High-resolution scanning-densitometry of photographic negatives of human chromosomes

Summary Principles and techniques are discussed for measuring with high topological resolution local emission in fluorescing objects, using photographic negatives.Determination of fluorescence intensities is only possible when an unequivocal relation between the original local fluorescence emission intensities of the object, and the transmittances or densities recorded in the microfluorophotograph is known. This relation is formulated in the theoretical part.From this relation it can be concluded that the recorded intensities can be measured optimally when the optical density values produced by the fluorescence emission fall in the range of the linear portion of the Hurter and Driffield curve. In order to obtain this situation, a uniform, low-level preexposure of the film emulsion to (white) light is carried out prior to the actual fluorescence emission exposure. This pre-exposure acts to elevate the signal exposure to the linear (steeper) part of the H.-D. curve.Inhomogeneity of the excitation beam in the object field, or differences in film emulsion response to the light exposure, will result in erroneous optical densities recorded in the photographic negative. Correction for such artifacts could be obtained by addition of a low concentration of fluorophore to the mounting medium of the microscopic preparation. The overall fluorescent background produced in this way, enabled calibration of local fluorescence intensities in different parts of one fluorophotographic negative, and also of the intensities in different negatives taken from one microscopic preparation.The validity of this approach was checked by comparing data obtained from several photographic negatives of the same quinacrine-stained metaphase, taken with different exposure times to imitate fluctuations in excitation illumination, after conversion of the scanning data into emission intensity values with an algorithm based on the proposed theoretical relation.In another experiment, fluorescence emission intensities of Feulgenstained chromosomes which had been measured with a cytofluorometer, were compared with results obtained by conversion of the scanning data measured in the fluorophotographic negatives of the same metaphases. Both types of experiment confirmed the applicability of the procedure described.Supported by grant nr 28-169 of the Praeventiefonds, The Hague     

Some aspects of the fine structure of the reticulo-endothelial system; the cells which clear colloids from the blood stream

Summary The macrophages in various sites in the mouse have been examined with the electron microscope in normal animals, and in animals which had recently received intravenous colloids. There was a general structural similarity at all sites. The most obvious common feature was the presence of small granules which stain with toluidine blue. These were of two types. One, the smaller had a finely granular substructure and may represent the primary lysosome; the other, the larger was heterogeneous, contains banded probably fibrillar material with a repeating pattern of 35–50 A, and may represent the residual body.Colloids given intravenously were cleared by phagocytosis by endothelial cells and endothelial macrophages, by leakage through patent intercellular junctions, and by phagocytosis by paravascular macrophages. Such clearance is commonly held to be a measure of reticulo-endothelial function. This measure is therefore clearly dependent on several cellular factors.I am grateful to Prof. R. Barer for his advice and criticism, to Dr. G.A. Meek for guidance on electron microscopy, and to Mrs. B. Romans and Miss M. Tune for technical and photographic assistance.This work was supported by grants from the M.R.C. and the University of Sheffield Tuberculosis Research Fund and by a grant to the Department from Unilever Ltd.     

Observations on neurons and neuroglia from the area of the mesencephalic fifth nucleus of the cat in vitro

Summary Neurons from the mesencephalic root of the fifth nucleus from the kitten have been maintained in vitro for periods up to 70 days. During this time they retained their characteristic form and structure as seen in sectioned material. Axonic processes as long as 8 mm have been measured. The occurrence of recurrent axons intertwining with dendritic arborizations of the same neuron is discussed. Modulations are described for astrocytes in relation to their possible dependence on the scarcity of connective tissue elements and a lack of an outer mesenchymal tissue zone in cultures of mesencephalic explants.Grateful acknowledgment is made to Mrs. Walther Hild and Mrs. C. C. Morris for their generous contribution in the management of the tissue cultures and in executing staining procedures. Messrs G. Lefeber and E. Pitsinger offered indispensable aid with photographic work.This investigation was supported by a grant [PHS B-364 (C3)] from the National Institute of Neurological Diseases and Blindness, of the National Institutes of Health, Public Health Service, administered by C. M. Pomerat.     

