Synthesis and turnover of hdRNA and mRNA in the salivary gland of the blowfly Calliphora erythrocephala.

We have measured the absolute molar rates of synthesis, accumulation, and turnover of blowfly salivary gland heterodisperse RNA. Twelve- and 84-hr-stage third-instar Calliphora erythrocephala larvae were injected with [³H]adenosine, and its flow into glandular ATP, heterodisperse RNA, and polyadenylated RNA was each quantitated over a 360-min time course. The results of these experiments indicate that at least 80% of the newly synthesized heterodisperse RNA mass is a >28 S nuclear species whose average first-order half-life is approximately 20 min. The remaining 20% of the heterodisperse RNA has a 6–28 S size distribution, accumulates in the cytoplasm, and is associated with functional polysomes. The average first-order half-life of this more stable species is 20–25 hr. In addition, we have independently quantitated by optical methods the developmental change in the content of polysome-associated mRNA. The mRNA in these studies also has an average first-order half-life of 25 hr and accounts for 25–55% of the mRNA mass predicted by the incorporation-kinetic analysis of the pulse-labeled heterodisperse RNA. Despite the increased polyteny of the older stage glands, the rates of synthesis and accumulation of each of the individual heterodisperse RNA classes are the same at the 12- and 84-hr stages. Collectively, these results demonstrate that salivary gland functional specialization results from the accumulation of long-lived mRNA and not from changes in the overall rate of mRNA synthesis.     

Salivary gland development in the blowfly,Calliphora erythrocephala

The salivary gland of adult Calliphora erythrocephala is a tubular structure composed of secretory, reabsorptive, and duct regions. Development of these structures has been followed during the six days of larval and ten days of pupal growth. Two small groups of imaginal cells located at the junction between larval gland and duct give rise to the adult gland. These presumptive adult cells divide during all larval stages and appear to be functional components of the larval gland. Shortly after pupation, the larval gland breaks down and the imaginal cells proliferate rapidly, forming sequentially the duct, reabsorptive and secretory regions. Proliferating regions of the developing gland are frequently encrusted with haemocytes. As it elongates the gland establishes intimate contacts first with the basement membrane of the degenerating larval gland, later with an epithelial layer surrounding the main dorsal tracheal trunks, and then with the gut. Cell division continues until about five days after pupation, bu t the gland is unable to secrete fluid in response to 5-hydroxytryptamine stimulation until two hours after the adult fly emerges. The Golgi complex appears to be involved in forming the highly folded membranes of the canaliculi in the secretory region. Presumptive adult salivary gland cells appear to increase in number logarithmically from the time of hatching of the larva until five days after pupation. This contrasts with the development of classical imaginal discs, in which cell division ceases prior to pupation.     

The ultrastructure of developing wings in the giant silkmoth, Hyalophora cecropia. I. Generalized epidermal cells

The ultrastructure of wing epidermis of the giant silkmoth, Hyalophora cecropia, was studied during pupal diapause and the first half of development to the adult. In diapause, the generalized epidermal cells are characterized by many free ribosomes, some vesicles and small lamellae of rough endoplasmic reticulum, some scattered short mitochondria and a few small Golgi complexes. During the early states of post-diapause development, before and after the time of apolysis (separation of the epidermis from the overlying cuticle), there is a marked increase in structures often associated with synthetic functions, such as polyribosomes, lamellate rough endoplasmic reticulum and Golgi complexes. On day five of post-apolysis development, just after the appearance of scale-forming and socket-forming cells, the generalized epidermal cells lay down the cuticulin layer of the adult cuticle. At this stage and later, the polyribosomes and lamellate rough endoplasmic reticulum decrease in abundance. Cell nuclei show three phases of temporary transition from predominantly lobed to predominantly round profile, which correspond to periods of reported DNA synthesis. Throughout this developmental process, therefore, there is good correlation of fine structure with changes in macromolecular synthesis recorded elsewhere.     

