Radioautographic study of in vivo and in vitro incorporation of fucose-3H into thyroglobulin by rat thyroid follicular cells

Spam1-associated transmission ratio distortion in mice: elucidating the mechanism

BACKGROUND

While transmission ratio distortion, TRD, (a deviation from Mendelian ratio) is extensive in humans and well-documented in mice, the underlying mechanisms are unknown. Our earlier studies on carriers of spontaneous mutations of mouse Sperm Adhesion Molecule 1 (Spam1) suggested that TRD results from biochemically different sperm, due to a lack of transcript sharing through the intercellular cytoplasmic bridges of spermatids. These bridges usually allow transcript sharing among genetically different spermatids which develop into biochemically and functionally equivalent sperm.

OBJECTIVES

The goals of the study were to provide support for the lack of sharing (LOS) hypothesis, using transgene and null carriers of Spam1, and to determine the mechanism of Spam1-associated TRD.

METHODS

Carriers of Spam1-Hyal5 BAC transgenes were mated with wild-type female mice and the progeny analyzed for TRD by PCR genotyping. Sperm from transgene and Spam1 null carriers were analyzed using flow cytometry and immunocytochemistry to detect quantities of Spam1 and/or Hyal5. Transgene-bearing sperm with Spam1 overexpression were detected by fluorescence in situ hybridization. In wild-type animals, EM studies of in situ transcript hybridization of testis sections and Northern analysis of biochemically fractionated testicular RNA were performed to localize Spam1 transcript. Finally, AU-rich motifs identified in the 3' UTR of Spam1 RNA were assayed by UV cross-linking to determine their ability to interact with testicular RNA binding proteins.

RESULTS

The Tg8 line of transgene carriers had a significant (P < 0.001) TRD, due to reduced fertilizing ability of transgene-bearing sperm. These sperm retained large cytoplasmic droplets engorged with overexpressed Spam1 or Hyal5 protein. Caudal sperm from transgene carriers and caput sperm of null carriers showed a bimodal distribution of Spam1, indicating that the sperm in a male were biochemically different with respect to Spam1 quantities. Spam1 RNA was absent from the bridges, associated exclusively with the ER, and was shown to be anchored to the cytoskeleton. This compartmentalization of the transcript, mediated by cytoskeletal binding, occurs via protein interactions with 3' UTR AU-rich sequences that are likely involved in its stabilization.

CONCLUSION

We provide strong support for the LOS hypothesis, and have elucidated the mechanism of Spam1-associated TRD.

Cytoplasmic localization during testicular biogenesis of the murine mRNA for Spam1 (PH-20), a protein involved in acrosomal exocytosis

The Sperm Adhesion Molecule1 (SPAM1) is the most widely conserved sperm antigen with important roles in mammalian fertilization. Light and electron microscopy were used to localize, by in situ hybridization, the cellular and subcellular sites of Spam1 mRNA in the murine testis. Transcripts were first detected in step 3 round spermatids, gradually increased until step 8 and abruptly decreased between steps 9-11. They were predominantly localized near the ER and were not dispersed throughout the cytoplasm. Immunohistochemistry revealed that Spam1 is present on both the head and tail of sperm in the seminiferous tubules, and provided support for transcriptional regulation of its transcript. Immunocytochemistry confirmed the location of Spam1 on the tail of testicular sperm and demonstrated that it is localized to both the principal piece and the midpiece. Spam1 on epididymal sperm is localized to the midpiece of the tail and changes from a uniform distribution on the head in the caput to a regionalized pattern, first on the posterior and then on the anterior head, in caudal sperm. Spam1 on the surface of caudal sperm was shown to mediate the increase in acrosome reactions induced by the synergistic effects of HA and progesterone, as confirmed in sperm from the Rb(6.16) translocation-bearing mice which are Spam1 mutants. The similar response of human and mouse sperm to these agonists of the acrosome reaction, underscores the usefulness of the mouse as a model to study physiological aspects of SPAM1 in humans where, unlike the mouse, it is the only sperm hyaluronidase.

The kinesin KIF17b and RNA-binding protein TB-RBP transport specific cAMP-responsive element modulator-regulated mRNAs in male germ cells

Testis brain RNA-binding protein (TB-RBP), the mouse orthologue of the human protein Translin, is a widely expressed and highly conserved protein with proposed functions in chromosomal translocations, mitotic cell division, and mRNA transport, stabilization, and storage. Targeted inactivation of TB-RBP leads to abnormalities in fertility and behavior. A testis-enriched kinesin KIF17b coimmunoprecipitates with TB-RBP in a RNA-protein complex containing specific cAMP-responsive element modulator (CREM)-regulated mRNAs. The specificity of this interaction is confirmed by in vivo RNA-protein crosslinking and transfections of hippocampal neurons. Combining in situ hybridization and immunohistochemistry at the electron microscope level, a temporally sequential dissociation of KIF17b and TB-RBP from specific mRNAs is detected with TB-RBP release coincident with the time of mRNA translation, indicating a separation of the processes of transport and translation. We conclude that KIF17b serves as a molecular motor component of a TB-RBP-mouse ribonucleoprotein complex transporting a group of specific CREM-regulated mRNAs in mammalian male postmeiotic germ cells. Because KIF17b has been reported to control CREM-dependent transcription in male germ cells by regulating the intracellular location of the transcriptional coactivator activator of CREM in testis, this indicates that one kinesin links the processes of transcription and transport of specific mRNAs in mammalian male germ cells.

A TB-RBP and Ter ATPase complex accompanies specific mRNAs from nuclei through the nuclear pores and into intercellular bridges in mouse male germ cells

The testis brain RNA-binding protein (TB-RBP) functions as an RNA-binding protein in brain and testis, binding to conserved sequence elements present in specific mRNAs, such as protamine 1 and 2. We show here by RNA gel shift assays, immunoprecipitation, and by a novel in situ hybridization immunohistochemical technique that TB-RBP binds to AKAP4 mRNA in male mouse germ cells. AKAP4 is a component of the fibrous sheath and functions as a scaffolding protein in the sperm flagellum. AKAP4 is encoded by an X-linked gene, is expressed solely in postmeiotic (haploid) male germ cells, and is an essential protein in all spermatozoa, requiring its transport between spermatids as a protein or mRNA. AKAP4 mRNA forms a complex with TB-RBP and the Ter ATPase in nuclei and remains associated with these proteins as it exits nuclei into the cytoplasm and as it passes through intercellular bridges between spermatids. A similar mRNA-TB-RBP-Ter ATPase association is seen for protamine 2 mRNA, which is stored in the cytoplasm of postmeiotic germ cells about 7 days before translation. In contrast, no association is seen with PGK-2 mRNA which is initially transcribed early in meiosis with increased transcription in postmeiotic male germ cells. Although PGK-2 mRNA is subject to translational control, it lacks TB-RBP-binding sequences in its mRNA. The AKAP4 or protamine 2 mRNA-protein complexes dissociate in late-stage male germ cells when the mRNAs are translated. We propose that TB-RBP and the Ter ATPase are part of a complex that accompanies specific mRNAs in haploid mouse male germ cells in intracellular and intercellular movement. The temporal relationship of TB-RBP binding and mRNA inactivation in conjunction with the subsequent dissociation of the mRNA-protein complex at the time of mRNA translation suggests a role in translational suppression and/or mRNA stabilization.