Scanning electron microscopic studies of cilia

Summary A simple method for the preparation of ciliated epithelia for study with the scanning electron microscope is described. Ciliary groups are well preserved and it is possible to discern individual cilia and work out their numbers and orientation. Following scanning electron microscopical study some of the material was prepared for transmission electron microscopy and the ultrastructure of the tissue was found to be surprisingly well preserved. The tracheal epithelium of the rabbit, the olfactory epithelia of the goldfish and the rabbit, and the sensory epithelia in the statocyst of a cephalopod mollusc were examined with the scanning electron microscope to demonstrate the possibilities of the method. Acknowledgements. We would like to thank Professor J. Z. Young for his continued interest and support. The scanning electron microscope was purchased with a grant provided by the Science Research Council to Dr. Boyde, Mr. R. Willis helped in the initial stages of the study, Mr. G. Savage provided help with the goldfish material, Mr. S. Waterman provided much photographic assistance, and Mrs. N. Finney the secretarial assistance.     

Nerve supply and distribution of cholinesterase activity in the external nose of the mole

Summary Nerve supply and the distribution of cholinesterase activity were studied in the skin of the external nose of seven moles using a simplified Bielschowsky-Gross silver method and Koelle's histochemical technique.The sensory units of the mole's nose or the organs of Eimer are surrounded by blood sinuses which facilitate their movements during mechanical stimulation. All nerve fibres of the plexus deep to the basal cell layer of Eimer's organ ultimately become intra-epidermal endings. Contrary to the findings of earlier investigators, Merkel's discs, Pacinian corpuscles and Ruffini corpuscles have not been observed at the base of Eimer's organ. In the superficial layer of the plexus, the Schwann sheath cells increase in number, undergo modification and give a positive cholinesterase reaction.It is suggested that the organ of Eimer, the specialised nerve plexus deep to it and the surrounding blood sinus together constitute the touch receptor on a similar principle of transmission by leverage as in the tactile hair or the intermediate ridge of the papillary ridge.The role of the intra-epidermal nerve endings of the mole's nose as tactile receptors is disputed. A suggestion is made that tnese nerves may constitute pain and temperature receptors and that several modalities of sensation may be carried to the brain along one and the same medullated axon.We gratefully acknowledge the technical assistance of Miss Jill Hocknell. Our thanks are also due to Mr. C. J. Duncan and the staff of the Photography Department for their aid with the photographic work. We are particularly grateful to Mr. D. Burgess of the Ministry of Agriculture and Fisheries for kindly supplying us with live moles. One of the authors (N.C.) acknowledges an equipment grant from the Royal Society.     

Sudanophilia and lipids in the blood and marrow cells

Summary The method of Sheehan and Storey, used for demonstrating stable Sudanophilia of neutrophils in smears, was modified by substituting other alcohols (from methanol to amyl alcohol) for ethanol, and the effect of this on the resulting staining reactions was investigated. The intensity of the staining of the neutrophil granules decreases with increasing number of carbon atoms in the alcohol, with a gradation of staining from black to yellow, while, at the same time the staining of the erythrocytes increases. The best solvent for Sudan black B for haematological purposes is methanol. This solvent was further used for investigations on various procedures for detecting so-called masked sudanophilia. The most constant and interesting results were obtained after the action of mercuric ions on smears fixed in formalin vapour. Under certain conditions, a characteristic binding of different fractions of Sudan black B on different blood cells can be attained, so that neutrophil granules are stained brown, monocytes mostly grey, lymphocytes, platelets, megakaryocytes, plasmocytes and perinuclear areas of normoblasts blue. The present experiments with various substrates indicate that demasked blue staining in the cytoplasm may be conditioned by phospholipids, although a reaction with other components of the cytoplasm cannot be excluded. The method described may be useful in haematology for studying cytogenetic relations in the monocytic and granulocytic series.Technical Assistance: V. LodrovÁ.     

Nuclear membranous whorls

Summary Membranous whorls have been seen in the nuclei of peritoneal and testicular cells which had been subjected to various experimental manoeuvres. It seems likely that this is an early manifestation of cell degeneration which is demonstrated readily only by glutaraldehyde fixation, and to that extent can be regarded as a glutaraldehyde artifact. Acknowledgements. This work was supported by grants from the Medical Research Council, and the University of Sheffield Tuberculosis Research Fund, and by a grant to the Department from Unilever Ltd.I am grateful to Professor R. Barer for his advice and criticism, to Dr. G. A. Meek for guidance on electron microscopy, to Dr. E. J. Clegg for permission to use material from joint experiments. Technical and photographic assistance was provided by Messrs. P. GarLick and L. Murgatroyd and by Miss M. Tune.     

