Cerebroside sulfotransferase in Golgi-enriched fractions from rat brain

Glycosphingolipids in congenital disorders of glycosylation (CDG)

Congenital disorders of glycosylation (CDG) are a large family of rare disorders affecting the different glycosylation pathways. Defective glycosylation can affect any organ, with varying symptoms among the different CDG. Even between individuals with the same CDG there is quite variable severity. Associating specific symptoms to deficiencies of certain glycoproteins or glycolipids is thus a challenging task. In this review, we focus on the glycosphingolipid (GSL) synthesis pathway, which is still rather unexplored in the context of CDG, and outline the functions of the main GSLs, including gangliosides, and their role in the central nervous system. We provide an overview of GSL studies that have been performed in CDG and show that abnormal GSL levels are not only observed in CDG directly affecting GSL synthesis, but also in better known CDG, such as PMM2-CDG. We highlight the importance of studying GSLs in CDG in order to better understand the pathophysiology of these disorders.

Who moves the sphinx? An overview of intracellular sphingolipid transport

Lipid bilayers function as boundaries that enclose their content from the surrounding media, and the composition of different membrane types is accurately and dynamically tailored so that they can perform their function. To achieve this balance, lipid biosynthetic machinery and lipid trafficking events are intertwined into an elegant network. In this review, we focus on the intracellular movement of sphingolipids mediated by sphingolipid transfer proteins. Additionally, we will focus on the best characterized and understood mammalian sphingolipid transfer proteins and provide an overview of how they are hypothesized to function. Some are already well understood, while others remain enigmatic. A few are actual lipid transfer proteins, moving lipids from membrane to membrane, while others may have more of a sensor role, possibly reacting to changes in the concentrations of their ligands. Considering the substrates available for cytosolic sphingolipid transfer proteins, one open question that is discussed is whether galactosylceramide is a target. Another question is the exact mechanics by which sphingolipid transfer proteins are targeted to different organelles, such as how four phosphate adapter protein-2, FAPP2 is targeted to the endoplasmic reticulum. The aim of this review is to discuss what is known within the field today and to provide a basic understanding of how these proteins may work.

Mini review: Lipids in Peripheral Nerve Disorders

Neurons are polarized cells whose fundamental functions are to receive, conduct and transmit signals. In bilateral animals, the nervous system is divided into the central (CNS) and peripheral (PNS) nervous system. The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Sensory axons can be up to 3 feet in length. Because of its long-reaching and complex structure, the peripheral nervous system (PNS) is exposed and vulnerable to many genetic, metabolic and environmental predispositions. Lipids and lipid intermediates are essential components of nerves. About 50 % of the brain dry weight consist of lipids, which makes it the second highest lipid rich tissue after adipose tissue. However, the role of lipids in neurological disorders in particular of the peripheral nerves is not well understood. This review aims to provide an overview about the role of lipids in the disorders of the PNS.

Properties, metabolism and roles of sulfogalactosylglycerolipid in male reproduction

Sulfogalactosylglycerolipid (SGG, aka seminolipid) is selectively synthesized in high amounts in mammalian testicular germ cells (TGCs). SGG is an ordered lipid and directly involved in cell adhesion. SGG is indispensable for spermatogenesis, a process that greatly depends on interaction between Sertoli cells and TGCs. Spermatogenesis is disrupted in mice null for Cgt and Cst, encoding two enzymes essential for SGG biosynthesis. Sperm surface SGG also plays roles in fertilization. All of these results indicate the significance of SGG in male reproduction. SGG homeostasis is also important in male fertility. Approximately 50% of TGCs become apoptotic and phagocytosed by Sertoli cells. SGG in apoptotic remnants needs to be degraded by Sertoli lysosomal enzymes to the lipid backbone. Failure in this event leads to a lysosomal storage disorder and sub-functionality of Sertoli cells, including their support for TGC development, and consequently subfertility. Significantly, both biosynthesis and degradation pathways of the galactosylsulfate head group of SGG are the same as those of sulfogalactosylceramide (SGC), a structurally related sulfoglycolipid important for brain functions. If subfertility in males with gene mutations in SGG/SGC metabolism pathways manifests prior to neurological disorder, sperm SGG levels might be used as a reporting/predicting index of the neurological status.

Metabolism and functions of lipids in myelin

Rapid conduction of nerve impulses requires coating of axons by myelin sheaths, which are lipid-rich and multilamellar membrane stacks. The lipid composition of myelin varies significantly from other biological membranes. Studies in mutant mice targeting various lipid biosynthesis pathways have shown that myelinating glia have a remarkable capacity to compensate the lack of individual lipids. However, compensation fails when it comes to maintaining long-term stability of myelin. Here, we summarize how lipids function in myelin biogenesis, axon-glia communication and in supporting long-term maintenance of myelin. We postulate that change in myelin lipid composition might be relevant for our understanding of aging and demyelinating diseases. This article is part of a Special Issue titled Brain Lipids.