Radioactive fucose as a tool for studying glycoprotein secretion

The efficiency and reliability of radioactive fucose as a specific label for newly synthesized glycoproteins were investigated. Young adult male rabbits were injected intravitreally with [3H]-fucose, [3H]-galactose. [3H]-mannose, N-acetyl-[3H]-glucosamine or N-acetyl-[3H]-mannosamine, and killed 40 h after injection. In another series of experiments rabbits were injected with either [3H]-fucose or several tritiated amino acids and the specific activity of the vitreous proteins was determined. Vitreous samples were also processed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and histological sections of retina, ciliary body and lens (the eye components around the vitreous body) were processed for radioautography. The specific activity (counts per minute per microgram of protein) of the glycoproteins labeled with [3H]-fucose was always much higher than that of the proteins labeled with any of the other monosaccharides or any of the amino acids. There was a good correlation between the specific activity of the proteins labeled by any of the above precursors and the density of the vitreous protein bands detected by fluorography. This was also true for the silver grain density on the radioautographs of the histological sections of retina, ciliary body and lens. The contribution of radioautography (after [3H]-fucose administration) to the elucidation of the biogenesis of lysosomal and membrane glycoproteins and to the determination of the intracellular process of protein secretion was reviewed. Radioactive fucose is the precursor of choice for studying glycoprotein secretion because it is specific, efficient and practical for this purpose.

Collagen gel-embedding culture of conjunctival epithelial cells

BACKGROUND

Collagen has effects on cell morphology, differentiation characteristics and function. Using collagen gel culture, several studies about cell differentiation were reported. In this study, the differentiation of rabbit conjunctival epithelial cells in a collagen gel-embedding culture system was investigated by electron microscope and lectin labeling.

METHODS

Rabbit bulbar conjunctival epithelial cells were cultured in type I collagen gel. After 1 and 2 weeks of culture, some of these cells were stained with PAS and seven kinds of lectins, and others were examined by transmission electron microscopy.

RESULTS

The conjunctival epithelial cells cultured within collagen gel formed stratified cell layers and globules with cavities. The inner layer cells facing the cavities showed PAS and lectin staining patterns similar to those of conjunctival goblet cells in vivo, whereas the staining patterns of the outer layer cells on the collagen matrices resembled the patterns of non-goblet epithelial cells. Microvilli on the surface of the innermost cells, basement membranes beneath the outermost cells, tight junctions, adherent junctions, interdigitating folds and desmosomes between cells were identified on electron microscopic examination.

CONCLUSION

These results indicate that cell junction structures of the conjunctival epithelial cells are well developed in collagen gel-embedding culture systems, and that the inner layer cells have carbohydrates similar to those of conjunctival goblet cells. Culture of conjunctival epithelial cells within collagen gel is a useful model for examining differentiation of these cells.

The juxtatesticular body of jawfishes (Teleostei, Opistognathidae): Comparative morphology and fine structure

A peculiar gland, the juxtatesticular body (JTB), ductless and consisting of follicles, had previously been discovered in males of two Opistognathus species (Teleostei, Opistognathidae). In this paper, we describe (1) the general morphology of the JTB in an additional two Opistognathus species, O. aurifrons and O. macrognathus, comparing it with that of the previously described species, and (2) the fine structure of the JTB of Opistognathus whitehurstii and O. maxillosus. Interspecific variability occurs both in the general organization of this gland and in the number of follicular cells. Fine structural analysis of the JTB, both in O. whitehurstii and O. maxillosus, reveals strong similarities with thyroid follicular cells, suggesting a similar pattern of synthesis and secretion. JTB follicular cells are arranged as a monolayered epithelium that surrounds a follicular lumen; they show a polarity in organelle distribution and membrane specialization typical of secreting cells. On the basis of their cytological and histochemical characteristics we propose that JTB follicular cells perform two major types of secretory activities: the secretion of a glycoprotein from the apical part of the cells into the follicular lumen and the endocrine, or paracrine, secretion of a still unknown substance(s) from the basal part of the cell either into the extrafollicular space or the blood or both. A hypothesis concerning the functional cycle of JTB follicle is also discussed. © 1995 Wiley-Liss, Inc.

Histochemical demonstration of acid phosphatase activity in terminal Schwann cells associated with Ruffini endings in the periodontal ligament of rat incisors

Histochemical staining for acid phosphatase, a marker for lysosomal elements, distinguished rounded, intensely reactive cells from less reactive fibroblasts and osteoblasts in the lingual periodontal ligament. The highly reactive cells were located exclusively in the alveolar half of the ligament. Double staining for acid phosphatase and S-100 protein confirmed that these reactive cells were identical with the terminal Schwann cells associated with periodontal Ruffini endings. Electron microscopically, reaction products for acid phosphatase were observed in the lysosomes and Golgi apparatus in the paranuclear cytoplasm of the terminal Schwann cells. As the terminal Schwann cells associated with the Ruffini endings are assumed to be capable of synthesizing exportable proteins, acid phosphatase in this type of cell may be involved in the processing of macromolecules in synthetic and/or secretory pathways.

