Protein Synthesis In Glands Research Articles

Parasympathetic non-adrenergic, non-cholinergic transmission in rat parotid glands: Effects of cholecystokinin-A and -B receptor antagonists on the secretory response

Recent studies show I.V. administered pentagastrin and cholecystokinin to evoke protein/amylase secretion from the rat parotid gland and to stimulate gland protein synthesis, the two phenomena being abolished by cholecystokinin receptor antagonists. In the rat parotid gland, non-adrenergic, non-cholinergic transmission mechanisms contribute to secretion of fluid and protein/amylase. Since cholecystokinin may act as a neurotransmitter, activation of cholecystokinin receptors of the gland might contribute to the parasympathetic nerve-evoked secretion. In this study, the parasympathetic innervation was stimulated in non-atropinized (in periods of 2 min) or atropinized (in periods of 3 min) pentobarbitone-anaesthetized rats before and after administration of the cholecystokinin-A receptor antagonist lorglumide (48 mg/kg, I.V.) and the cholecystokinin-B receptor antagonist itriglumide (5.5 mg/kg, I.V.). The non-adrenergic, non-cholinergic transmission fatigues rapidly resulting in declining responses. Therefore, atropinized rats, not receiving the cholecystokinin receptor antagonists, had to serve as controls. Neither at a stimulation frequency of 10 Hz nor of 40 Hz were the secretory responses of the atropinized rats affected by the receptor antagonists. After lorglumide, the saliva volume and the amylase output were (expressed as percentage of the response to the stimulation period before the administration of the antagonist) 98.0 ± 3.8% ( vs. control 91.1 ± 4.0%) and 91.9 ± 4.9% ( vs. 87.7 ± 3.7%) at 10 Hz, respectively, and 79.8 ± 4.5% ( vs. 77.3 ± 2.1%) and 73.6 ± 5.3% ( vs. 71.7 ± 2.3%) at 40 Hz, respectively. After itriglumide, the corresponding percentage figures for saliva volume and amylase output were, at 10 Hz, 99.5 ± 8.9% ( vs. 92.0 ± 2.8%) and 95.8 ± 11.8% ( vs. 89.2 ± 6.4%), respectively, and, at 40 Hz, 74.0 ± 3.1% ( vs. 79.6 ± 2.2%) and 66.6 ± 3.3% ( vs. 63.9 ± 6.0%), respectively. Similarly, the antagonists were without effect on the parotid secretory responses of non-atropinized rats subjected to stimulation at 10 Hz. Thus, under physiological conditions, the cholecystokinin receptors of the parotid gland are likely to be stimulated by circulating hormones rather than by nervous activity.

Molecular aspects of viviparous reproductive biology of the tsetse fly ( Glossina morsitans morsitans): Regulation of yolk and milk gland protein synthesis

Tsetse fly (Diptera: Glossinidae) viviparous reproductive physiology remains to be explored at the molecular level. Adult females carry their young in utero for the duration of embryonic and larval development, all the while supplying their offspring with nutrients in the form of a “milk” substance secreted from a modified accessory gland. Flies give birth to fully developed third instar larvae that pupariate shortly after birth. Here, we describe the spatial and temporal expression dynamics of two reproduction-associated genes and their products synthesized during the first and second gonotrophic cycles. The proteins studied include a putative yolk protein, Glossina morsitans morsitans yolk protein 1 (GmmYP1) and the major protein found in tsetse “milk” secretions ( Glossina morsitans morsitans milk gland protein, GmmMGP). Developmental stage and tissue-specific expression of GmmYP1 show its presence exclusively in the reproductive tract of the fly during oogenesis, suggesting that GmmYP1 acts as a vitellogenic protein. Transcripts for GmmMGP are present only in the milk gland tissue and increase in coordination with the process of larvigenesis. Similarly, GmmMGP can be detected at the onset of larvigenesis in the milk gland, and is present during the full duration of pregnancy. Expression of GmmMGP is restricted to the adult stage and is not detected in the immature developmental stages. These phenomena indicate that the protein is transferred from mother to larvae as nourishment during its development. These results demonstrate that both GmmYP1 and GmmMGP are involved in tsetse reproductive biology, the former associated with the process of oogenesis and the latter with larvigenesis.

Nitric oxide-dependent protein synthesis in parotid and submandibular glands of anaesthetized rats upon sympathetic stimulation or isoprenaline administration.