Nfasc155H and MAG are specifically susceptible to detergent extraction in the absence of the myelin sphingolipid sulfatide

Mice incapable of synthesizing the myelin lipid sulfatide form paranodes that deteriorate with age. Similar instability also occurs in mice that lack contactin, contactin-associated protein or neurofascin155 (Nfasc155), the proteins that cluster in the paranode and form the junctional complex that mediates myelin-axon adhesion. In contrast to these proteins, sulfatide has not been shown to be enriched in the paranode nor has a sulfatide paranodal binding partner been identified; thus, it remains unclear how the absence of sulfatide results in compromised paranode integrity. Using an in situ extraction procedure, it has been reported that the absence of the myelin sphingolipids, galactocerebroside and sulfatide, increased the susceptibility of Nfasc155 to detergent extraction. Here, employing a similar approach, we demonstrate that in the presence of galactocerebroside but in the absence of sulfatide Nfasc155 is susceptible to detergent extraction. Furthermore, we use this in situ approach to show that stable association of myelin-associated glycoprotein (MAG) with the myelin membrane is sulfatide dependent while the membrane associations of myelin/oligodendrocyte glycoprotein, myelin basic protein and cyclic nucleotide phosphodiesterase are sulfatide independent. These findings indicate that myelin proteins maintain their membrane associations by different mechanisms. Moreover, the myelin proteins that cluster in the paranode and require sulfatide mediate myelin-axon adhesion. Additionally, the apparent dependency on sulfatide for maintaining Nfasc155 and MAG associations is intriguing since the fatty acid composition of sulfatide is altered and paranodal ultrastructure is compromised in multiple sclerosis. Thus, our findings present a potential link between sulfatide perturbation and myelin deterioration in multiple sclerosis.

Ceramide glycosylation catalyzed by glucosylceramide synthase and cancer drug resistance

Glucosylceramide synthase (GCS), converting ceramide to glucosylceramide, catalyzes the first reaction of ceramide glycosylation in sphingolipid metabolism. This glycosylation by GCS is a critical step regulating the modulation of cellular activities by controlling ceramide and glycosphingolipids (GSLs). An increase of ceramide in response to stresses, such as chemotherapy, drives cells to proliferation arrest and apoptosis or autophagy; however, ceramide glycosylation promptly eliminates ceramide and consequently, these induced processes, thus protecting cancer cells. Further, persistently enhanced ceramide glycosylation can increase GSLs, participating in selecting cancer cells to drug resistance. GCS is overexpressed in diverse drug-resistant cancer cells and in tumors of breast, colon, and leukemia that display poor response to chemotherapy. As ceramide glycosylation by GCS is a rate-limiting step in GSL synthesis, inhibition of GCS sensitizes cancer cells to anticancer drugs and eradicates cancer stem cells. Mechanistic studies indicate that uncoupling ceramide glycosylation can modulate gene expression, decreasing MDR1 through the cSrc/β-catenin pathway and restoring p53 expression via RNA splicing. These studies not only expand our knowledge in understanding how ceramide glycosylation affects cancer cells but also provide novel therapeutic approaches for targeting refractory tumors.

Sulfatide storage in neurons causes hyperexcitability and axonal degeneration in a mouse model of metachromatic leukodystrophy

Metachromatic leukodystrophy is a lysosomal storage disorder caused by deficiency in the sulfolipid degrading enzyme arylsulfatase A (ASA). In the absence of a functional ASA gene, 3-O-sulfogalactosylceramide (sulfatide; SGalCer) and other sulfolipids accumulate. The storage is associated with progressive demyelination and various finally lethal neurological symptoms. Lipid storage, however, is not restricted to myelin-producing cells but also occurs in neurons. It is unclear whether neuronal storage contributes to symptoms of the patients. Therefore, we have generated transgenic ASA-deficient [ASA(-/-)] mice overexpressing the sulfatide synthesizing enzymes UDP-galactose:ceramide galactosyltransferase (CGT) and cerebroside sulfotransferase (CST) in neurons to provoke neuronal lipid storage. CGT-transgenic ASA(-/-) [CGT/ASA(-/-)] mice showed an accumulation of C18:0 fatty acid-containing SGalCer in the brain. Histochemically, an increase in sulfolipid storage could be detected in central and peripheral neurons of both CGT/ASA(-/-) and CST/ASA(-/-) mice compared with ASA(-/-) mice. CGT/ASA(-/-) mice developed severe neuromotor coordination deficits and weakness of hindlimbs and forelimbs. Light and electron microscopic analyses demonstrated nerve fiber degeneration in the spinal cord of CGT/ASA(-/-) mice. CGT/ASA(-/-) and, to a lesser extent, young ASA(-/-) mice exhibited cortical hyperexcitability, with recurrent spontaneous cortical EEG discharges lasting 5-15 s. These observations suggest that SGalCer accumulation in neurons contributes to disease phenotype.