Traffic through the Golgi apparatus as studied by radioautography

The ability to radiolabel biological molecules, in conjunction with radioautographic or cell fractionation techniques, has brought about a revolution in our knowledge of dynamic cellular processes. This has been particularly true since the 1940's, when isotopes such as 35S and 14C became available, since these isotopes could be incorporated into a great variety of biologically important compounds. The first dynamic evidence for Golgi apparatus involvement in biosynthesis came from light microscope radioautographic studies by Jennings and Florey in the 1950's, in which label was localized to the supranuclear Golgi region of goblet cells soon after injection of 35S-sulfate. When the low energy isotope tritium became available, and when radioautography could be extended to the electron microscope level, a great improvement in spatial resolution was achieved. Studies using 3H-amino acids revealed that proteins were synthesized in the rough endoplasmic reticulum, migrated to the Golgi apparatus, and thence to secretion granules, lysosomes, or the plasma membrane. The work of Neutra and Leblond in the 1960's using 3H-glucose provided dramatic evidence that the Golgi apparatus was involved in glycosylation. Work with 3H-mannose (a core sugar in N-linked side chains), showed that this sugar was incorporated into glycoproteins in the rough endoplasmic reticulum, providing the first radioautographic evidence that glycosylation of proteins did not occur solely in the Golgi apparatus. Studies with the tritiated precursors of fucose, galactose, and sialic acid, on the other hand, showed that these terminal sugars are mainly added in the Golgi apparatus. With its limited spatial resolution, radioautography cannot discriminate between label in adjacent Golgi saccules. Nonetheless, in some cell types, radioautographic evidence (along with cytochemical and cell fractionation data) has indicated that the Golgi is subcompartmentalized in terms of glycosylation, with galactose and sialic acid being added to glycoproteins only within the trans-Golgi compartment. In the last ten years, radioautographic tracing of radioiodinated plasma membrane molecules has indicated a substantial recycling of such molecules to the Golgi apparatus.

Regulated and constitutive protein targeting can be distinguished by secretory polarity in thyroid epithelial cells

We have studied concurrent apical/basolateral and regulated/constitutive secretory targeting in filter-grown thyroid epithelial monolayers in vitro, by following the exocytotic routes of two newly synthesized endogenous secretory proteins, thyroglobulin (Tg) and p500. Tg is a regulated secretory protein as indicated by its acute secretory response to secretagogues. Without stimulation, pulse-labeled Tg exhibits primarily two kinetically distinct routes: less than or equal to 80% is released in an apical secretory phase which is largely complete by 6-10 h, with most of the remaining Tg retained in intracellular storage from which delayed apical discharge is seen. The rapid export observed for most Tg is unlikely to be because of default secretion, since its apical polarity is preserved even during the period (less than or equal to 10 h) when p500 is released basolaterally by a constitutive pathway unresponsive to secretagogues. p500 also exhibits a second, kinetically distinct secretory route: at chase times greater than 10 h, a residual fraction (less than or equal to 8%) of p500 is secreted with an apical preponderance similar to that of Tg. It appears that this fraction of p500 has failed to be excluded from the regulated pathway, which has a predetermined apical polarity. From these data we hypothesize that a targeting hierarchy may exist in thyroid epithelial cells such that initial sorting to the regulated pathway may be a way of insuring apical surface delivery from one of two possible exocytotic routes originating in the immature storage compartment.

Study of the differentiation of secretory cells in the golden hamster oviductal epithelium by use of a monoclonal antibody

The ontogeny of an oviductal zona pellucida glycoprotein, designated ZP-0, in the golden hamster oviductal epithelium was investigated by means of light and electron microscopic immunolabeling studies using a monoclonal antibody. Light microscopic immunohistochemistry showed that ZP-0 appeared in the oviductal epithelium from 9.5 to 10.5 days after birth. At first, ZP-0 appeared in the Golgi region of the epithelial cells, and then increased in amount as development progressed to fill the supranuclear cytoplasm. Electron microscopic observations showed that rough endoplasmic reticulum and Golgi apparatus were well developed in non-ciliated cells of the ampullar and isthmic segments at 10.5 days after birth. Secretory granules appeared near the Golgi apparatus and markedly increased in number until 15.5 days after birth. Ultrastructural immunocytochemistry showed that ZP-0 appeared in the well-developed Golgi apparatus and then was stored within the secretory granules of developing secretory cells. ZP-0 was never present in the ciliated cells. These results indicate a coincidence between the beginning of ZP-0 biosynthesis and the morphological cytodifferentiation of secretory cells in the golden hamster oviduct during postnatal development. This leads us to the conclusion that ZP-0 is a possible differentiation marker of the golden hamster oviductal secretory cell.

Characterization of fucosyltransferase activity during mouse spermatogenesis: evidence for a cell surface fucosyltransferase

Fucosyltransferase activity was quantified in mouse germ cells at different stages of spermatogenesis. Specifically, fucosyltransferase activities of pachytene spermatocytes, round spermatids, and cauda epididymal sperm were compared. Fucosyltransferase activity of mixed germ cells displayed an apparent Vmax of 17 pmol (mg of protein)-1 min-1 and an apparent Km of approximately 13 microM for GDP-L-[14C]fucose in the presence of saturating amounts of asialofetuin at 33 degrees C. Under these conditions, cellular fucosyltransferase activity was found to increase during spermatogenesis. In agreement with assays of intact cells, examination of subcellular fractions indicated that a large fraction of fucosyltransferase activity was associated with the cell surface. The fraction of fucosyltransferase activity that was associated with the cell surface progressively increased throughout spermatogenesis and epididymal maturation so that nearly all of the fucosyltransferase in epididymal sperm was on the cell surface. Specifically, by comparison of activities in the presence and absence of the detergent NP-40, the fraction of fucosyltransferase activity that was associated with the cell surface in pachytene spermatocytes, round spermatids, and epididymal sperm was 0.36, 0.5, and 0.85, respectively. These results suggest that a cell surface fucosyltransferase may be important during differentiation of spermatogenic cells in the testis as well as during epididymal maturation and fertilization.

Budding of small vesicles from the rough-surfaced endoplasmic reticulum in secretory ameloblasts of rat molar tooth germs

The budding of small vesicles from the rough-surfaced endoplasmic reticulum (rER) was examined in the secretory ameloblast of rat molar tooth germs by ordinary fixation or prolonged osmium fixation. The budding of small vesicles from the rER was observed not only at the special region (transitional region) of the rER system, which abutted on the cis-face of the Golgi apparatus, but also at other regions of the rER in the secretory ameloblast. Small vesicles (presumed to be transitional vesicles) were adjacent to the rER, which also showed budding of vesicles. After prolonged osmium treatment, osmium deposits appeared in small vesicles, as well as in the cisternae of the cis saccule of the Golgi apparatus. Small vesicles containing osmium deposits were located at various regions of the cell, including the cis-face of the Golgi apparatus. These findings indicate that the budding of small vesicles from the rER is not restricted to the transitional region of the rER system of the secretory ameloblast, but is found at various regions of the cell. This indicates that newly synthesized proteins may be transferred from the rER cisternae to the transitional vesicles not only in the transitional region of the rER system adjacent to the Golgi apparatus, but also in other regions of the secretory ameloblast.