Activity manifestations of Hassall's corpuscles in vitro as revealed by cinematography

Summary Thymic explants from newborn rats were cultivated in Rose chambers under dialysis membranes. With the use of phase contrast, time-lapse cinematography, the following activity manifestations were observed: 1. Several corpuscles showed rotatory movements; 2. nuclear rotation was observed in some cells of the corpuscles; 3. some individual cells in the 15-day culture showed pulsatile activity which might be involved in the mechanism of the rotatory movements of the cellular aggregates; 4. the corpuscles increased in size by the addition of cells and/or by mitosis; 5. the elements at the periphery of the more mature corpuscles (7- and 9-day cultures) were viable, while the central area appeared to be composed of necrotic tissue or hyalinized material.Grateful acknowledgement is made to Dr. C. M. Pomerat for encouragement in the course of this study. Mr. Charles Raiborn aided in the preparation of cultures and Messrs. C. G. Lefeber and Robert Olson rendered indispensable assistance with the photographic work.Aided by an American Cancer Society Student Fellowship (USC-IDC) and in part by Grant No. G-14091 from the National Science Foundation administered by C. M. Pomerat.     

Electron microscopic observations of synaptic endings in cultures of mammalian central nervous tissue

Summary Synapses were found in rat cerebellar and brainstem cultures with the electron microscope. Three distinct types of synaptic terminals were described. The similarity between synapses found in vitro and in vivo was emphasized.Supported by USPHS Grants 5 Tl 459-04 and NB 03114-03S1 from the National Institutes of Health, Bethesda, Maryland.The authors wish to express their sincere appreciation to Mrs. Eleanor Morris for her assistance in preparing the cultures and Mr. Earl Pitsinger for his photographic assistance.     

Cilia and other surface structures of the trochophore of Harmothoë imbricata (Polychaeta)

Summary Ciliary aggregations occur as the prototroch, neurotroch, apical system and as tufts associated with the eyes and superficial glands. The major collection of cilia is the locomotory organ or prototroch that runs around the equatorial plane of the larva. This band is composed of four contiguous rows of cells, the two medial rows bearing the long locomotory cilia. The cilia occur in clumps, with several clumps arising from each prototroch cell while both the main cells contribute to each clump. The central filaments of these cilia are orientated at right angles to the long axis of the clump, the direction of ciliary beat being at right angles to the progression of the metachronal wave along the prototroch. The neurotroch, extending from the mouth to the posterior pole of the larva, beats away from the mouth. The rate of beating is rapid, and the cilia are short. The apical area of the larva is bordered by five single lines of compound cilia that surround a few stiff cilia. All the cilia beat occasionally. A further line of cilia, the akrotroch, exists at a position halfway between the apical area and the prototroch on the same side as the mouth. These cilia beat towards the prototroch. Some of these cilia are associated with sets of glandular openings. The fine structure of the glands and cuticle is described. The glands are small mucous glands that open via a projecting pore which is encircled by rings of microvilli. They often occur in groups of four or in pairs. The cuticle is similar to that described previously for adult polychaetes.This work was started under a Science Research Council (U.K.) grant (B/SR/1871) for a Research Assistantship to Dr. M. S. Laverack and grateful acknowledgement is made for this. We would like to thank Dr. A. Boyde for all his advice and use of apparatus. The scanning electron microscope used in this study was provided by a Science Research Council (U. K.) grant to Dr. Boyde. We would like to thank Mrs. J. Parkes for photographic assistance.     

Development of the acrosomic system of the spermatozoon in the Norwegian lemming (Lemmus lemmus)

Summary An electronmicroscopic study on the development of the acrosome system of the spermatozoon in the Norwegian lemming (Lemmus lemmus) has been performed. The proacrosomal granules were found to be few and to consist of a dense center and a less dense periphery, and the acrosomal vesicle to contain stainable material of the same structure but of lower density than that of the acrosomal granule. Like in the guinea pig, two zones of different density exist throughout acrosome development and are visible also in mature spermatozoa. A large osmiophilic formation consisting of saccular, tubular, and lamellar structures, was found between the apex of the condensed nucleus and the acrosome and was identified as perforatorium.We are greatly thankful to Dr. Antti Telkkä, and Mr. Mauri Nyholm, M. Sc. for expert advise in electronmicroscopy and Mr. P. Lehtimäki for photographic help. For the supply of the lemmings we are indebted to Prof. K. Lagerspetz, and Mr. O. Hissa, M. Sc. This work is related to a series of studies on the biology of the Norwegian lemming (for previous works see Asp et al.).     