Sulfatide promotes the folding of proinsulin, preserves insulin crystals, and mediates its monomerization

Sulfatide is a glycolipid that has been associated with insulin-dependent diabetes mellitus. It is present in the islets of Langerhans and follows the same intracellular route as insulin. However, the role of sulfatide in the beta cell has been unclear. Here we present evidence suggesting that sulfatide promotes the folding of reduced proinsulin, indicating that sulfatide possesses molecular chaperone activity. Sulfatide associates with insulin by binding to the insulin domain A8--A10 and most likely by interacting with the hydrophobic side chains of the dimer-forming part of the insulin B-chain. Sulfatide has a dual effect on insulin. It substantially reduces deterioration of insulin hexamer crystals at pH 5.5, conferring stability comparable to those in beta cell granules. Sulfatide also mediates the conversion of insulin hexamers to the biological active monomers at neutral pH, the pH at the beta-cell surface. Finally, we report that inhibition of sulfatide synthesis with chloroquine and fumonisine B1 leads to inhibition of insulin granule formation in vivo. Our observations suggest that sulfatide plays a key role in the folding of proinsulin, in the maintenance of insulin structure, and in the monomerization process.

Suppression of integrin expression and tumorigenicity by sulfation of lactosylceramide in 3LL Lewis lung carcinoma cells

To investigate the cellular functions of sulfated glycosphingolipids, we introduced the cerebroside sulfotransferase (CST) gene into J5 cells, a subclone of 3LL Lewis lung carcinoma cells. The J5 cells lack acidic glycosphingolipids but accumulate their common biosynthetic precursor, lactosylceramide. We established the stable CST transfectants, J5/CST-1 and J5/CST-2 clones, highly expressing sulfated lactosylceramide (SM3). Both clones exhibited more spherical morphology in comparison to mock transfectant, and their adhesiveness to fibronectin and laminin was significantly lower. The loss of cell-substratum interactions in these SM3-expressing cells could be attributed to decreased expression of integrins (alpha(5), alpha(6), and beta(1)) on the cell surface and their whole cellular levels. However, the levels of H-2K(b) and H-2D(b) antigens remained unchanged. Reverse transcriptase-polymerase chain reaction and Northern blot analyses for these integrins exhibited significant decrease of beta(1) gene expression in J5/CST-1 and 2, but there was no change in the levels of alpha(5) and alpha(6) transcripts. Deglycosylation by endoglycosidase H treatment clearly demonstrated that the precursor form of beta(1) integrin, possessing high mannose oligosaccharide chains, was preferentially decreased in the CST transfectants. These results demonstrate that endogenous SM3 negatively regulates beta(1) integrin expression at the transcriptional level, and the decrease of alpha integrin proteins in the CST transfectants was due to the post-transcriptional modification. We suggest the putative importance of the intracellular pre-beta(1) integrin pool for normal integrin maturation and subsequent function. Although the rates of cell proliferation in vitro for mock and CST transfectants were similar, tumorigenicity of J5/CST-1 and -2 cells inoculated into syngeneic C57/BL6 mice was greatly decreased or even absent. This was probably due to global loss of the efficient cell-matrix interactions, which are essential for the development of malignant tumors in vivo. Thus, we showed the evidence that cellular SM3 negatively regulates the cell-substratum interaction, resulting in the loss of tumorigenicity.

Expression cloning and characterization of NSIST, a novel sulfotransferase expressed by a subset of neurons and postsynaptic targets

Synapses are distinguished by localized concentrations of specific proteins, many of which bear the marks of posttranslational processing such as glycosylation and sulfation. One strategy to elucidate this posttranslational tailoring is to identify the enzymes that create these modifications. Monoclonal antibody 3B3 recognizes a carbohydrate-containing epitope expressed on dystroglycan and other constituents of Torpedo electric organ synaptic membranes. We used mAb 3B3 in an immunofluorescence-based expression-cloning method and isolated a cDNA clone conferring mAb-3B3 immunoreactivity to transfected COS cells. The deduced polypeptide has a predicted molecular weight of 51 kDa, a type II transmembrane topology, and four potential N-linked glycosylation sites. The polypeptide, which we term NSIST (nervous system involved sulfotransferase), shows extensive, although not complete, homology to a chondroitin-6-sulfotransferase and limited homology to other sulfotransferases. In NSIST-transfected COS cells, 35SO4 incorporation and chondroitin-sulfate-like immunoreactivity are increased. In vivo, NSIST occurs as a single 2.4 kb transcript abundant in Torpedo electric organ, moderately expressed in spinal cord and electric lobe, and undetectable in non-neural tissues. Immunohistochemistry shows that NSIST is expressed in a punctate distribution in the innervated portion of electrocytes. In the CNS, NSIST-like immunoreactivity is localized within the somas of motor neurons and neurons of the electromotor nucleus, whereas mAb-3B3 immunostaining is associated with cell surfaces and neuropil. Neuronal NSIST is therefore likely to exert its effects extracellularly; although NSIST is synthesized by neurons, its product, the 3B3 epitope, is found outside neuronal cell bodies. Our evidence indicates that NSIST participates in nervous system specific posttranslational modifications, perhaps including those at synapses.