Phosphoprotein synthesis and secretion by odontoblasts in rat incisors as revealed by electron microscopic radioautography

The secretory pathway of dentin phosphoproteins in rat incisors was studied by electron microscopic radioautography after the injection of 3H-serine, and the results were compared with those using 3H-proline as a tracer. Five min after injection of 3H-serine, radioactivity was found in the rough endoplasmic reticulum. At 10 min, silver grains were observed over the spherical portions of the cisface of the Golgi apparatus. At 20 min after injection, silver grains were seen over the cylindrical portions of the transface of the Golgi apparatus. The secretory granules showed the strongest reaction from 20 min to 1 hr. At 45 min, a significant labeled band appeared at the mineralization front. At 1 hr, the labeling at the mineralization front began to appear in the mineralized dentin, and after 12 hr this labeled band was located within the mineralized dentin. The pathway of 3H-proline was essentially the same as that of 3H-serine, but 3H-proline moved more slowly than 3H-serine, especially in transit from the rough endoplasmic reticulum to the Golgi apparatus. Secretory granules were heavily labeled from 30 min to 1 hr after injection of 3H-proline; no labeling was found at the mineralization front at 45 min. The labeling seen initially over the predentin was over the mineralized dentin no earlier than 6 hr after injection. The labeling pattern with 3H-serine is closely related to the localization of phosphoproteins, whereas the pattern with 3H-proline reflects the production of collagen rather than of phosphoproteins. The present radioautographic results indicate that dentin phosphoproteins are related to secretory granules and are secreted by odontoblasts at the mineralization front and also that phosphoproteins are involved in the process of mineralization of the circumpulpal dentin.

Localization of the incorporation of 3H-galactose and 3H-sialic acid into thyroglobulin in relation to the block of intracellular transport induced by monensin. Studies with isolated porcine thyroid follicles

The Na+/K+ ionophore monensin is known to arrest the intracellular transport of newly synthesized proteins in the Golgi complex. In the present investigation the effect of monensin on the secretion of 3H-galactose-labeled and 3H-sialic acid-labeled thyroglobulin was studied in open thyroid follicles isolated from porcine thyroid tissue. Follicles were incubated with 3H-galactose at 20 degrees C for 1 h; at this temperature the labeled thyroglobulin remains in the labeling compartment (Ring et al. 1987a). The follicles were then chased at 37 degrees C for 1 h in the absence or presence of 1 microM monensin. Without monensin substantial amounts of labeled thyroglobulin were secreted into the medium, whereas in the presence of the ionophore secretion was inhibited by 80%. Since we have previously shown (Ring et al. 1987b) that monensin does not inhibit secretion of thyroglobulin present on the distal side of the monensin block we conclude that galactose is incorporated into thyroglobulin on the proximal side of this block. Secretion was also measured in follicles continuously incubated with 3H-galactose for 1 h at 37 degrees C in the absence or presence of monensin. In these experiments secretion of labeled thyroglobulin was inhibited by about 85% in the presence of monensin. Identically designed experiments with 3H-N-acetylmannosamine, a precursor of sialic acid, gave similar results, i.e., almost complete inhibition of secretion of labeled thyroglobulin in the presence of monensin. The agreement between the results of the galactose and sialic acid experiments indicates that sialic acid, like galactose, is incorporated into thyroglobulin on the proximal side of the monensin block.(ABSTRACT TRUNCATED AT 250 WORDS)

3H-mannose utilization by fibroblasts of the periodontal ligament

The synthesis, intracellular translocation, and secretion of mannose-containing glycoproteins(s) by periodontal ligament fibroblasts have been investigated by means of electron microscopic radioautography. Tritiated mannose was administered to young mice via jugular vein, and radioautographs were prepared at 5, 10, 20, and 35 minutes, 4 and 8 hours after injection. Analysis of electron microscopic radioautographs revealed a maximum labeling (94%) with 3H-mannose of the rough endoplasmic reticulum at 5 minutes. Labeling of the Golgi components started to increase from 10 minutes (14%) and reached a maximum level at 20 minutes (31.2%). At 35 minutes, secretion granules, dense bodies, profiles of intracellular collagen, and the cell surface were labeled. At 8 hours, most labelling (79.2%) was extracellular, and associated either with the collagenous matrix (43.7%) or the cell surface (35.5%). Cytoplasmic vesicles containing dense materials around collagen fibrils were also labeled at 8 hours. It is concluded that mannose is directly incorporated into the rough endoplasmic reticulum (RER), and that mannose-containing glycoprotein(s) are packaged in the Golgi apparatus into secretory granules. Mannose-containing glycoprotein(s) become distributed on the periodontal ligament (PDL) fibroblast cell surface, cytoplasmic dense bodies, and the extracellular matrix.

Synthesis and migration of 3H-fucose-labeled glycoproteins in the retinal pigment epithelium of albino rats, as visualized by radioautography

3H-fucose was injected into the vitreous body of the eye(s) of 250-gm rats, which were then killed by means of an intracardiac perfusion with glutaraldehyde after intervals of 10 min, 1 and 4 hr, and 1 and 7 days. The eyes were removed and further fixed, and pieces of retina were processed for light and electron microscope radioautography. Light microscope radioautography showed that the pigment epithelial cells actively incorporated 3H-fucose label. The intensity of reaction peaked at 4 hr after injection of the label and then slowly declined. Quantitative electron microscope radioautography revealed that, at 10 min after 3H-fucose injection, over 70% of the label was localized to the Golgi apparatus, indicating that fucose residues are added to newly synthesized glycoproteins principally at this site. With time the proportion of label associated with the Golgi apparatus decreased, but that assigned to the infolded basal plasma membrane, the apical microvilli, and various apical lysosomes increased. These results indicate that in retinal pigment epithelial cells newly synthesized glycoproteins continuously migrate from the Golgi apparatus to lysosomes and to various regions of the plasma membrane. In this case, the membrane glycoproteins may play specific roles in receptor functions of the basal plasma membrane or phagocytic activities at the apical surface. Very little label migrated to Bruch's membrane, indicating either a very slow turnover or a paucity of fucose-containing glycoproteins at this site.