Die Aufnahme von 14CO2 und die Verteilung des 14C auf freie Aminosäuren und auf Proteinaminosäuren im Hellrot und im Blaulicht. [Objekt: Farnvorkeime von Dryopteris filix-mas (L.) Schott]

Summary Morphogenesis and metabolism of the early gametophytes (= sporelings) of the common male fern are controlled by light. The normal two-dimensional development of the gametophytes in white or blue light is correlated with an increase in protein content; inred light alone, on the other hand, the sporelings remain filamentous, and the protein content is markedly lower (cf. Mohr, 1965). The problem has been whether blue light increases the rate of protein synthesis or decreases the rate of protein degradation. This problem was solved in the present paper by the use of ¹⁴CO₂. Blue light promotes specifically the rate of protein synthesis as indicated by the increase of ¹⁴C incorporation into protein-bound amino acids under blue light as compared with red light.Using ¹⁴CO₂ we have analyzed the kinetics of free amino acid synthesis (Fig. 4) and protein synthesis (Fig. 5) under steady state conditions of photosynthetic CO₂ incorporation in blue or red light (Fig. 3). Under our conditions the rate of photosynthesis is about 1.5 times higher under blue light than under red light (Fig. 3, Table 1).The facts that the total pool sizes of the free amino acids are smaller in blue than in red light (v. Deimling and Mohr, 1967; Table 2) and that, on the other hand, the ¹⁴C-contents of the thoroughly labelled amino acid pools are virtually identical in blue and red (Table 3) indicate (a) that the pool sizes of these labelled amino acids may be equal in both light qualities and (b) that there is a compartmentation of free amino acid pools in the fern sporeling. This problem will be dealt with more in detail in a forthcoming paper on the behaviour of alanine in the fern sporeling (Payer, 1969).Protein synthesis is obviously much stronger under blue light than under red light. The detailed kinetics (Fig. 5b) indicate the involvement of two sorts of proteins: a relatively small part with high turnover which is rapidly labelled with a small but significant difference in red and blue, and a larger part with a slower turnover, the synthesis of which is strongly favored by blue light. — The first sort could be enzyme protein; the latter sort might be structural protein of the chloroplasts. These organelles increase dramaticly in size under the influence of blue light (Bergfeld, 1963). The amino acid composition of the protein, however, does not show any qualitative difference in gametophytes grown in blue or red light (v. Deimling and Mohr, 1967, Table 4).

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Die Aufnahme von ¹⁴CO₂ und die Verteilung des ¹⁴C auf freie Aminosäuren und auf Proteinaminosäuren im Hellrot und im Blaulicht. [Objekt: Farnvorkeime von Dryopteris filix-mas (L.) Schott]

     

Ein spezifischer Einfluß von Blaulicht auf den Einhau von photosynthetisch assimiliertem 14C in das Protein von Farnvorkeimen [Dryopteris filix-mas (L.) Schott]

Summary Morphogenesis and metabolism of the early gametophytes (=sporelings) of the common male fern are controlled by light. The normal two-dimensional development of the gametophytes takes place only in white or blue light; in red light alone, on the other hand, the sporelings remain filamentous even under conditions of equal photosynthetic rate.The problem has been whether blue light exerts its morphogenic influence through differential gene activation. In other words: does blue light mediate the synthesis of morphogenic enzymes which are required for normal morphogenesis. In an earlier paper (Drumm and Mohr, 1967) we have shown that blue light increases the rate of RNA synthesis within an hour whereas the first indication of a morphogenic change due to blue light is only discernible about 3 hours after the onset of blue light (Figs. 1,2). Furthermore we have shown (Mohr, 1965) that Actinomycin D specifically inhibits the blue light mediated morphogenic alterations, and Bergfeld (1967) has shown that blue light will rapidly lead to changes in nuclei and nucleoli in the fern sporelings. In the present paper it has been shown that blue light does increase the rate of protein synthesis about an hour after the transfer of the sporelings from the red into the blue light of equal quantum flux density (350 pE·cm^-2·s^-1).The rate of protein synthesis was measured in shortterm experiments (40min) using ¹⁴CO₂. The photosynthetic rate was the same in red and blue; it was not influenced by the transfer(Fig. 3). Likewise the rate of ¹⁴C incorporation into the pool of free amino acids was not significantly different in red and blue light (Fig.4). On the other hand, the rate of incorporation of ¹⁴C into the protein increased rapidly after the transfer of the sporelings from the red into the blue light (Fig. 5). The same phenomenon (no influence of blue light on the specific activity of the free amino acid; a strong promotive influence on the specific activity of the protein-bound amino acid) was observed in the case of alanine which was investigated in detail (Figs. 6, 7). Since the increase of the protein content of the sporelings is not significant during the first six hours after transfer to blue light (Fig. 8) the protein induced by blue light and directly related to morphogenesis can only be a very small fraction of the total protein of the sporeling.The data strongly support the hypothesis (Ohlenroth and Mohr, 1964), that the morphogenic effect of blue light on the fern sporelings is due to the induction of morphogenic enzymes by blue light.     