Transport of proteolipid protein to the plasma membrane does not depend on glycosphingolipid cotransport in oligodendrocyte cultures

The possibility that transport of proteolipid protein (PLP) from its site of synthesis to the plasma membrane is dependent on cotransport with (sulfo)galacto-cerebrosides was investigated in primary cultured oligodendrocytes and Chinese hamster ovary (CHO) cells expressing PLP. Sulfation was inhibited by growing oligodendrocytes in the presence of a competitive inhibitor of this process, sodium chlorate. Under these circumstances, sulfatide synthesis was inhibited by 85%. Nevertheless, PLP was still delivered to the plasma membrane in quantitative amounts. Furthermore, when PLP was expressed in CHO cells, which normally synthesize very low amounts of galactosyl ceramide (GalCer) and no sulfatide, PLP was transported to the plasma membrane. Moreover, in CHO cells coexpressing PLP and ceramide galactosyl transferase, PLP cell surface labeling was unaltered. Noting that it has been demonstrated that proteins destined for the apical surface of epithelial cells colocalize with glycolipid-enriched microdomains, we isolated detergent-insoluble membrane complexes from cultured oligodendrocytes. We found, however, that most of the PLP is present in the detergent-soluble fraction and, furthermore, that PLP could not be chased into or out of the insoluble fraction. Taken together, these data make it very likely that in oligodendrocytes PLP transport takes place irrespective of the presence of glycosphingolipids GalCer and sulfatide.

Maintenance of membrane sheets by cultured oligodendrocytes requires continuous microtubule turnover and Golgi transport

Oligodendrocytes in murine shakeoff cultures elaborate extensive membrane sheets containing networks of microtubules. Several membrane components, including proteolipid protein (PLP) and sulfatide, are transported through the Golgi en route to the plasma membrane or myelin (1,2). This transport is essential for membrane assembly, but its role in continuing maintenance of the sheets is not known. We examined the stability of the membrane sheets following microtubule stabilization with taxol or block of transport into the Golgi with brefeldin A. Within one to three hours, both agents had marked effects on the membrane sheets. While some oligodendrocytes maintained regions of normal membrane sheets, many showed retraction of the sheets, with the majority now exhibiting multiple processes rather than sheets. The distribution of sulfatide, PLP and tubulin in cell bodies, processes and sheets was altered in treated cells, as analyzed by immunocytochemical staining with antibodies to these components. The Golgi apparatus also showed reorganization in the presence of taxol, as visualized by binding of wheat germ agglutinin, a lectin with high affinity for distal Golgi vesicles. All of these effects were reversible when the agents were removed after 3 hours. Thus, maintenance of membrane sheets by oligodendrocytes in culture is a dynamic process, requiring ongoing microtubule turnover and transport of molecules through the Golgi.

Basis for phospholipid incorporation into peripheral nerve myelin

To characterize the mechanism(s) for targeting of phospholipids to peripheral nerve myelin, we examined the kinetics of incorporation of tritiated choline-, glycerol-, and ethanolamine-labeled phospholipids into four subfractions: microsomes, mitochondria, myelin-like material, and purified myelin at 1, 6, and 24 h after precursors were injected into sciatic nerves of 23-24-day-old rats. As validation of the fractionation scheme, a lag (> 1 h) in the accumulation of labeled phospholipids in the myelin-containing subfractions was found. This lag signifies the time between synthesis on organelles in Schwann cell cytoplasm and transport to myelin. In the present study, we find that sphingomyelin (choline-labeled) accumulated in myelin-rich subfractions only at 6 and 24 h, whereas phosphatidylserine (glycerol-labeled) and plasmalogen (ethanolamine-labeled) accumulated in the myelin-rich fractions by 1 h. The later phospholipids accumulate preferentially in the myelin-like fraction. These results are consistent with the notion that the targeting of sphingomyelin, a lipid present in the outer myelin leaflet, is different from the targeting of phosphatidylserine and ethanolamine plasmalogen, lipids in the inner leaflet. These findings are discussed in light of the possibility that sphingomyelin targeting is Golgi apparatus based, whereas phosphatidylserine and ethanolamine plasmalogen use a more direct transport system. Furthermore, the routes of phospholipid targeting mimic routes taken by myelin proteins P0 (Golgi) and myelin basic proteins (more direct).

Elevated serum level of glycolipid sulfotransferase in patients with hepatocellular carcinoma

Activity of glycolipid sulfotransferase (cerebroside sulfotransferase) in serum was elevated in 21 (33%) of 63 patients with hepatocellular carcinoma (HCC, mean +/- S.E., 349 +/- 32 pmol/ml per h, n = 63, P less than 0.001) compared to healthy subjects (172 +/- 12, n = 85). Ho significant elevation of the sulfotransferase level was observed in liver cirrhosis (219 +/- 28, n = 10) in which many of biochemical HCC markers increase concomitantly. The elevation of sulfotransferase was independent of the production of alpha-fetoprotein and of aminotransferase levels in HCC, providing complementary value for alpha-fetoprotein-negative HCC cases. However, the sulfotransferase levels (234 +/- 21, n = 32, P less than 0.01) in sera from patients with renal cell carcinoma, in whose involved tissues the enzyme was demonstrated to increase markedly, were less than in HCC.