In anaesthetized female rats, the beta-adrenoceptor agonist isoprenaline was intravenously infused (20 microg kg(-1) min(-1)) for 30 min or the ascending cervical sympathetic nerve trunk was intermittently stimulated (50 Hz, 1 s every tenth second) on one side for 30 min. The incorporation of [3H]leucine into trichloroacetic acid (TCA)-insoluble material was used as an index of protein synthesis. In response to isoprenaline, the [3H]leucine incorporation increased by 79% in the parotid glands and by 82% in the submandibular glands. The neuronal type NO-synthase inhibitor N-PLA, reduced (P < 0.001) this response to 26% and 20%, respectively. Sympathetic stimulation under alpha-adrenoceptor blockade increased the [3H]leucine incorporation by 192% in the parotid glands and by 35% in the submandibular glands. N-PLA reduced the corresponding percentage figures to 86% (P < 0.01) and 8% (P < 0.05). When tested in the parotid glands, the non-selective NO-synthase inhibitor L-NAME reduced (P < 0.01) the nerve-evoked response to 91%. The increase in [3H]leucine incorporation in response to sympathetic stimulation under beta-adrenoceptor blockade was not affected by N-PLA in the parotid (139% versus 144%) and submandibular glands (39% versus 34%). In non-stimulated glands, the [3H]leucine incorporation was not influenced by the NO-synthase inhibitors. In conclusion, beta-adrenoceptor mediated salivary gland protein synthesis is largely dependent on NO generation by neuronal type NO-synthase, most likely of parenchymal origin.

Sulfur amino acid metabolism in the whole body and mammary gland of the lactating Saanen goat

Five multiparous Saanen goats in late lactation were infused with 35S-cysteine into the mammary gland via the external pudic artery. A further 2 goats were infused with 35S-methionine via the same artery and later with 35S-methionine into the jugular vein. Total uptake of cysteine from the arterial blood supply by the mammary gland was approximately 6% of the 35S-cysteine flux past the gland, whereas uptake of methionine was 30–40%. Total mammary uptake of cysteine was also lower than that of methionine when expressed as a percentage of whole body utilisation (6.5 and 14%, respectively). The uptake from the blood did not account for output in the milk for either cysteine or methionine. Both amino acids were highly conserved by the gland as shown by little release of any degraded constitutive protein amino acids and no evidence of oxidation products of either cysteine or methionine being released into the blood. Comparison of 35S activity in the milk from the infused and non-infused sides of the gland showed up to 10% trans-sulfuration of methionine to cysteine within the gland, none of which was exported in the venous drainage. Total ATP production by one side of the gland was 12.1 mol/day or 13 mmol/min.kg mammary tissue, of which 15% was required for gland protein synthesis. The experimental measurements from both the cysteine and methionine infusions were used to solve a model of gland amino acid uptake and partitioning. Modelling radioactivity of both amino acids in the blood, intracellular free pool, and milk protein suggested that a single intracellular pool cannot be the only source of amino acid for protein synthesis. The model also provides support for the hypothesis that a significant proportion of the uptake of at least some amino acids by the mammary gland is from intracellular hydrolysis of extracellularly derived peptides.

Mating and hormonal triggers regulate accessory gland gene expression in male Drosophila

Drosophila melanogaster males transfer accessory gland proteins, as part of their seminal fluid, to females during each mating. Since accessory gland proteins are important for male reproductive success, it is important that the male replenish the proteins he transferred during mating. Previous studies had shown that mating induces the resynthesis of accessory gland proteins, but since mating includes a set of stereotyped behavior patterns as well as the act of copulation, it was not known which aspect of the mating process induces accessory gland protein synthesis. By exposing males to females whose ovipositors had been sealed shut, we have shown that resynthesis of accessory gland proteins occurs only when seminal fluid is transferred to females. By applying juvenile hormone or 20-hydroxyecdysone topically to the cuticle of male flies, we showed that these hormones can act in vivo to stimulate the synthesis of accessory gland proteins to levels similar to those observed after mating.

Leucine and protein metabolism in the lactating dairy cow mammary gland: responses to supplemental dietary crude protein intake.