Balbiani ring RNA in the cytoplasm of Chironomus thummi salivary gland cells

In this paper experimental results on the size, transport and stability of cytoplasmic Balbiani ring RNA and on its appearance in polysomes are presented. Cytoplasmic RNA of salivary gland cells from Chironomus thummi contains two large RNA fractions of about 20×10⁶ dalton and 10×10⁶ dalton in size. These RNA fractions correspond both to Balbiani ring BR 1 RNA and BR 2 RNA and are apparently transported from nucleus into cytoplasm without a significant size reduction. Chase experiments illustrate a great stability of giant cytoplasmic Balbiani ring RNA molecules and exclude the possibility of a precursor-product relationship between these and smaller BR RNA molecules also found in cytoplasm. A part of giant cytoplasmic Balbiani ring RNA molecules is bound to poly(U)-sepharose columns and should, therefore, contain poly(A)-sequences. — Polysomes of salivary gland cells extracted by a gentle lysis procedure and centrifuged through sucrose gradients are characterized by a rather broad sedimentation profile. Polysome sizes up to about 800 S have been detected, but in no case a distinct polysome fraction corresponding in size to Balbiani ring RNA has been observed. Hybridization of polysomal RNA with salivary gland chromosomes in situ resulted in labelling of both Balbiani rings BR 1 and BR 2.     

Premetamorphic changes in the ultrastructure of Calliphora fat cells

Summary In the fat body of Calliphora a drastic reorganization of the cell structure, which is related to premetamorphic functional changes, can be observed during the 3rd larval stage of development. These changes include an accumulation of protein storage granules, a decrease in the relative volume of the mitochondria and the surface area of endoplasmic reticulum membrane, and the disappearance of vacuoles. Absolute values obtained for organelle areas and membrane perimeters confirm the assumption that large numbers of organelles are eliminated by autophagic activity prior to the pupation period. A temporary restoration of the endoplasmic reticulum is found immediately before pupariation. Large variations in organelle density were found between individual fat cells and between the nuclear, mid- and peripheral regions of the cytoplasm.     

RNA synthesis in a Balbiani ring in Chironomus tentans salivary gland cells

Rapidly labelled RNA in Balbiani ring 2 on chromosome IV in the salivary glands of Chironomus tentans was investigated. This RNA is likely to be transcribed from only one chromosomal band, supposed to be a single operational unit in these polytenic cells (Beermann, 1966).Salivary glands were incubated in larval haemolymph, supplemented with tritiated RNA precursors and fixed afterwards. Balbiani rings 2 (in some experiments also Balbiani ring 1 and 3) were isolated with micromanipulation. The labelled RNA was extracted with SDS-pronase and analysed with electrophoresis in agarose.The rapidly labelled RNA in Balbiani ring 2 was as heterogeneous as RNA from the remainder of the chromosome set (10–90 S) but the peak of the distribution of label in BR 2 corresponded to molecules of about 50 S as compared to that of RNA from the rest of the chromosome set which was about 35 S. When the synthetic activity in Balbiani ring 2 was very high, relatively more molecules with very high molecular weights were produced compared with the state when the synthetic activity was moderate or low. The synthetic activity in Balbiani ring 2 compared to that in Balbiani ring 1 was well correlated to the relative sizes of the two Balbiani rings. The results on Balbiani ring 2 are discussed in relation to the size and structure of the chromomere.     

5-Hydroxytryptamine immunoreactivity in the epidermal sacciform gland cells of the clingfish Lepadogaster candollei Risso

Summary Serotonin has been demonstrated in the epidermal sacciform glandular cells of the clingfish Lepadogaster candollei by use of immunocytochemistry.Serotonin immunoreactivity is found both in the peripheral cytoplasm of the glandular cells and their luminal secretion. The presence of serotonin in the sacciform glandular cells parallels that located by both biochemical and immunocytochemical procedures in the cutaneous glands of many amphibian species.     

Possible physiological role of epidermal growth factor in the development of the mouse mammary gland during pregnancy

Epidermal growth factor stimulated cell proliferation in a primary mammary epithelial cell culture derived from mice at different stages of pregnancy. Moreover, the peptide hormone inhibited casein production induced by the synergistic actions of insulin, cortisol and prolactin. The inhibitory effect of epidermal growth factor was influenced by the gestational stages of the mammary gland. These effects of epidermal growth factor were exerted at physiological concentrations. The dual actions of epidermal growth factor on mammary cells implicate its participation in regulation of the growth and differentiation of the mammary gland during pregnancy.     

