TC loop. Nucleotide variation in the COII gene in three genera of rodents (Microtus, Mus, Rattus) consists predominantly of transitions in the third base positions of codons. The predicted amino acid sequence in highly conserved (>92% similarity). Analysis of the ATPase 8 gene among four genera (Microtus, Cricetulus, Mus, Rattus) revealed more detectable transversions than transitions, many fixed first and second position mutations, and considerable amino acid divergence. The rate of nucleotide substitution at nonsynonymous sites in the ATPase 8 gene is 10 times the rate in the COII gene. In contrast, the estimated absolute mutation rate as determined by analysis of nucleotide substitutions at fourfold degenerate sites probably is the same for the two genes. The primary sequences of the ATPase 8 and COII peptides are constrained differently, but each peptide is conserved in terms of predicted secondary-level configuration.     

THE FLORAL AND EXTRA-FLORAL NECTARIES OF PASSIFLORA. I. THE FLORAL NECTARY

Floral nectary development and nectar secretion in three species of Passiflora were investigated with light and electron microscopy. The nectary ring results from the activity of an intercalary meristem. Increased starch deposition in the amyloplasts of the secretory cells parallels maturation of the nectary phloem. Large membrane-bound protein bodies are observed consistently in phloem parenchyma cells, but their function is presently unknown. The stored starch serves as the main source of nectar sugars at anthesis. Plastid envelope integrity is maintained during starch degradation, and there is no evidence of participation of endoplasmic reticulum or Golgi in the secretion of pre-nectar. It is concluded that in these starchy nectaries granulocrine secretion, commonly reported for floral nectaries, does not occur.     

Changes in plasma-membrane-associated filaments during endocytosis and exocytosis in polymorphonuclear leukocytes

We examined the filaments associated with the cytoplasmic surface of the plasma membrane in rabbit exudate PMNs during phagocytosis of particles, or during “frustrated phagocytosis” with exocytosis of storage granules. Cells were plated onto yeast particles glued to coverslips with polylysine or onto coverslips coated with sheets of heat-agglutinated IgG. After periods ranging from 1 to 15 min, we disrupted the cells by a jet of salt solution and exposed their inner membranes. These broken cells were fixed immediately and processed for SEM. Whole cells were also prepared for SEM or TEM. At the site of PMN adherence to an opsonized yeast particle, a network of globular centers and thin, branched filaments appears on the cytoplasmic surface of the plasma membrane, while the outstretching lamellipodia contain a mesh of such filaments but no globular centers. Within 1 to 2 minutes, these structures disappear from the invaginating portion of the developing vacuole, and the cell's storage granules fuse with the barren membrane regions. These activities occur in rapid sequence over the vacuolar membrane after the first contact, until the phagocytosed particle is wholly encircled by a smooth, loose membrane, separated from the cell surface. A comparable filament pattern or complex was seen during “frustrated phagocytosis” on IgG sheets. At times between 1 and 5 min after plating, the cytoplasmic surfaces of these adherent membranes contain denuded central regions and peripheral nets of globular centers with radiating, thin, branched filaments. Granules apparently fuse with the bare areas. Thus we have obtained evidence of filament association with the plasma membrane at sites of adherence (to phagocytosable or nonphagocytosable surfaces) and have traced the subsequent disappearance of the filaments with degranulation.     

Polysomal and non-polysomal messenger RNA in neuroblastoma cells: Lack of correlation between polyadenylation or initiation efficiency and messenger RNA location

Neuroblastoma cytoplasm was fractionated on sucrose gradients into polysomes (>90 S) and non-polysomal particles (<90 S). Purified RNA from these fractions was translated using a wheat germ lysate and translation products were compared by two-dimensional gel electrophoresis. Non-polysomal messenger RNA directed the synthesis of a specific subset of polysomal mRNA translation products. Careful comparison of individual translation products demonstrated that specific mRNAs were not randomly distributed between polysomes and the non-polysomal fraction.Fractionation of both RNA populations into polyadenylated (poly(A)⁺) and non-adenylated (poly(A)^?) species indicated that specific, abundant non-polysomal mRNAs were not less adenylated than their polysomal counterparts. Furthermore, comparison of translation products from assays of subsaturating and supersaturating RNA concentrations demonstrated that no simple correlation could be made between the relative initiation efficiency of a specific mRNA and its distribution between polysomes and non-polysomal particles.     