Mammary gland protein metabolism, determined by an arteriovenous difference technique, was monitored in four Holstein-Friesian dairy cows in response to supplemental dietary protein (provided as rumen-protected soyabean meal) during late lactation (weeks 24-30). Each cow was offered two isoenergetic diets composed of grass silage (170 g crude protein/kg dry matter) plus either a low (108 g/kg) or medium (151 g/kg) crude protein concentrate in a single crossover design involving two 21 d periods. On day 21, arteriovenous measurements across the mammary gland were made during a 13 h continuous i.v. infusion of [1-(13)C]leucine and with frequent (2 hourly) milk sampling during the final 6 h. Although total milk yield was slightly increased (+1 kg/d) by protein supplementation, milk protein yield was not significantly affected. Whole body protein flux (protein synthesis plus oxidation) was not significantly affected by supplementation. Total mammary gland protein synthesis (milk plus non-milk protein) was also not affected by supplementation but on both diets gland synthesis was always greater (by 20-59 percent) than milk protein output. The fractional oxidation rate of leucine by the mammary gland was significantly increased by protein supplementation (0-047 v. 0-136). Although the enrichment of leucine in secreted milk protein continued to increase, the final value (at 13 h) was 0-94 of the arterial plasma free leucine plateau value (not significantly different), suggesting almost exclusive use of plasma free leucine for milk protein synthesis. Based on current feeding schemes for dairy cattle, a fixed proportion (0-65 0-75) of the additional protein intake (+490 g/d) should have been partitioned into milk protein. Instead, leucine oxidation by the mammary gland was increased. Whether oxidation of other amino acids was also enhanced is unknown but if amino acid oxidation and the 'additional' non-milk protein synthesis occurring in the gland are not crucial to milk synthesis, then by reducing such activities improvements in the efficiency of converting absorbed amino acid into milk protein can be achieved.

Changes in general and specific protein synthesis that accompany ecdysteroid synthesis in stimulated prothoracic glands of Manduca sexta

The prothoracic glands of fifth instar Manduca sexta larvae respond to stimulation by the brain neuropeptide, prothoracicotropic hormone (PTTH), with a several-fold increase in the rate of ecdysteroid synthesis. Previous studies have shown that this response requires protein synthesis and that the action of PTTH can be mimicked by dibutyryl cAMP (dbcAMP) and the Ca 2+ ionophore, A23187. To further understand the role of protein synthesis in the response of prothoracic glands to PTTH, patterns of protein synthesis in stimulated glands were examined using glands incubated in vitro with [ 35S]methionine. All three agents caused an increase in the rate of ecdysteroid synthesis as well as an increase of up to 300% in the synthesis and/or accumulation of three proteins (p100, p70, and p“50”) within 2 h of stimulation. Changes in these three proteins were specific to the prothoracic gland, were not elicited by non-brain peptides and were not simply a result of increased general protein synthesis in the gland. Exposure of the glands to A23187 alone, or concurrently with dbcAMP, resulted in increased synthesis of p100, p70, p“50” and ecdysteroids but decreased general protein synthesis. Increased synthesis of these proteins could be detected within 15 min after initiating PTTH stimulation. The behavior of these three proteins makes them candidates for modulators of ecdysteroid synthesis in the prothoracic gland. The results suggest also that PTTH may activate two biochemical pathways in the gland: one path leading to increased synthesis of the p100, p70, and p“50” proteins and increased ecdysteroid synthesis, and the second leading to increased general protein synthesis. This second trophic effect is vulnerable to intracellular Ca 2+ changes that do not inhibit the first pathway.

Protein synthesis in the major salivary glands of the rat and the effects of re-feeding and acute ethanol injection

Rates of protein synthesis in the major salivary glands of the rat were accurately determined in vivo using the ‘flooding dose’ technique and the effects of reflex stimulation through feeding or acute ethanol treatment were assessed. Rats were divided into three groups. The control group was fasted overnight, the re-fed group was also fasted then re-fed the following morning and the third group received an intraperitoneal injection of ethanol after an overnight fast. In control rats the sublingual gland had a higher rate of protein synthesis than the other glands. After a feed the rate of protein synthesis in parotid glands was approximately double that of controls whilst that of the submandibular glands had increased by 24% and the sublingual glands remained unchanged. Acute ethanol injection led to a reduced rate of protein synthesis in all glands. The higher rate of protein synthesis in sublingual glands under fasting conditions may be related to the spontaneous secretion of fluid and protein from this gland, which would require a constant replenishment of secretory protein by synthesis. Protein synthesis in the parotid gland, like secretion, appears to be closely linked with the reflex stimulation caused by mastication. The smaller increase in rate of protein synthesis seen in the submandibular gland after a re-feed does not appear to have been recorded before. It could be mediated by the increased reflex stimuli caused by mastication or by some circulating factor. The mechanism by which ethanol reduces protein synthesis in all glands is uncertain.