Novel NGF-induced proteins in PC12 cells: immunological evidence for their presence in brain nerve endings using a single monoclonal antibody

A monoclonal antibody, S-11D9, detected a group of novel polypeptides whose expression was induced 6 hr after incubation of PC12 cells with nerve growth factor. The antigens also were visualized by immune precipitation and Western blotting in synaptic vesicles, clathrin-coated vesicles, and synaptic plasma membrane prepared from bovine brain. A large polypeptide was detected on the synaptic plasma membrane; an intermediate size protein was visualized on the plasma membrane and on both synaptic and clathrin-coated vesicles, while a smaller molecule was found only on brain Golgi-enriched membrane preparations. Immunofluorescence labeling with S-11D9 on nerve growth factor-stimulated PC12 cells showed the antigens distributed in the cytoplasm and concentrated in discrete areas on the tip of most neurites. The particular distribution of these proteins in vesicles and synaptic plasma membrane and the finding that the different antigens share a common epitope recognized by a single monoclonal antibody open the possibility that these molecules are related markers for organelle transport pathways in nerve cells.

Presence and characterization of glycolipid sulfotransferase in human cancer serum

Sulfotransferase, which catalyzes sulfation of the carbohydrate of galactosylceramide (GalCer) and is localised in the Golgi membrane of cells, was assayed for activity in human serum. To do this, an organic solvent was added to the incubated reaction mixture containing GalCer as an acceptor and phosphoadenosine phospho[35S]-sulfate as a donor of sulfate to dissociate the synthesized sulfolipid from serum protein. This was followed by isolation of the sulfolipid on an anion-exchange column. Through this procedure, human serum was found to contain sulfotransferase activity. The serum enzyme was activated by Mn2+. Km values of the enzyme for GalCer and 'active sulfate' were 4.6 microM and 5.2 microM, respectively. The enzyme activity was assayed in sera of cancer patients. The serum activity (mean +/- SE, 0.27 +/- 0.027 pmol.microliter-1.h-1) in renal cell carcinoma patients, whose activity has been demonstrated to be elevated, was significantly (P less than 0.005) increased compared to that of the normal control (mean +/- SE, 0.18 +/- 0.0014 pmol.microliter-1.h-1) and of other urological tumors examined.

Galactosylceramide sulfotransferase, arylsulfatase A and cerebroside sulfatase activity in different regions of developing rat brain

The in vivo metabolism of sulfatides was studied in spinal cord and cerebral cortex of developing rat pups. Developmental changes in the rate of sulfolipid synthesis were measured after the intraperitoneal injection of 35SO4(2-). We also measured the accumulation of sulfatides, as well as the profiles of cerebroside sulfotransferase, cerebroside sulfatase and arylsulfatase A in both brain regions as a function of postnatal development. The accumulation of sulfatides was higher in spinal cord than in cerebral cortex. In addition, sulfatide metabolism was more active in spinal cord. In both brain regions, the developmental pattern of 35SO4(2-) incorporation into sulfolipids was closely correlated to the activities of cerebroside sulfotransferase and of arylsulfatase A. The activity of these enzymes was initially low, increased during the period of active myelination and declined thereafter. However, the activity of cerebroside sulfatase, measured with its physiological substrate, [35S]sulfatide, increased during development and did not decline. An explanation for the difference between the developmental profiles of the arylsulfatase A and cerebroside sulfatase reactions (which are supposed to be catalysed by the same enzyme) is proposed.

Decreased metabolism of cerebrosides and sulfatides in rat sciatic nerve after intraneural injection of colchicine

To obtain an understanding of the importance of the neuronal cytoskeleton in Schwann cell metabolism, an antimicrotubular agent (colchicine) was injected into the rat sciatic nerve 24 or 48 h before incubation of the nerve with labeled precursor: [35S]sulfate, [14C]galactose, or [3H]-galactose. Colchicine inhibited the incorporation of 35S radioactivity into sulfatides and, to a lesser extent, into proteins. With galactose as the radioactive precursor, synthesis of cerebrosides was reduced by colchicine injection, whereas incorporation of radioactivity into phosphatidylserine and phosphatidylcholine increased. Intraneural injection of lumicolchicine had no effect. The effects of colchicine on the metabolism of the Schwann cell are discussed in relation to its action on microtubules.