An endogenous motor program for sand crab uropods

A stereotyped pattern of spontaneous, rhythmic bursting in motoneurons of three prinicipal uropod muscles in the sand crab Emerita analoga has been recorded from a deafferented chain of the foru most-posterior abdominal ganglia. This endogenous motor program resembles the electromyogram pattern recorded from return-stroke and power-stroke muscles in swimming crabs in that (1) latencies of power-stroke bursts and burst periods are positively correlated with each other and (2) durations of power-stroke bursts are brief and mearly invarient. The endogenous program differs from the electromyogram pattern in having longer periods and return-stroke bursts which are brief and sporadic. The neural oscillator underlying the endogenous motor program, therefore, appears to drive the power stroke. Circumstantial evidence suggests that it may also inhibit return-stroke motoneurons concurrently with excitation of the power-stroke excitor.     

Spontaneous cell hybridization of somatic cells present in sperm suspensions

Electron microscopic evidence suggests that sperm can be spontaneously incorporated by cultured cells but cytogenetic and biochemical evidence indicate that sperm do not introduce new genes into such cells with detectable frequency. Sperm suspensions from mouse or Chinese hamster epididymis or human semen were added to cultures of RAG, a mouse cell line which dies in HAT medium because of HPRT deficiency. In EMs, sperm appeared to be readily phagocytized and degraded by the cells. When sperm-treated cultures were transferred to HAT medium resistant clones arose at a frequency of about 10⁻⁶, or at least 25× the reversion rate of RAG. Most HAT-resistant clones had HPRT activity which migrated electrophoretically like HPRT of the sperm donor species, though one was apparently a spontaneous RAG revertant. Most HAT-resistant clones had some chromosomes of the sperm donor species. In human sperm× RAG clones, the array of human chromosomes suggested that the human parent had been diploid rather than haploid; some cells contained both homologues of a polymorphic pair and some contained both X and Y. Furthermore, some sperm suspensions plated alone into flasks generated colonies, thus revealing the presence of low numbers of viable somatic cells. Presence of contaminating somatic cells in a sperm suspension was correlated with ability to induce HAT-resistant colonies when the suspension was added to RAG cells. Taken together, the data suggest that correction of the HPRT deficiency of RAG by sperm suspensions occurs at very low frequency and is probably due to efficient spontaneous fusion of low numbers of contaminating somatic cells with RAG cells.     

Ultrastructure and peroxidase cytochemistry of normal human leukocytes at birth

At birth, differential and white blood cell counts of normal newborn infants are strikingly different from those of adults in that the number of leukocytes is increased and immature cells course through the circulation. In this study, our intent was to examine normal neonatal cord blood by electron microscopy and peroxidase cytochemistry to determine whether any detectable differences exist in the leukocytes of neonatal and adult blood. This investigation was undertaken because newborn infants have an increased susceptibility to infection, and alterations in phagocyte function have been implicated as the cause. Cord blood was found to contain mature leukocytes of all kinds, similar in ultrastructure and peroxidase localization to those of adults. Moreover, as indicated earlier by light microscopy, immature forms (normally found only in adult bone marrow) were present in the blood of newborns. We found that nearly all cell lines were represented in the neonatal circulation by such developmental forms as promyelocytes, myelocytes, promonocytes, erythroblasts, megakaryocytes, rare unidentifiable blasts, and dividing cells—all resembling their counterparts in adult bone marrow. With the techniques used here, neonatal leukocytes were similar to those of the adult in ultrastructure and peroxidase localization, although some had been mobilized into the blood in a remarkably immature state. This study, the first of its kind, will serve as a helpful background for future investigations of acquired, genetic or neoplastic leukocyte abnormalities which may be discovered at birth.