Effects of surgical ovariectomy on rat salivary gland function

Studies sought to determine whether there are specific changes in salivary gland protein synthesis and secretion in response to hormone deficiency caused by ovariectomy of female rats. After 50 days, the wet weights of the parotid and submandibular glands did not change with hormone loss while that of the sublingual gland increased by 26% when compared to sham-operated controls. Amylase activity in the parotid declined, as did the level of enzyme activity present in saliva. The amount of the acidic proline-rich protein in the parotid was not altered after ovariectomy when compared to control sham-operated animals, using constant quantities of lysate protein. The total of secreted protein per unit volume did not change with ovariectomy. However, sodium dodecylsulphate-polyacrylamide gel electrophoresis of whole saliva showed the loss of a substantial number of proteins, including amylase and the acidic proline-rich proteins, from the experimental group. Epidermal growth factor concentrations were not significantly altered in the submandibular gland, while again showing a decrease in the concentration from saliva in ovariectomized rats.

Evidence for a juvenile hormone receptor involved in protein synthesis in Drosophila melanogaster.

The larval fat body of newly eclosed adults of Drosophila melanogaster was found to contain a single major binding protein specific for juvenile hormone (JH). Binding to this protein was saturable, of high affinity, and specific for JH III. The protein has a subunit molecular weight (Mr) of 85,000, as determined by photoaffinity labeling. The same or similar JH-binding protein was found in larval fat body and cuticle of third instar larvae and in male accessory glands and heads of newly eclosed adults. It was not found in several other tissues in adults. Male accessory gland cytosol from wild-type flies was found to contain a single binder with a dissociation constant (KD) of 6.7 nM for JH III; a binder in similar preparations from the methoprene-tolerant (Met) mutant had a KD value 6-fold higher. JH III stimulated protein synthesis in glands cultured in vitro, but this effect was reduced in Met flies as compared to wild-type flies, establishing a correlation between JH binding and biological activity of the hormone. In addition, glandular protein accumulation during the first 2 days of adult development was less in Met flies than in wild-type flies. These results strongly suggest that the binding protein we have identified mediates this JH effect in male accessory glands and thus is acting as a JH receptor.

Corpus allatum and corpus cardiacu regulation of long hyaline gland protein synthesis in the male grasshopper, Melanoplus sanguinipes

Rates of accumulation of, and radiolabel incorporation into, the major secretory product of the long hyaline gland, a glycoprotein LHPI, were used to examine the role of the corpus allatum (CA) and corpus cardiacum (CC) in the regulation of protein synthesis in the accessory reproductive gland of the male grasshopper, Melanoplus sanguinipes. Incorporation of [ 35S]methionine into LHPI in vitro indicated that LHPI was an endogenous long hyaline gland protein, whose in vivo synthesis in allatectomized animals was stimulated by topical application of juvenile hormone (JH) III. This response was not dependent on the presence of the extrinsic lobe of the CC, the CC/brain complex, or on continued feeding and suggests a direct effect of JH on the gland. Severance of the nervi corporis allati I and II reduced accumulation of LHPI but unilateral CA removal did not, perhaps because of a compensatory activation of the remaining CA. Normal postcopulatory stimulation of LHPI accumulation was abolished by allatectomy. These results suggest that the physiological level of JH may regulate LHPI synthesis. Corpus cardiacum effects were small in comparison to those of the CA; they were evident only in cardiacectomized animals that were allatectomized also and exerted over prolonged periods when the animals continued to feed. Endocrine manipulations produced no qualitative changes in long hyaline gland LHPI immunoreactive protein, only quantitative ones.

Juvenile hormone action mediated in male accessory glands of Drosophila by calcium and kinase C.