Distribution of lectin binding sites in rabbit oviduct

The carbohydrate histochemistry of the rabbit oviduct has been examined by the use of four lectins conjugated with horseradish peroxidase as histochemical reagents. Each lectin gave a very distinct typical pattern of binding, but for each lectin there was no difference between the distribution of binding sites in ampulla and isthmus. Wheat germ lectin bound exclusively with the connective tissue of the oviduct folds; winged pea lectin was detected only in the ciliated cells; peanut lectin binding sites were visualized in the secretory cells; the binding reactivity of soybean lectin was limited to the basal part of the cilia. Although it is very difficult at present to correlate the distribution of lectin binding sites with the function of the positive cells, some hypotheses have been advanced.

Mechanisms of glycosylation and sulfation in the Golgi apparatus: evidence for nucleotide sugar/nucleoside monophosphate and nucleotide sulfate/nucleoside monophosphate antiports in the Golgi apparatus membrane

The mechanism of translocation in vitro of sugar nucleotides and adenosine 3'-phosphate 5'-phosphosulfate (PAPS) into the lumen of rat liver Golgi apparatus vesicles has been studied. It has been previously shown that the Golgi apparatus membrane has specific carrier proteins for PAPS and sugar nucleotides. We now report that translocation of the above nucleotide derivatives across Golgi membranes occurs via a coupled equimolar exchange with the corresponding nucleoside monophosphates. An initial incubation of Golgi vesicles with GDP-fucose radiolabeled in the guanidine ring resulted in accumulation within the lumen of radiolabeled GMP. Exit of GMP from these vesicles was specifically dependent on the entry of (additional) GDP-fucose into the vesicles (GDP-mannose and other sugar nucleotides had no effect). GDP-fucose-stimulated exit of GMP was temperature dependent, was blocked by inhibitors of GDP-fucose transport, such as 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and appeared to be equimolar with GDP-fucose entry. Preliminary evidence for specific, equimolar exchange of CMP-N-acetylneuraminic acid with CMP, PAPS with 3'-AMP, and UDP-galactose and UDP-N-acetylglucosamine with UMP was also obtained. These results strongly suggest the existence of different antiport proteins within the Golgi membrane that mediate the 1:1 exchange of sugar nucleotides or PAPS with the corresponding nucleoside monophosphate. Such proteins may have a regulatory role in glycosylation and sulfation reactions within the Golgi apparatus.

Influence of colchicine and vinblastine on the intracellular migration of secretory and membrane glycoproteins: II. Inhibition of secretion of thyroglobulin in rat thyroid follicular cells as visualized by radioautography after 3H-fucose injection

Young (40 gm) rats were given a single intravenous injection of colchicine (4.0 mg) or vinblastine (2.0 mg). At 10 min after colchicine and 30 min after vinblastine administration, the rats were injected with 3H-fucose. Control rats received 3H-fucose only. All rats were sacrificed 90 min after 3H-fucose injection and their tissues processed for radioautography. In thyroid follicular cells of control animals, at this time interval, 57% of the total label was associated with colloid and secretory vesicles in the apical cytoplasm while 27% was localized in the Golgi apparatus and neighboring vesicles. In experimental animals, the proportion of label in colloid and apical vesicles was reduced by more than 69% after colchicine and more than 83% after vinblastine treatment. The proportion of label in the Golgi region, on the other hand, increased by more than 125% after colchicine and more than 179% after vinblastine treatment. Within the Golgi region, the great majority of the label was associated with secretory vesicles which accumulated adjacent to the trans face of the Golgi stacks. It is concluded that the drugs do not interfere with passage of newly synthesized thyroglobulin from the Golgi saccules to nearby secretory vesicles, but do inhibit intracellular migration of these vesicles to the cell apex. In most cells the number of vesicles in the apical cytoplasm diminished, but this was not always the case, suggesting that exocytosis may also be partially inhibited. The loss of microtubules in drug-treated cells suggests that the microtubules may be necessary for intracellular transport of thyroglobulin.

Radioautographic characterization of successive compartments along the rough endoplasmic reticulum-Golgi pathway of collagen precursors in foot pad fibroblasts of [3H]proline-injected rats

Young rats given an intravenous injection of [3H]proline were killed at successive times from 4 to 80 min later. Fibroblasts from the front foot pad were radioautographed ; silver grains were counted over several of the organelles and the results were expressed as percent radiolabel per unit volume. These percentages reached a peak over rough endoplasmic reticulum cisternae at 4 min, intermediate vesicles and tubules at 10 min, spherical distensions of cis-side Golgi saccules at 20 min, cylindrical distensions of trans-side saccules between 40 and 60 min, and secretory granules at 60 min. It is proposed that the succession of peaks corresponds to the migration pathway of collagen precursor proteins within fibroblasts; that is, the proteins synthesized in rough endoplasmic reticulum are delivered by intermediate vesicles and/or tubules to the spherical distensions of cis-side saccules, somehow pass from there to the cylindrical distensions of trans-side saccules and, finally, are carried by secretory granules to the extracellular space.

Immunocytochemical studies on differentiation of the thyroid gland in rabbit fetuses and chick embryos

The morphogenesis of the thyroid gland in rabbit fetuses and chick embryos was investigated using the PAS stain and an immunoperoxidase method with anti-19S-thyroglobulin antiserum. In rabbit fetuses, the reaction for precursor components was firstly detected in the apical portions of follicular cells, arranged in clusters but not yet forming follicles, at 16 days of gestation. Although the first primordial follicles storing colloid droplets were observed on day 18, a drastic increase of follicle formation, the true onset of thyroid function, did not occur until day 22. The colloid in primordial follicles revealed very strong immunoreactivity for 19S-thyroglobulin. The follicles gradually increased in size with age. At 25 days of gestation the cytoplasm of follicular cells was stained densely by slightly diluted 19S-thyroglobulin antiserum, whereas the colloid was stained with highly diluted antiserum; these immunoreactions of follicular cells and colloid were comparable to those of postnatal animals. In chick embryos, significant numbers of primordial follicles were observed throughout the whole thyroid parenchyma at 9 days of incubation. On day 12, the follicles stored more PAS-positive and immunoreactive colloid. At 14 days of incubation follicles with enlarged follicular lumina, having an immunoreactivity similar to mature follicles, became increasingly common.

