Peptidase increase accompanying growth of the larval salivary gland of Drosophila melanogaster

1. The larval salivary gland of Drosophila melanogaster offers an opportunity to study growth in a tissue in which no cell division occurs but in which the cells increase in size. 2. Measurements of alanylglycine (AG)-peptidase content have been made in three stocks of Drosophila melanogaster at different growth stages of the larval salivary gland, and have been correlated with its total nitrogen and volume. 3. During the prepupal instar, the AG-peptidase content of the gland increases parallel with total nitrogen but decreases when histolysis of the gland begins. Conversely, a benzoyl-l-arginineamide-hydrolyzing endopeptidase is not measurable until histolysis sets in. 4. In the final larval growth period of a giant mutant, there is a concomitant increase in peptidase, total nitrogen, and volume of the gland. 5. A similar association of peptidase content and total nitrogen is found in comparing glands of different sizes from the giant stock, at the time of maximal peptidase content in the prepupa. 6. The data are interpreted as evidence for an association of AG-peptidase with growth of the cells in the gland. This agrees with the earlier interpretation by Linderstrøm-Lang and Holter of data obtained from study of more complex tissues. 7. A survey of the available measurements of peptidase content in other organisms shows that wherever an increase of cell substance occurs, peptidase content increases. Conversely, peptidase remains constant where cell division is unaccompanied by an increase of cell substances. 8. The joint association of peptidases and pentosenucleic acids with protein synthesis is pointed out. 9. The possiblity is considered that peptidases may be essential parts of a unit in which coupled reactions necessary for protein synthesis occur. The rôle of the peptidases in this system is discussed. They may act either synthetically to form new peptide linkages (problematic), or hydrolytically to mobilize the necessary specific amino acids.

Peptidase activities of extracts of salivary glands of Drosophila melanogaster

1. Peptide-splitting enzymes have been studied in buffered glycerine extracts of larval salivary glands of three stocks of Drosophila melanogaster. 2. The ultraviolet absorption spectrum of the glycerine extracts indicates the presence of a considerable amount of nucleic acid. 3. Alanylglycine (AG), leucylglycine (LG), leucylglycylglycine (LGG), glycylglycine (GG), and diglycylglycine (GGG) are split by the gland extracts in descending order of activity. 4. Of the various metals added, manganese was the only one found to give clear cut activation and that only with LGG as substrate. Cysteine inhibited the splitting of both AG and LG. 5. Comparison of the data with those published indicates the presence in the extracts in descending order of activity (at pH 7.6, 40°C.) of at least four enzymes: an AG-dipeptidase, an LG-dipeptidase, a leucineaminopeptidase, and possibly an aminopolypeptidase. 6. Optimum conditions for the measurement of the enzyme splitting AG were determined. The pH activity and kinetic data are typical for an AG-dipeptidase. 7. An enzyme (probably cathepsin II) splitting benzoyl-l-arginineamide (pH 5.0) with cysteine activation was observed to occur with very low activity in gland extracts.

An electron microscope study of salivary gland chromosomes by the replica method

A method for preparing replicas of salivary gland chromosomes for electron microscopy is described. Electron micrographs of these replicas show that the giant chromosomes are composed of a series of small granules of approximately equal size arranged transversely across the chromosome. In stretched preparations a linear network of filaments appears between the rows of granules. These fibers cannot be traced between corresponding granules of more than two consecutive rows. When the chromosomes are digested by desoxyribonuclease, these fibers disappear and only amorphous material remains between the bands. The characteristics of the strands suggest that they are artifacts produced when the chromosomes are stretched. The small granules are composed of desoxyribonucleic acid and at least one other component, probably a protein. The nucleic acid seems to lie at least in part on the surface of each granule.

Occurrence and some properties of eledoisin in extracts of posterior salivary glands of Eledone

The posterior salivary glands of Eledone, alone among the tissues of this molluscan species, contain eledoisin, an endecapeptide with activity on blood vessels and extravascular smooth muscles. The salivary glands of Octopus vulgaris and O. macropus lack the polypeptide. Eledoisin is present, in amounts ranging from 20 to 160 mug/g fresh tissue, at all stages of growth and in every season; however, conspicuous differences in the eledoisin content were observed in different groups of animals. Eledoisin is fairly stable in intact salivary glands stored on ice. The most suitable solvent for its extraction is 70 to 80% methanol. Better results are also obtained with boiling diluted acetic acid, than with ethanol, whereas extraction with acetone gives unsatisfactory yields. Eledoisin is stable in neutral or slightly acid medium, but is rapidly destroyed by strong acids and even more rapidly by strong alkalis. It is quickly and completely inactivated by chymotrypsin, and somewhat more slowly and incompletely by trypsin. Carboxypeptidase is ineffective. Passage of crude salivary extracts of Eledone through an alumina column yields preparations of eledoisin which may be considered pure from a biological point of view.