In an in vitro system for the Drosophila melanogaster male accessory gland, it was found that 10(-9)M juvenile hormone III could accurately mimic the copulation-induced response of increased protein synthesis in glands from virgin flies. Stimulation by this hormone required calcium in the medium. Experiments with tumor-promoting phorbol esters indicated that activation of protein kinase C can also cause the glands to increase protein synthesis. Stimulation of protein synthesis by juvenile hormone did not occur in mutants deficient in kinase C activity. These results suggest a membrane-protein-mediated effect of juvenile hormone that involves calcium and kinase C.

The Effect of Dietary Protein Quality and Feeding Level on Milk Secretion and Mammary Protein Synthesis in the Rat

Protein synthesis was studied in mammary tissue of rats fed diets deficient in protein quality and/or restricted in food intake throughout gestation and lactation. Diets containing 25% wheat gluten (WG), wheat gluten plus lysine and threonine (WGLT), or casein (C) were pair-fed from conception until day 15 of lactation at 100% or 85% of WG ad libitum consumption (PF100 and PF85, respectively). A seventh group was fed C ad libitum. Rates of protein synthesis were measured in vivo at day 15 of lactation from incorporation of [3-3H]phenylalanine. At both PF100 and PF85, fractional and absolute rates of mammary gland protein synthesis were two- to three-fold higher in rats fed C than in those fed WG. Pup weights showed similar treatment effects. Both mammary protein synthesis rates and pup weights were significantly higher in rats fed C at PF85 than rats fed WG ad libitum. Food restriction from PF100 to PF85 depressed pup weights and mammary protein synthesis rates in rats fed WGLT, but had no effect in rats fed WG. These results demonstrate that when food intake is restricted, improvement of protein quality of the maternal diet increases milk output in the rat in association with increased rates of mammary protein synthesis.

The Effect of Dietary Protein Quality and Feeding Level on Milk Secretion and Mammary Protein Synthesis in the Rat

Protein synthesis was studied in mammary tissue of rats fed diets deficient in protein quality and/or restricted in food intake throughout gestation and lactation. Diets containing 25% wheat gluten (WG), wheat gluten plus lysine and threonine (WGLT), or casein (C) were pair‐fed from conception until day 15 of lactation at 100% or 85% of WG ad libitum consumption (PF100 and PF85, respectively). A seventh group was fed C ad libitum. Rates of protein synthesis were measured in vivo at day 15 of lactation from incorporation of [3‐3H]phenylalanine. At both PF100 and PF85, fractional and absolute rates of mammary gland protein synthesis were two‐ to three‐fold higher in rats fed C than in those fed WG. Pup weights showed similar treatment effects. Both mammary protein synthesis rates and pup weights were significantly higher in rats fed C at PF85 than rats fed WG ad libitum. Food restriction from PF100 to PF85 depressed pup weights and mammary protein synthesis rates in rats fed WGLT, but had no effect in rats fed WG. These results demonstrate that when food intake is restricted, improvement of protein quality of the maternal diet increases milk output in the rat in association with increased rates of mammary protein synthesis.

Neuroendocrine stimulation of uterine gland protein synthesis in the tsetse fly, Glossina morsitans

ABSTRACT. The uterine gland of the tsetse fly Glossina morsitans morsitans Westw. synthesizes a secretion which nourishes the developing larva in the uterus. Aqueous extracts of the brain have been shown to stimulate the synthesis of the protein and amino acid components of this secretion from L‐ [U‐14C]leucine by uterine gland tubules in vivo and in vitro. A linear dose response relationship was demonstrated in vitro with extract concentrations ranging from 1 × 10‐4 to 1 × 10‐2 brains μl‐1. The maximum response, a &gt; 300% increase in the rate of protein and amino acid synthesis, was achieved with as little as 1 × 10‐2 brains μl‐1 The concentration of active factor(s) in the brain declined during a single interlarval period coincident with the period of release of secretion associated with larval growth. The stimulatory activity in brain extracts was destroyed by proteolytic enzymes indicating that it is probably a protein or peptide. Results suggest that the active factor(s) is a hormone responsible for the stimulation of uterine gland protein synthesis essential for larval nutrition.