Two anatomical pathways for the renewal of surface glycoproteins in chloride cells of fish gills

The cytoplasm of chloride cells found in the epithelium lining the gills of guppies (Lebistes reticulatus) contains, in addition to the Golgi apparatus and cisternae of endoplasmic reticulum, two distinct membranous components, the vesiculotubular and the tubular systems. While the latter is connected to the laterobasal plasma membrane, the former, made up of small vesicles and short membranous tubules, is seen mainly between the Golgi apparatus and the apical cavity which invaginates the apex of the cell. The role of these two systems in the transport of glycoproteins from the Golgi apparatus to the cell surface was investigated in fishes maintained in fresh and salt water, injected with 3H-fucose, and sacrificed at various intervals thereafter (10 and 30 min; 2.5, 8, 15.5, 24, and 48 hours). The distribution of the label was analyzed by quantitative radioautography in sections examined with the light and electron microscopes. The light microscopic data suggested that the label incorporated in the supranuclear region, where the Golgi apparatus is located, migrated toward the apical and the laterobasal regions of the chloride cells. The relative concentration of the tracer over the various components of the cytoplasm of these cells was calculated from data collected on electron microscope radioautographs at various intervals after 3H-fucose injection. The curves obtained supported the view that glycoproteins synthesized in the Golgi apparatus were transported to the apical surface via the vesiculotubular system, and to the laterobasal membrane via the tubular system.

Cytological changes induced by low temperature in the thyroid glands of larvae of the salamander Hynobius retardatus

In order to study the environmental conditions and the endocrine mechanism which induce neotenous characteristics, the fine structure of the thyroid glands of larvae of the salamander Hynobius retardatus were examined. The thyroid glands of larvae exposed to a low temperature (4 degrees) were compared with those of larvae exposed to a higher temperature (20 degrees). At 4 degrees, the follicular lumen was large and its contents of low electron density; the epithelial cells were flat or cuboidal. In contrast, the 20 degrees larvae showed a small dense lumen and tall cylindrical epithelial cells, which may indicate a higher level of activity. No apical vesicles were found in the epithelial cells of the 4 degrees larvae, although they were present in 20 degrees larvae. On the other hand, in 4 degrees larvae the chromatin in the nuclei was scattered, while in 20 degrees larvae it was condensed. In addition, large dense granules occupied 2.4% of the epithelial cytoplasm in 4 degrees larvae and as much as 7.3% in 20 degrees larvae. The structural features observed in larvae exposed to the cold resembled those reported for thyroid glands made inactive by a lack of thyrotropin.

Effect of tunicamycin on thyroglobulin secretion

Secretion of thyroglobulin was studied by incubating pig thyroid follicles, isolated by collagenase digestion and opened up by trypsinization. When followed over periods of 4 h, the secretion of [14C]leucine-labeled thyroglobulin into the medium was reduced by 60-95% in the presence of 1 microgram/ml and 5 micrograms/ml of tunicamycin. These concentrations of the antibiotic reduced incorporation of [3H]mannose into the follicle proteins by 70-80% but did not significantly influence the incorporation of [14C]leucine. Rat thyroid lobes were labeled with [3H]leucine for 20 min and chase-incubated for 0-4 h. In electron microscopic autoradiographs obtained immediately after labeling, the label was restricted to the follicle cells and concentrated over the endoplasmic reticulum both in controls and in specimens exposed to tunicamycin (5 micrograms/ml). After 4 h chase most radioactivity was located in the follicle lumen in controls whereas in tunicamycin-exposed lobes almost all labeled material was retained in the follicle cells. It is concluded that tunicamycin suppresses thyroglobulin secretion and that this is not due to inhibited protein synthesis.

Autoradiographic studies of protein and polysaccharide synthesis during vitellogenesis in Drosophila

Quantitative light- and electron-microscopic autoradiography was used to evaluate metabolic processes that occur during late developmental stages (10-14) of oogenesis in Drosophila melanogaster. Major differences in radiolabelling patterns were found after in vivo (10-45 min) uptake of [3H]-monosaccharides and [3H]-L-lysine. Several different methods of data analysis were required to facilitate interpretation of these patterns. [3H]-L-lysine produced extensive cytoplasmic labelling at all developmental stages. In addition, about 15% of alpha yolk spheres were intensely labelled at stage 10, reflecting the incorporation of radiolabelled vitellogenins synthesized during the incubation period. Subsequent stages showed low silver grain density over alpha yolk spheres until stage 14, when a burst of [3H]-L-lysine incorporation by most alpha spheres was observed, possibly indicative of a maturation process for embryogenesis. [3H]-D-glucose and [3H]-D-galactose (10 min, in vivo) both induced intense labelling of the beta yolk spheres in a manner suggesting in situ assembly beginning at early stage 13. Inasmuch as the polysaccharide of beta yolk spheres has the properties of glycogen (e.g., rosette structure digested by alpha-amylase) and the radiolabelled monosaccharides were introduced intra-abdominally, it is evident that transport systems as well as enzymes utilizing glucose and galactose for glycogenesis must be readily available. It is notable that wide-spread labelling of egg chambers was elicited by [3H]-D-glucose and [3H]-D-galactose (e.g., nurse cells, follicle cells, chorion, vitelline membrane), but the labelling induced by [3H]-N-acetylmannosamine was restricted mainly to the endochorion. A possible role of microtubules in distribution and assembly of yolk spheres was inferred when colchicine, admixed to the culture medium (2-5 ppm), produced abnormal distribution and diminution in number of both alpha and beta yolk spheres. In addition to revealing previously unknown metabolic events of vitellogenesis, the results provide additional criteria for stage characterization as well as a means to specifically label certain macromolecules for purposes of isolation.

The biosynthetic pathway of the asparagine-linked oligosaccharides of glycoproteins

This review deals with the structure and addition of the different types of oligosaccharides to asparagine residues in proteins. This process occurs in several steps, first an oligosaccharide which contains N-acetylglucosamine mannose and glucose is built up joined to dolichyl diphosphate. The oligosaccharide is then transferred to a polypeptide chain, loses its glucose, and is modified by removal of some monosaccharides and addition of others giving rise to a variety of saccharides.