Electron microscope studies on salivary gland cells. I. The nucleus of Bradysia mycorum Frey (Sciaridae), with special reference to the nucleolus

Salivary glands were fixed in cold 1 per cent osmium tetroxide in veronal-acetate buffer containing sucrose and embedded in methacrylate mixture or Araldite. The salivary gland nuclei of sciarids show a continuous production of nucleoli, which remain multiple and not consolidated into a single structure. The earliest recognizable nucleoli, which we call "elementary nucleoli," are aggregations of a few paired 40 A fibrils and a few 150 A particles, at many points within chromosome bands. Further development consists of the detachment of the elementary nucleoli from their points of origin and their subsequent mutual coalescence. As a result, dense patches of nucleolar material are formed which become large nucleoli at the surface of chromosomes, either attached to the band or free. The fully formed nucleoli have a characteristic dual structure with a narrow dense periphery and a broader less dense internum. Fibrils and particles are present in both regions, and the difference in density reflects differences in the packing of the two structural elements. The duality in structure is lost in later stages. The nucleolar fibrils appear to be similar to the chromosomal fibrils. The 150 A particles in nucleoli, chromosomes, and nuclear sap seem identical. The significance of these observations is discussed for nucleologenesis in general.

SEPARATION OF THE SALIVARY AND MOTOR RESPONSES IN INSTRUMENTAL CONDITIONING

If an instrumental conditioning schedule is arranged so that a dog must repeatedly perform a movement in response to one stimulus in order to secure the presentation of another stimulus, which is then followed by food, a virtually total separation of motor and salivary responses is observed. The first stimulus elicits the trained movement without salivation, and the second stimulus elicits salivation without instrumental responding. These experiments show a relative independence between classical and ìnstrumental conditioned responses and clarify the rather complex relations between the two in the usual experimental procedure.

FINE STRUCTURE OF DIFFERENTIATING MOUSE PANCREATIC EXOCRINE CELLS IN TRANSFILTER CULTURE

Fine structural observations have been made in the 11-day embryonic mouse of exocrine cells in pancreatic epithelium developing in tissue culture transfilter from salivary gland mesenchyme of the 13-day embryonic mouse. After 2 days in culture, the exocrine cells show increased cytoplasmic density, abundant ribosomes in aggregate or "rosette" form, and expanded profiles of rough-surfaced endoplasmic reticulum. After 3 and 4 days in culture, the cells exhibit continued expansion of the profiles of endoplasmic reticulum, increased amounts of Golgi membranes, and large areas of light density (prozymogen granules). After 5 days in culture, dense zymogen granules are present in the most highly differentiated cells. In addition, at the filter-epithelial surface, at 2 days, small fibers can be discerned which, after 4 days in culture, show obvious periodicity and are thought to be collagen. The significance of these changes, in relation to the mesenchymal effect, to the onset of specific synthesis and to the stabilization of differentiation is discussed.

THE EFFECT OF MENADIONE AND PHENAZINE METHOSULFATE ON THE TETRAZOLIUM REDUCTION SYSTEM UNDER HISTOCHEMICAL CONDITIONS

The influence of phenazine methosulfate and menadione on the activity of DPNH- and TPNH-tetrazolium reductase, succinic, lactic, and triphosphopyridine nucleotide-linked isocitric dehydrogenase were studied with reference to applied histochemistry. Fresh frozen sections of various tissues were employed in conjunction with nitro blue tetrazolium as the hydrogen acceptor.

Phenazine methosulfate was found to produce a variable effect upon staining, enhancing it or suppressing it according to incubation conditions. Suppression was most pronounced with higher concentrations. Menadione had no suppressive influence and was useful in increasing tetrazolium reduction. Its usefulness is, however, limited unless a soluble factor, possibly DT-(DPNH-TPNH)-diaphorase, can be prevented from diffusing into the medium, and "nothing dehydrogenase" is selectively inactivated.

DEVELOPMENTAL STUDIES OF THE DIPTERAN SALIVARY GLAND. II. DNASE ACTIVITY IN CHIRONOMUS THUMMI

The deoxyribonuclease (DNase) activity of the dipteran (Chironomus thummi) salivary gland, measured both enzymatically and immunochemically, increases about 7-fold with the onset of metamorphosis. The increase in DNase activity occurs at a time when the activities of other enzymes and the total protein content are decreasing. The increased DNase activity is followed by glandular destruction. It is suggested that the alterations of this activity may be regulated by the activities of specific chromosomal sites, and that the enzyme may, at least in part, account for the glandular destruction observed at the time of increased enzyme activity.

LEAKAGE OF TRANSMITTERS IN SALIVARY GLANDS

Salivary secretion evoked by sympathetic stimulation or by injection of guanethidine, adrenaline or synephrine is slightly reduced by parasympathetic antagonists in doses which abolish the secretory responses to stimulation of the parasympathetic nerve. Similarly, an adrenaline antagonist caused a small diminution of the salivary flow elicited by parasympathetic stimulation or by injection of methacholine chloride. Secretion caused by pilocarpine could be accelerated by physostigmine. We conclude that transmitter leaks in subliminal concentrations, as far as secretion is concerned, from the sympathetic and parasympathetic postganglionic nerve endings.