Subcellular distribution of UDP-galactose:ceramide galactosyltransferase in rat brain oligodendroglia

Oligodendrocytes isolated from 18-19-day-old rat brain were homogenized in 0.32 M sucrose. The homogenate was centrifuged at 100,000 g for 50 min in a gradient containing 0.8, 1.05, and 1.3 M sucrose. Three discrete bands were obtained at the interfaces 0.32-0.8 (F1), 0.8-1.05 (F2), and 1.05-1.3 M (F3). The distribution of UDP-galactose:ceramide galactosyltransferase (CgalT) activity in each fraction was measured using liposomes containing normal fatty acid-containing ceramides (NFA-CgalT activity) or 2-hydroxy fatty acid-containing ceramides (HFA-CgalT activity). Although detection of both CgalT activities was possible in all fractions, HFA-CgalT activity was enriched in F1 and F2 fractions, which also showed an enrichment of Golgi and endoplasmic reticulum markers, respectively. It is interesting that NFA-CgalT activity was significantly enriched in the F2 fraction. These results suggest that hydroxylated and nonhydroxylated galactocerebrosides may be synthesized at different intracellular locations.

Studies on the submicrosomal fractions of bovine oligodendroglia: lipid composition and glycolipid biosynthesis

Oligodendroglia were isolated from bovine brain, and a "crude" microsomal fraction obtained from cell homogenates was subfractionated into myelin (MP), plasma membranes (PM), Golgi (GF), smooth (SER) and rough (RER) endoplasmic membranes using discontinuous-sucrose gradient centrifugation. The submicrosomal fractions were characterized by ultrastructural examination and analysis of the specific organelle markers. The myelin and plasma membrane rich fractions contained characteristically the highest amounts of the lipid with lower mole percentages of total phospholipids and phosphatidylcholine, and higher concentrations of phosphatidylethanolamine (+ plasmalogens), cholesterol and galactolipids. Considerable amounts of the typical myelin galactolipids (galacto-cerebrosides, sulfatides and monogalactosyl diglycerides) were also found in the Golgi fraction (GF). The GF fraction had the greatest enrichment of glycolipid-forming galactosyltransferases, and the distribution of these enzymes correlated well with that of the Golgi marker enzymes. The results give evidence that intracellular Golgi apparatus of oligodendroglia is rich in the myelin-specific lipids, and suggest its involvement in the synthesis and processing of myelin lipids.

Synthesis and transport of cerebrosides and sulfatides in rat brain during development

Synthesis and transport of nonhydroxy fatty acid (NFA)- and hydroxy fatty acid (HFA)-containing ceramides, cerebrosides, and sulfatides were studied in vivo in rat brain during development. After an intracerebral injection of [3H]serine, incorporation into these lipids of microsomal and myelin membranes was analyzed after HPLC. Distribution of amounts and incorporation of radioactivity were also determined in individual molecular species of these lipids. The results showed that HFA-ceramides and long-chain NFA-ceramides have small pool sizes and rapid turnover rates in the microsomal membranes and are preferentially utilized for the synthesis of long-chain (greater than or equal to 20:0) HFA- and NFA-galactocerebrosides of both microsomal and myelin membranes. Glucocerebrosides are not expressed in myelin and their synthesis in microsomal membranes is predominant before the onset of myelination. With development, synthesis and accumulation of HFA-cerebrosides increase over NFA-cerebrosides in both microsomal and myelin membranes. In myelin, incorporation of radioactivity into HFA-cerebrosides is even higher than that expected by transport alone from microsomal membranes and it is possible that part of the HFA-cerebrosides in myelin could be due to de novo synthesis by myelin itself. The amount of NFA- and HFA-sulfatides is about equal, both in myelin and microsomal membranes, and this relative proportion does not change with development. Similar relative rates of incorporation of radioactivity into sulfatides of microsomal and myelin membranes are consistent with the notion that both NFA and HFA sulfatides are synthesized in the microsomal (Golgi) membranes and are transported to myelin.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulated galactolipid synthesis and cell surface expression in Schwann cell line D6P2T

Clonal cell line D6P2T, subcloned from an ethylnitrosourea-induced tumor line D6 of the rat peripheral nervous system, has been characterized with particular attention to galactolipid metabolism. Galactosylcerebroside and sulfatide synthesis and expression on the cell surface are highly regulated in D6P2T cells by mechanisms involving serum- and cyclic AMP-mediated pathways. These cells also express 2',3'-cyclic nucleotide 3'-phosphohydrolase (Wolfgram protein W1a) and laminin. In contrast, myelin basic protein and antigen HNK-1 were not detected. Line D6P2T appears to be a semi-differentiated Schwann cell model, which offers interesting possibilities for studies of galactolipid synthesis, transport, and sorting.

Postnatal D2-CAM/N-CAM sialylation state is controlled by a developmentally regulated Golgi sialyltransferase

Golgi-enriched fractions have been isolated from rat brain of increasing postnatal age and defined by electron microscopy and distribution of marker enzymes. The expression of sialyltransferase activity associated with these fractions has been demonstrated to developmentally decrease and this appeared to be, in part, dependent on endogenous competitive inhibition. The developmental regulation of this activity paralleled the sialylation state of the neural cell adhesion molecule (D2-CAM/N-CAM) and could be demonstrated to be capable of endogenously sialylating this protein in the isolated Golgi fractions. In 12-day-old animals the majority of the transferred [14C]sialic acid was found to be associated with the high-molecular-weight [greater than 200 kilodaltons (kd)] form of D2-CAM/N-CAM, indicative of the protein having been heavily sialylated. Sialylation of the individual D2-CAM/N-CAM polypeptides was also demonstrated in both 12-day and adult animals and transfer was evident only in the 180-kd and 115-kd components and not in the 140-kd component. In contrast, Golgi-enriched fractions prepared from adult animals showed little capability of heavily sialylating D2-CAM/N-CAM to any significant extent.