The structure of a photoreceptor organelle in the eye of Pterotrachea mutica

Summary The photoreceptor cell of Pterotrachea consists of an elongated cell some 100 m long with recogniseable inner and outer segments. The photoreceptor membranes point towards the light. There are about 300 discs per photoreceptor, a small number of discs arising from a single ciliary base. There are bout 75–100 such bases on each receptor cell. The receptor cells themselves (the inner segments) have four recognisable regions. The vacuolated region, the region of mitochondria, the nuclear region, and the axonal region.The photoreceptor cells are organised in five roughly parallel rows, and separated from one another by pale supporting cells.My thanks are due to Professor J. Z. Young, F. R. S. for his enthusiastic support and help during this work. Dr. R. Bellairs kindly provided electron microscope facilities. Mr. R. Moss, Mrs. J. Hamilton and Mr. A. Aldridge provided excellent technical and photographic assistance.     

Some aspects of the fine structure of the statocysts of the molluscsPecten andPterotrachea

Summary The statocyst ofPecten is composed of hair cells and supporting cells. The hair cells bear kinocilia and microvilli at their distal ends and the supporting cells bear microvilli. The cilia have a 9+2 internal filament content, and arise from basal bodies that have roots, basal feet and microtubular connections. Two different ciliary arrangements are described, one with a small number of cilia arranged in a ring, and another with many more cilia arranged in rows. Below the hair cells are probable synapses. A ciliated duct connects to the lumen of the static sac and passes through the centre of the static nerve. The hair cells in the statocyst ofPterotrachea bear kinocilia and microvilli. The possible importance of cilia and microvilli in the transduction process is discussed.We would like to thank ProfessorJ. Z. Young for bringing specimens ofPterotrachea from Naples and also the staff of the Stazione Zoologica for the provision of specimens, Dr.M. Land for providing specimens ofPecten, the Science Research Council (U.K.) for providing the electron microscope used in much of the study and also for a grant to one of us (V.C.B.), and Mrs.J. Parkers and Mr.R. Moss and Mrs.J. Hamilton for much photographic and technical assistance.     

Glycogen in the neurohypophysis of toads

Summary Studies with the electron microscope revealed the presence of glycogen granules in the neurohypophysis of toads (Bufo arenarum Hensel). The glycogen appeared as scattered particles or as clusters formed by these particles within the nerve fibers. The scattered granules were intermingled with the neurosecretory granules and with the microvesicles. Chemical assays showed the presence of glycogen in the neurointermediate lobe of the toad's hypophysis.This work was supported by research grants from the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and The Rockefeller Foundation.The authors wish to express their appreciation to Prof. Bernardo A. Houssay and to Dr. Luis F. Leloir for their encouragement during the preparation of this paper; to Miss Susana Camocardi for her technical assistance and to Mr. Luis Millara for the photographic work.     

Isolation of a new flavonol glycoside and its effects on the blue color of seed coats ofOphiopogon jaburan

From the blue seed coats ofOphiopogon jaburan, a new flavonol glycoside was isolated as needles and determined to be kaempferol 3-O-β-d-galactoside-4′-O-β-d-glucoside (OK-2) by UV and NMR spectral analyses. OK-2 and kaempfrol 3, 4′-di-O-β-d-glucoside (OK-1), which was detected previously, in the blue seed coat were present in a molar ratio of about 13:7. OK-2 was newly found as a factor causing the blueing effects on ophionin which is a main anthocyanin in the blue seed coats. The mixture of 4.8×10⁻³ M OK-2 and 2.5×10⁻³ M ophionin in Mcllvaine's buffer solution (pH 5.6) showed stable blue color, and the absorption spectrum of the mixture showed two absorption peaks and a shoulder in visible reasion, coinciding with that of the fresh blue seed coat. The effect of ophionin and OK-2 co-pigmentation on the blue color of seed coat ofO. jaburan was discussed.     