Occurrence of gastrin-releasing peptide-like and bombesin-like immunoreactivities in the epidermal sacciform gland cells of the clingfish Lepadogaster candollei

Gastrin-releasing peptide (GRP)-like and bombesin (BOM)-like immunoreactivities were localized in the exocrine sacciform gland cells and in the surface epidermis of the clingfish Lepadogaster candollei with the use of previously characterized antibodies. The GRP-like and BOM-like peptides show resemblance to those immunohistochemically found in the dermal secretory products of the amphibian skin. The immunoreactive peptides tested in this study are unusual bioactive components of secretory sources of exocrine glands since these peptides were first demonstrated in cells of the neuroendocrine system. The results suggest that such bioactive compounds may exert regulatory activity in the absorptive processes of the skin epithelium and in influencing secretion release from exocrine complexes.     

Role of macrophages and multinucleate giant cells in the resorption of corpora amylacea in the involuting bovine mammary gland

Summary Microscopic examination of involuting bovine mammary tissue revealed elevated concentrations of corpora amylacea in alveolar lumina. Morphologic relationships between amyloid bodies, macrophages, and multinucleate giant cells (MGCs) suggested phagocytosis and degradation of the deposits by the phagocytic cells. Resorption of amyloid material by macrophages and MGCs during the process of mammary involution may be instrumental in preventing accumulation of corpora amylacea in secretory tissue which may interfere with mechanisms of milk synthesis and secretion.     

Balbiani ring RNA content and half-life in nucleus and cytoplasm of Chironomus tentans salivary gland cells

The content of RNA with an origin in the Balbiani rings 1 and 2 (BR 1+2) has been determined in chromosomes, nuclear sap and cytoplasm of Chironomus tentans salivary gland cells. Together with information on rate and completeness of export this permits an estimation of half-life of this RNA in cytoplasm and its residence time in the nucleus. The quantities in the BR, nuclear sap, and cytoplasm are roughly related as 110200. The 75 S RNA in the nuclear sap with an origin in the BR 1+2 must to a high extent be a precursor to the cytoplasmic 75 S RNA in vivo. The half-life of the cytoplasmic component is about 20 h and the half-life (residence time) for BR 1+2 RNA in the nuclear sap around one hour. The presence of a large pool of BR RNA in the sap explains the previously observed delay in its cytoplasmic appearance in vivo.     

Isolation and characterization of the two giant secretory proteins in salivary gland of Chironomus tentans.

The two giant secretory proteins, sp-Ia and sp-Ib, in salivary-gland cells of the larva of the fly Chironomus tentans, were isolated by preparative gel electrophoresis and characterized chemically. Their amino acid compositions are dominated by polar amino acids, with about 30% of basic amino acid residues. Crossed immunoelectrophoresis of sp-Ia and sp-Ib provided evidence that they share antigenic determinants. They also have major methionine-containing tryptic peptides in common. CNBr cleavage of sp-Ib gives a small number of low-Mr fragments, indicating that this protein has a repetitive structure.     

Optical properties of the ocelli of Calliphora erythrocephala and their role in the dorsal light response

The 3 ocelli of the blowfly Calliphora erythrocephala, grouped close together on the top of the head (Fig. 1), have large, extensively overlapping visual fields. Together they view the entire upper hemisphere of the surroundings plus part of the lower hemisphere (Figs. 5, 7). It is shown for the lateral ocelli that despite the underfocussing of the ocellar lens large patterns are imaged on the receptor mosaic. Because of the astigmatism of the lens, patterns in longitudinal orientations are more accurately represented than in others (Fig. 3). Nevertheless, an artifical horizon rotated around the long axis of the animal does not elicit head roll. Likewise, changes of overall brightness in the visual field of the median and one lateral ocellus elicit only weak phasic-tonic dorsal light responses of the animal which supplement the tonic dorsal light responses mediated by the compound eyes (Figs. 9, 10). Our results show that, in Calliphora, the ocelli have little influence on head orientation during flight, and must be assumed to serve other functions.Abbreviations body pitch angle - head-tilt angle - DNOVS descending neuron of the ocellar and vertical cell systems - HR head roll - spatial wavelength - R roll angle - SD standard deviation