Glycoprotein synthesis and migration in beta cells of the islets of Langerhans as shown by quantitative light- and electron-microscopic radioautography

L-3H-fucose was injected intravenously into rats that were killed from 10 min to 7 days after isotope administration. Semi-thin and thin sections of the islets of Langerhans were processed for light- and electron-microscopic radioautography, respectively, and analyzed quantitatively. L-3H-fucose was incorporated into newly synthesized glycoproteins in the Golgi apparatus of the beta cells and subsequently labeled glycoproteins migrated to secretory granules and plasma membrane. Therefore, some of the glycoproteins synthesized by the beta cells of the islets of Langerhans are destined for the renewal of plasma membrane. Although the labeling of the secretory granules was clearly demonstrated, it was not possible to decide if the newly formed glycoproteins are incorporated into the content or into the membrane of the granule. Thus, the fate as well as the function of secretory-granule glycoproteins could not be determined precisely. Several hypothesis concerning the presence of glycoproteins in the secretory granules in relation with insulin metabolism are considered.

The site of incorporation of sialic acid residues into glycoproteins and the subsequent fates of these molecules in various rat and mouse cell types as shown by radioautography after injection of [3H]N-acetylmannosamine. I. Observations in hepatocytes

To study the site of incorporation of sialic acid residues into glycoproteins in hepatocytes, we gave 40-g rats and 15-g Swiss albino mice a single intravenous injection of [3H]N-acetylmannosamine (8 mCi) and then sacrificed them after 2 and 10 min. To trace the subsequent migration of the labeled glycoproteins, we injected 40-g rats with 4 mCi of [3H]N-acetylmannosamine and sacrificed them after 20 and 30 min, 1, 4, and 24 h, and 3 and 9 d. Concurrent biochemical experiments were carried out to test the specificity of injected [3H]N-acetylmannosamine as a precursor for sialic acid residues of glycoproteins. In radioautographs from rats and mice sacrificed 10 min after injection, grain counts showed that over 69% of the silver grains occurred over the Golgi region. The majority of these grains were localized over the trans face of the Golgi stack, as well as over associated secretory vesicles and possibly GERL. In rats, the proportion of grains over the Golgi region decreased with time to 37% at 1 h, 11% at 4 h, and 6% at 24 h. Meanwhile, the proportion of grains over the plasma membrane increased from 4% at 10 min to 29% at 1 h and over 55% at 4 and 24 h; two-thirds of these grains lay over the sinusoidal membrane, and the remainder were equally divided over the lateral and bile canalicular membranes. Many silver grains also appeared over lysosomes at the 4- and 24-h time intervals, accounting for 15-17% of the total. At 3 and 9 d after injection, light microscope radioautographs revealed a grain distribution similar to that seen at 24 h, with a progressive decrease in the intensity of labeling such that by 9 d only a very light reaction remained. Because our biochemical findings indicated that [3H]N-acetylmannosamine is a fairly specific precursor for the sialic acid residues of glycoproteins (and perhaps glycolipids), the interpretation of these results is that sialic acid is incorporated into these molecules in the Golgi apparatus and that the latter then migrate to secretion products, to the plasma membrane, and to lysosomes in a process of continuous renewal. It is possible that some of the label seen in lysosomes at later time intervals may have been derived from the plasma membrane or from material arising outside the cells.

Inhibitory effects of tunicamycin and 2-deoxyglucose on thyroglobulin synthesis

The kinetic incorporation of labelled sugars and amino acids by rat thyroid hemilobes was measured in the presence of 2-deoxyglucose and tunicamycin, inhibitors of the glycosylation of glycoproteins. With either inhibitor the carbohydrate content of exocytosed thyroglobulin was only slightly decreased (less than 20% of control) whereas the rate of exocytosis was strongly inhibited (by 60-80%). As no intracellular accumulation or proteolysis of non-glycosylated molecules was detected, the reduced rate of thyroglobulin release seems essentially due to a decrease in protein synthesis. In a whole cell system (hemilobes), it is impossible to uncouple glycosylation and protein synthesis by incubation with tunicamycin; 50 micrograms/ml tunicamycin for 270 min inhibited total [3H]-glucosamine and 14C-labelled amino acid incorporation by 65% and 33% respectively. This can be contrasted with cell-free incubation of thyroid rough microsomes where glycosylation was blocked by the same tunicamycin concentration (90% inhibition of N-[3H]acetylglucosamine transfer from UDP-N-[3H]acetylglucosamine) whilst ongoing protein synthesis was not significantly modified (less than 4% inhibition). This clearly suggests that, in thyroid follicular cells, a regulatory link exists between the synthesis of the peptide moiety of a glycoprotein and its glycosylation.

Synthesis of secretory and plasma membrane glycoproteins by striated duct cells of rat salivary glands as visualized by radioautography after 3H-fucose injection

The ability of the striated ducts of rat salivary glands to incorporate 3H-fucose into glycoprotein was studied by light and electron microscope radioautography. At 3.5 to 20 minutes after intravenous injection, the majority of the radioautographic grains in the ducts of the parotid gland were localized to the Golgi apparatus. By 40 minutes, the percentage of grains over the Golgi apparatus had decreased; a corresponding increase in grains occurred over small (0.1-0.4 micrometer) apical granules and the highly infolded basal and lateral plasma membranes. By two hours, less than 10% of the label was associated with the Golgi apparatus, while 26% and 28% were attributed to the apical granules and plasma membrane, respectively. By 8 to 12 hours after injection, the number of grains over the apical cytoplasm had decreased, suggesint luminal discharge of the apical granules. In contrast, the basal and lateral plasma membranes remained labeled up to 30 hours after injection as judged by the distribution of grains in light microscope radioautographs. Mitochondria appeared capable of independent incorporation of fucose, accounting for about 20% of the grains from ten minutes to two hours after injection. Comparable results were obtained in the striated ducts of the submandibular and sublingual glands. These results indicate that the striated duct cells readily incorporate 3H-fucose into newly-synthesized glycoproteins. A portion of these are secretory glycoproteins which are packaged and stored in the apical granules, and a portion are membrane glycoproteins which are incorporated into the extensive plasma membrane of these cells.