Biochemical correlates of myelination in brain and spinal cord of mice heterozygous for the jimpy gene

Brain and spinal cord of female mice heterozygous for the jimpy gene were analyzed during development for activity of ceramide galactosyl transferase (CGT) and for levels of myelin basic protein (MBP). CGT activity was low at 13-14 days in brains of heterozygous jimpy females but showed normal levels by 31-36 days, in agreement with our earlier study of this enzyme. In cord, CGT activity was normal or slightly above normal at all ages studied, from 13-14 days into adulthood. In both brain and cord, decreased levels of MBP were observed at 13 days; by 100 days, amounts of MBP approached normal levels. Proven female carriers of the jimpy gene also showed normal levels of CGT activity, MBP, and isolated myelin at 200-250 days of age in both brain and cord. These biochemical findings agree with previous morphologic measurements in cord demonstrating deficits in myelin at early ages but compensation by 100 days. Our results show that compensation occurs earlier in cord than in brain and that levels of MBP show a closer correlation than CGT activity with amounts of myelin, as measured by either morphometric analysis or direct isolation.

Myelin-associated galactolipids in primary cultures from dissociated fetal rat brain: biosynthesis, accumulation, and cell surface expression

Galactolipid metabolism was investigated as a function of development in primary cultures initiated from 19-21-day-old dissociated fetal rat brain. Significant amounts of galactocerebrosides, sulfatides, and monogalactosylglycerides were synthesized and accumulated by 8 days in culture. Thereafter the synthetic rates and levels of these galactolipids increased rapidly, reaching maximal values approximately 22-29 days in culture. Galactolipids containing nonhydroxy or 2-hydroxy fatty acid were both synthesized at approximately equal rates. The initial rates of synthesis, investigated at 15, 29, and 50 days in culture, were three- to fivefold higher for galactocerebrosides than for sulfatides and two- to threefold higher than for monogalactosylglycerides. The total number of cells staining with antisera against galactocerebroside of sulfatide also increased very rapidly between 8 and 22 days in culture, reaching levels of 4-5 million cells per seeded fetal brain. The amount of galactocerebroside or sulfatide per cell stained with the corresponding antiserum increased severalfold from 10 to 27 days in culture and remained high until at least 36 days in culture (the latest time point examined). Thus, the temporal expression of galactolipid accumulation in the cell cultures was comparable to that occurring in rat brain, but some important quantitative reductions in the levels of accumulation per cell in culture were noted. In addition, in contrast to normal brain in which galactolipid synthetic rates are reduced after the period of most active myelination, in culture both synthesis and turnover of these galactolipids remained high, suggestive of a partial arrest in myelin maturation.

Purification and characterization of galactocerebroside sulfotransferase from rat kidney

Galactocerebroside sulfotransferase (EC 2.8.2.11) was purified to apparent homogeneity from rat kidneys. The purified protein is stable at -20 degrees C, and has an estimated molecular weight of 64,000 and a pI of 5.1. In contrast to other known sulfotransferases, the enzyme appears not to require divalent metal ions for activity. The Km for the donor, 3'-phosphoadenosine 5'-phosphosulfate, is 5.2 microM. Structural studies on this "active" sulfate donor show the requirement of a phosphate group at the 3' position of the ribose moiety. Modification of the amino group at either the 6 or 8 position on the purine ring renders the corresponding compounds poor substrates. Both galactosylceramide and lactosylceramide are effective acceptors for this enzyme, while galactosylsphingosine and galactosylglycerolipids are sulfated only poorly, suggesting that the in vivo sulfation of these glycolipids is carried out by different sulfotransferases. The active site of the enzyme contains arginine residues which appear to be important in binding the sulfate donor. The enzyme protein is hydrophobic and binds 0.17 mg [3H]Triton X-100/mg protein. The purified enzyme contains bound lipids, consisting primarily of cholesterol and phosphatidylcholine. The lipid environment affects the activity of the enzyme which, in turn, regulates the sulfation of glycolipids.