Protein synthesis during salivary gland development, ageing, and cell death in Chironomus tentans larvae

Salivary gland protein synthesis in Chironomus tentans larvae was analyzed from the mid-third instar to larval pupation. Correcting for stage specific variations in the specific activity of the amino acid pool revealed a 30–40% reduction in the rate of protein synthesis during the larval moult. Except for a transient increase early in the fourth instar, this low rate of protein synthesis was maintained until the pharate pupal period when protein synthesis dramatically increased: maximum synthesis occurred in mid-pharate pupae with a subsequent decline correlating with gland autolysis and cell death at pupation. Each developmental period was characterized by a particular pattern of secretory protein synthesis: high and 35,000 daltons peptides were maximally synthesized only at particular larval stages, being reduced or absent in post-ecdysis, diapause and autolysing salivary glands. Except for the ecdysone puffs, and as otherwise previously noted ( Clever, 1961, 1962), puffing activity during the peri-moult period remained relatively constant and did not decrease by the 30–40% predicted from the decreased rate of protein synthesis. The nearly complete loss in synthesis of the 35,000 daltons peptide was not accompanied by regression in any puff.

Protein synthesis in pineal gland during serotonin- N-acetyltransferase induction

Protein synthesis in the cultured rat pineal gland was monitored during the course of N-acetyltransferase induction by ( l-isoproterenol or dibutyryl cyclic AMP. The incorporation of labeled amino acids into gland protein was essentially linear over a 6-h experimental period. Examination of the newly synthesized proteins by polyacrylamide gel electrophoresis and autoradiography did not reveal the appearance nor the disappearance of any specific protein(s) caused by ( l-isoproterenol or ( l)-propranolol. The lack of stimulation of synthesis of any specific protein was further demonstrated by constant ratio of incorporation in double-label experiments. Either 2μ m ( l)-isoproterenol or 1 m m dibutyryl cyclic AMP stimulated protein synthesis 20–40%. This increase was not due to an enhanced uptake of precursor radiolabeled amino acids by the glands when incubated with the β-agonist or cyclic AMP derivative. The stimulation of protein synthesis caused by ( l)-isoproterenol was abolished by the β-antagonist ( l)-propranolol. These results suggest that β-agonists may increase pineal gland protein synthesis through their relevant receptor and the generation of cyclic AMP. This increase in synthesis appears to be general and no selective elevation increase in any one band was observed.

Change in Size Distribution of Active Polyribosomes Associated with Puff Induction in Drosophila melanogaster Salivary Glands

The polytene cells of Drosophila melanogaster larvae are ideally suited for the study of gene information flow during differentiation, in that gene derepression is visualized in the form of chromosomal modifications called puffs. One special group of temperature-sensitive puffs can be experimentally induced within 5 min after transfer of salivary glands from 24-37 degrees C. Glands at 37 degrees C also begin synthesizing several new polypeptides which are of higher molecular weight than the prominent polypeptides being synthesized in glands at 24 degrees C [1]. The present study demonstrates that there is also a shift toward the utilization of heavier or more rapidly sedimenting polyribosomes for protein synthesis in glands transferred from 24-37 degrees C. As a result of such studies it is reasonable to assume that the polyribosome redistribution after a heat shock results from the translation of larger mRNA molecules synthesized by the temperature-sensitive loci. Further studies are suggested to describe the role of heat-induced gene activity in maintaining homeostasis, as well as the manner by which such activity is induced, in cells subjected to dramatic temperature fluctuations.

Regulation of submandibular salivary gland protein synthesis in the developing rat. The effect of food deprivation on polysome isolation and amino acid incorporation

It has been previously observed that RNase and RNase inhibitor have peak activities in the submandibular salivary gland of rats about 10 days old. This is the time when food deprivation seemed to be most effective in controlling levels of RNase through regulation of its inhibitor. Both linear sucrose density gradient analysis of polyribosomes and an in vitro amino acid incorporation system were used to support the hypothesis that a specific developmental period exists during which the protein synthetic capability of the submandibular salivary gland of the rat is at least partially controlled by diet.

Requirements of ribonucleic acid synthesis for the formation of salivary gland specific proteins in larval Chironomus tentans

Chromosomal ribonucleic acid synthesis in salivary gland cells of fourth instar Chironomus tentans larvae can be inhibited for 12–24 h with actinomycin D with no apparent effect on either the synthesis or the secretion of characteristic salivary gland proteins. Uptake, transport across the gland, and secretion of serum albumin are also relatively insensitive to inhibition by actinomycin D, but these processes are also unaffected when salivary gland protein synthesis is blocked with puromycin. The proteins characteristic of the differentiated state of the larval salivary gland appear to be synthesized on relatively stable ribonucleic acid templates, but new ribonucleic acid synthesis is required for further development.