C cell (parafollicular cell) -- immunoreactive thyroglobulin: purification, identification and immunological characterization

In relation to our earlier finding that the thyroglobulin-like material responsible for the cytochemical immunoreaction of C cells was obtained in the peak I fraction of Bio-Gel A-5 m, which included faster sedimenting components of thyroglobulin, the present study has identified the positive reacting component and clarified its immunochemical and immunohistochemical properties. 1. The peak I fraction of dog and hog thyroglobulin was chromatographed on a Bio-Gel A-50 m column. Antiserum to the faster eluted peak I'1 only immunoreacted with C cells. The peak I'1 was then refiltered on Bio-Gel A-150 m column. Antiserum to peak I''1 fraction of both species which was eluted in the first part had high immune specificity for C cells. 2. When 4-30% and 2-16% continuous gradient gels of polyacrylamide were employed, peak I''1 represented a single electrophoretic band corresponding to the component with the largest molecular weight in thyroglobulin. The protein was named C-thyroglobulin. The molecular weight was approximately 2,600,000, four times as large as 19 S, as calculated by relative mobility on the 2-16% gradient gel. 3. In double diffusion tests, anti-peak I''1 antiserum produced two immunoprecipitin lines with its own antigen. The reaction was different from that of anti-19 S antiserum which formed a single line. 4. On immunoperoxidase staining, anti-peak I''1 antiserum reacted to C cells in exactly the same way as anti-calcitonin antiserum. 5. When anti-peak I''1 antiserum was absorbed with calcitonin, the subsequent reaction of the C cells was greatly decreased. The absorption of anti-calcitonin antiserum with increased amounts of peak I''1 abolished the C cell reaction. On the basis of these observations, the possibility that C-thyroglobulin is a biosynthetic precursor of calcitonin exists.

Metabolic-morphologic events in the integument of the Pacific hagfish (Eptatretus stoutii)

Light- and electron-microscopic autoradiography were used to obtain a coordinated metabolic-morphologic view of some of the events of cellular differentiation that occur across the epidermis of the Pacific hagfish (Eptatretus stoutii) and which enable this animal to secrete copious amounts of mucus. As judged by epidermal incorporation of [3H]-thymidine in vivo, about 98% of DNA replication is confined to the basal three layers of the total of 6--8 layers of cells. Small mucous cells (SMC), the most numerous of the three major cell types involved in mucigenesis, show in vitro and in vivo radioincorporation profiles of [3H]-L-lysine and [3H]-D-glucosamine which differ markedly from those of [3H]-L-fucose and [3H]-D-galactose. Time-course incorporation profiles (mean silver grains/cell and percentage of cells with at least one cluster of silver grains) of [3H]-L-lysine and [3H]-D-glucosamine not only reflected the metabolic activities of cell renewal and differentiation in basally-located cells but also the high mucigenic activity in cells near the epidermal surface. By contrast, [3H]-L-fucose and [3H]-D-galactose were mainly incorporated by the more mature SMC in juxtanuclear regions near Golgi complexes and newly formed secretory vesicles. The intensity of [3H]-fucose labeling appeared proportional to the intensity of histochemical staining of the apical cytoplasm. The prominent capsule, within SMC in basal and lateral regions, which arises from a tight intermingling of tonofilaments, appears to restrict secretory vesicles to apical regions while the cell progressively differentiates and migrates to the epidermal surface. The other mucigenic cell types, large mucous cells and thread cells, each show distinctive differentiation and radioincorporation patterns.

Cytochemical localization of complex carbohydrates in the thyroid gland of normal and TSH-treated mice

The silver methenamine method for the ultrastructural localization of carbohydrates and glycoproteins was applied to the thyroid glands of normal and TSH-treated mice. The majority of the cisternae of the rough endoplasmic reticulum showed a weak, but apparently positive reaction. These findings support the opinion that glycosylation of thyroglobulin occurs initially in the rough endoplasmic reticulum. By this method the Golgi apparatus was observed to display a staining gradient. The intermediate to inner saccules were intensely stained, whereas the outer saccules were not so heavily stained. This phenomenon indicates that the Golgi apparatus has a functional polarity for the addition of carbohydrates to thyroglobulin and other proteins. In the inner and/or the peripheral regions of the Golgi apparatus and in the apical cytoplasm, a large number of globules of various sizes, considered to be colloid droplets, lysosomes and apical secreting vesicles, showed a positive reaction. The luminal colloid was also positive with silver methenamine staining, with almost the same intensity as the globules and vesicles.

High resolution radioautographic study of newly formed protein in striated muscle with emphasis on red and white fibres

The elaboration and distribution of newly formed proteins in the striated muscle of 21-day-old mice were investigated by quantitative radioautography at intervals between 2 and 240 min after intravenous injection of tritiated leucine. In radioautographs, the localization and the relative label concentration were comparatively estimated for the different components of mitochondria-rich fibres, in particular of red fibres, from the tibialis anterior muscle and of mitochondria-poor fibres from the oesophageal muscle. As early as 2 min after injection, radioactivity was detected over the nucleus, the polysome-rich sarcoplasm, the A and I bands, the Z lines, and the mitochondria in the two fibre types. Label localization did not change with time. The relative label concentration increased similarly in the polysome-rich sarcoplasm and the A and I bands of both fibre types within 30 min after injection, a confirmation that biosynthesis of myofibrillar proteins takes place rapidly. In each case, concentration was higher in the Z lines than in the I bands, and higher in the I bands than in the A bands, thus showing "in vivo" that the rates of synthesis of sarcomere protein components are not uniform. However, the relative label concentration was found to be higher in the Z lines of mitochondria-poor fibres than of mitochondria-rich fibres: this suggests that a higher synthetic rate of Z line protein, and probably of alpha actinin, is characteristic of the first type. Inversely, the concentration was higher in the mitochondria of mitochondria-rich fibres. This lead to the belief that high rate of protein synthesis in these organelles may account for the high rate of label incorporation into this type of fibre.

Synthesis and migration of glycoproteins in cells of the rat thymus, as shown by radioautography after 3H-fucose injection

Young male rats received a single intravenous injection of 3H-fucose and were killed after various time-intervals. Light- and electron-microscopic radioautographic studies of the thymus in animals killed shortly after injection showed that all of the different cell types present incorporated 3H-fucose label. The heaviest uptake occurred in macrophages and in hypertrophic epithelial cells located near the cortico-medullary border. Somewhat lighter incorporation was observed in medullary and cortical stellate epithelial cells and in cells designated as special cells, while the lightest reaction appeared over lymphocytes. In all cells the label was localized initially to the Golgi apparatus, where, presumably, it was incorporated into glycoproteins. With time, some of the labeled putative glycoproteins in all cell types migrated to the plasma membrane. In macrophages, much of the label migrated to lysosomal bodies, while in the special cells the label migrated to dense bodies which may also be of lysosomal nature. In stellate and hypertrophic epithelial cells much of the label migrated to characteristic vacuoles. The possible relationship between the observed glycoprotein synthesis in these cells and hormone production is discussed.