STUDIES ON AN EPITHELIAL (GLAND) CELL JUNCTION. II. SURFACE STRUCTURE

The surface structure of a gland epithelium (Drosophila salivary gland), particularly that at the junction between cells, was examined under the electron microscope. The junctional surface, which in the preceding paper was shown to be highly permeable to ions, has the following structural characteristics. About two-thirds of it are profusely infolded; the surface membranes of adjoining cells interdigitate and present desmosomes. The width of the intercellular space varies considerably. The remainder of the junctional surface, the third that abuts on the lumen, is rather straight. Here, the cell membranes are aligned parallel at a distance of 150 A, and interconnected at regular intervals of 100 A. The connecting material has a high electron opacity, and is about as thick as the cell membranes, but, unlike the latter, has no resolvable unit membrane structure. The surface at the cell base, which in the preceding paper was shown to be rather impermeable, is infolded and resembles the infolded junctional region. The luminal surface exhibits microvilli. Critical surface dimensions are given, and the implications of surface structure in intercellular permeability are discussed.

PRESERVATION OF TOTAL, LYO-, AND DESMOENZYME ACTIVITY IN MAMMALIAN SALIVARY GLANDS FOLLOWING CHLORAL HYDRATE FORMALIN FIXATION

Acid phosphatase, alkaline phosphatase, nonspecific esterase, pseudocholinesterase, leucine aminopeptidase, and β-d-galactosidase activities of parotid and submandibular salivary glands were evaluated in six animal species. Assays for total enzyme, lyoenzyme, and demoenzyme were performed on unfixed and chloral hydrate formalin (CHF) fixed frozen cryostat sections.

Following fixation lyoenzyme (soluble fraction) activity exhibited extreme reduction for all enzymes except pseudocholinesterase, while the demoenzyme (insoluble fraction) activity of acid phosphatase, nonspecific esterase, pseudocholinesterase, and β-d-galactosidase was maintained at a high level or increased. Since removal of lyoenzyme activity and retention of desmoenzyme activity are requisites in histochemical localization, this fixative may be the preferred method for handling tissues prior to the localization of the above cited enzymes.

Several hypotheses are proposed to explain the increased desmoenzyme (nonspecific esterase and β-d-galactosidase) noted subsequent to fixation.

STUDIES ON AN EPITHELIAL (GLAND) CELL JUNCTION. I. MODIFICATIONS OF SURFACE MEMBRANE PERMEABILITY

Membrane permeability of an epithelial cell junction (Drosophila salivary gland) was examined with intracellular microelectrodes and with fluorescent tracers. In contrast to the non-junctional cell membrane surface, which has a low permeability to ions (10^-4 mho/cm²), the junctional membrane surface is highly permeable. In fact, it introduces no substantial restriction to ion flow beyond that in the cytoplasm; the resistance through a chain of cells (150 Ω cm) is only slightly greater than in extruded cytoplasm (100 Ω cm). The diffusion resistance along the intercellular space to the exterior, on the other hand, is very high. Here, there exists an ion barrier of, at least, 10⁴Ω cm². As a result, small ions and fluorescein move rather freely from one cell to the next, but do not leak appreciably through the intercellular space to the exterior. The organ here, rather than the single cell, appears to be the unit of ion environment. The possible underlying structural aspects are discussed.

SOME ELECTRICAL PROPERTIES OF A NUCLEAR MEMBRANE EXAMINED WITH A MICROELECTRODE

Electrical potential and resistance were measured with microelectrodes in in situ and isolated nuclei of gland cells of Drosophila flavorepleta. The nucleus-cytoplasm boundary was found to be rather impermeable to ion diffusion. It presents a resistance of the order of 1 Ω cm² and sustains a "resting" potential, the nucleoplasm being about 15 mv negative with respect to the cytoplasm. Both the resistance and potential appear to be associated with the nuclear membrane: the potential declines to zero and the resistance to a fraction of its original value, when the membrane is perforated experimentally.

DEMONSTRATION OF PEROXIDASE ACTIVITY IN TISSUE SECTIONS

By using an improved benzidine technique, peroxidase activity can be demonstrated in various locations in mammalian tissues. A relatively formalin resistant enzyme is found in hemoglobin and is also associated with mitochondria of striated muscle and heart. A somewhat less formalin resistant peroxidase occurs in the granules of myeloid and mast cells. A relatively formalin sensitive peroxidase is present in a number of additional locations, e.g. the acinar cells in thyroid and salivary gland, the medulla of the kidney, in hair follicles of the guinea pig skin and Kupffer cells of the liver.

ELECTROPHORESIS STUDY OF EXTRACTS OF SUBMAXILLARY SALIVARY GLANDS FROM NATURALLY RABID DOGS

Rabies virus in submaxillary salivary glands from naturally infected dogs was investigated by a paper electrophoresis technique, and the virus activity was quantitated by intracerebral titration in mice. Extracts from these salivary glands were found to contain (a) 10(4) to 10(6) mouse ICLD (50) units of wild rabies seed and (b) a protein complex that migrated electrophoretically in the albumin band and more conspicuously in the beta and gamma bands of normal horse serum. The protein complex was interpreted to comprise aggregates of neutralizing antirabies antibody.