Phase contrast photomicrography of cellular behaviour in spongillid porocytes (Porifera: Spongillidae)

The combination of phase contrast photomicrography with a method for phase contrast observation of living sponges facilitated the initial photographic record of spongillid porocyte cellular behavior. Porocytes ofCorvomeyenia carolinensis Harrison (Spongillidae) exhibit true intracellular pores and are components of the incurrent system. The number of porocyte contractile vacuoles increases during pore dilation. This increase is possibly related to an increase in the amount of cell surface in contact with the hypotonic aqueous environment. The porocyte cell type appears closely related to, and is likely derived morphogenetically from, pinacocytes of the upper pinacoderm.     

Some studies on the fluorescence of mast cells after paraformaldehyde treatment

Summary Air dried peritoneal fluid and tissue spreads from rat, mouse, hamster, rabbit, guinea pig, cat, chicken, and frog were treated with paraformaldehyde (pCHO) at 80 ° C for 1 hr. Only rat and mouse mast cells fluoresced. In the rat, mast cells fluoresced whether present in vascular or avascular areas of mesentery, in fat depots, or in peritoneal fluid. Photographs were obtained by fluorescence microscopy, the preparations were then stained and the same fields rephotographed in white light. Comparison of the photographs showed that every fluorescent rat mesentery mast cell also stained with acidified toluidine blue and with Astrablau; a few fluorescent cells did not stain with toluidine blue and an occasional cell that did not fluoresce stained with this dye or with Astrablau. Paraformaldehyde depressed somewhat toluidine blue, inhibited strongly Astrablau, and abolished Alcian blue binding. It had no effect on the staining of purified heparin in model experiments.Reserpine administration in the rat did not prevent visualization of mast cells by the pCHO method.These experiments indicate that all rat mast cells contain serotonin, regardless of cell size (age ?) or site and suggest that no massive, cyclic release of this amine occurs either physiologically or in response to reserpine treatment.Some of the experiments for this paper were carried out in the laboratory of Dr. G. Bloom, Department of Cell Research and Genetics, Karolinska Institutet, Stockholm, Sweden, (September and October, 1963). I wish to acknowledge the help and cooperation of the members of his staff, and especially Dr. Martin Ritzén, whose open, warm, efficient and enthusiastic manner enabled me to accomplish much in a relatively short time. Availability of darkroom facilities to pursue much of the work in the laboratories of Dr. W. Bargmann, Anatomisches Institut, Neue Universität, Kiel, Germany and of Dr. R. Robineaux, Hôpital St. Antoine, Paris, is also gratefully acknowledged. Grant support was furnished by the American Heart Association (62 G 118) and NSF (GB-4166) (to the author), by NIH 5 T 1 GM 102, and by the Swedish Medical Research Council (to Prof. B. Uvnäs and Dr. G. Bloom).This paper is dedicated to Dr. Berta Scharrer on the occasion of her 60th birthday.     

Expression of a sugar-transporter gene family in a photoautotrophic suspension culture of Chenopodium rubrum L.

Photoautotrophic suspension-culture cells of Chenopodium rubrum L. were shifted to mixotrophic growth by adding glucose to investigate whether the activities of plant sugar transporters, as well as the expression of the corresponding genes, are regulated in response to sugars. The rate of d-glucose uptake was shown not to be affected by mixotrophic growth in the presence of d-glucose. The polymerase chain reaction (PCR) technique was applied to amplify cDNA and genomic fragments from monosaccharide-carrier genes. Seven members of a monosaccharide-carrier family were identified of which three were found to be expressed in the suspension-culture cells. The expression of the monosaccharide-carrier genes was independent of the presence of d-glucose.Abbreviation PCR polymerase chain reaction We would like to thank Michaela Bittner, Rainer Ehneß and Monika Kammerer for skillful technical assistance and S. Buchhauser and H. Hallmer for photographic work. This work was supported by the Deutsche Forschungsgemeinschaft (SFB 43) and by Fonds der Chemischen Industrie.