Isolation and characterization of an enriched Golgi fraction from neurons of developing rat brains

We report a method for the isolation of enriched fractions of intact Golgi apparatus from neurons of 10- to 12-day-old rat brains. Neurons were prepared according to a modified method of Farooq and Norton [J. Neurochem. 31, 887-894 (1978)]. Golgi-enriched fractions were obtained after centrifugation of postmitochondrial supernatants in a discontinuous sucrose gradient. Golgi fractions 1 and 2, recovered at the interfaces of 28-34% and 34-36% sucrose densities, respectively, were examined with morphometric and enzymatic methods. Morphometric analyses showed that 21-34% of fraction 1 and 11-29% of fraction 2 consisted of intact Golgi apparatus. Lysosomes, mitochondria, ribosomes, and rough endoplasmic reticulum contaminated fraction 1 (6-10%) and fraction 2 (14-26%). Golgi fraction 1 showed a 25- to 65-fold enrichment over neurons of UDP Gal:GlcNAc galactosyltransferase, CMP-sialic acid:lactosylceramide sialyltransferase, and PAPS:cerebroside sulfotransferase activities. Golgi fraction 2 showed a 8- to 23-fold enrichment over neurons of the activities of the above glycolipid- and glycoprotein-synthesizing enzymes. The activities of the possible marker enzymes rotenone-insensitive NADH-cytochrome c reductase, succinate-cytochrome c reductase, and arylsulfatase were low or minimally elevated in the Golgi fractions. A sevenfold enrichment of Na+, K+-ATPase activities was found in the Golgi fractions. This is consistent either with significant plasma membrane contamination or with the presence of this enzyme in the neuronal Golgi apparatus.

Neonatal malnutrition in the rat affects the delivery of sulfatides from microsomes and their entry into myelin

Brain slices from 18 day old normal and malnourished rats were incubated in the presence of [35S]sulfate to explore its incorporation into sulfatides of a total brain homogenate and the appearance of labeled sulfatides in different subcellular fractions. While the incorporation of label into sulfatides of the total homogenate was similar in both groups of animals, in subcellular fractions separated on a linear sucrose density gradient, labeling of sulfatides in malnourished animals was relatively higher in the region corresponding to the microsomal fraction. Time course incorporation and pulse-chase experiments were carried out to explore the kinetics of labeling of microsomal and myelin sulfatides. In pulse-chase experiments, normal controls showed a decrease in the specific radioactivity of sulfatides in the microsomal fraction after the chase, which was not observed in malnourished animals, while the appearance of labeled sulfatides in the myelin fraction of the latter group of animals was found to be lower than in normals. These results suggest that in neonatal malnutrition there is a defect in the transport of de novo synthesized sulfatides towards myelin or/and a problem in the assembly of these lipids into the myelin membrane.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolism of cerebrosides and sulfatides in subcellular fractions of developing rat brain

Previous studies on myelinating rat brain indicated that microsomes, Golgi-enriched and cytosol fractions may process galactolipids destined for myelin. To extend these findings we labeled brain galactolipids in vivo and determined the specific radioactivity of cerebrosides and sulfatides in several subcellular fractions. 17-day-old rats were treated by intracranial injection with [14C]galactose 60 min prior to and [3H]galactose 15 min prior to killing. Subcellular fractions were prepared from brain stem, and concentrations of cerebrosides and sulfatides were determined, their radioactivity measured and the 3H/14C ratio compared. Our results showed that the heavier Golgi-enriched fraction (designated Fraction 2) is unique in its low galactolipid content and high specific radioactivities of cerebrosides and sulfatides. The low ratio of the specific activity of cerebroside to that of sulfatide in Fraction 2 compared to other fractions indicates that it may be the site of most rapid conversion of newly synthesized cerebrosides to sulfatides. The specific radioactivities of cerebrosides and sulfatides in cytosol are intermediate between those in Golgi-enriched Fraction 2 and microsomes and those in myelin, consistent with the role postulated for cytoplasmic elements in the transport of cerebrosides and sulfatides to myelin.

Effects of monensin and colchicine on myelin galactolipids

Monensin and colchicine have been used in a variety of systems to disrupt functioning of the Golgi apparatus and transport of Golgi-derived vesicles to the plasma membrane. In this study the effects of monensin and colchicine on the synthesis of cerebroside and sulfatide and their appearance in myelin were examined to determine whether these myelin components are processed through the Golgi apparatus. Brain slices from rats 17 days old were incubated with [3H]galactose and [35S]-sulfate to label cerebroside and sulfatide. Myelin was isolated on sucrose density gradients. Fractions highly enriched in cerebroside and sulfatide were prepared from homogenates and myelin fractions by lipid extraction, alkaline methanolysis, and in some cases TLC. Monensin at 0.1 microM had no significant effect on synthesis of these galactolipids as measured by incorporation of [3H]-galactose into cerebroside or [35S]sulfate into sulfatide in homogenates. However, appearance of [35S]sulfatide in the myelin fraction was reduced to 49% of control, while appearance of [3H]cerebroside was not significantly reduced. Colchicine from 1 mM to 0.1 microM had effects similar to monensin, that is, appearance of [35S]sulfatide in myelin was depressed, but again [3H]cerebroside was not affected. Incorporation of [35S]sulfate into sulfatide in homogenate was 93% of control, while appearance of [35S]sulfatide in the myelin fraction was depressed to 58% of control. The inhibition of appearance of sulfatide in myelin by colchicine and monensin is consistent with the view that sulfation of cerebroside occurs in the Golgi and that sulfatide is transported via Golgi-derived vesicles to the forming myelin membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Phospholipid biosynthesis in myelin: presence of CTP:phosphoethanolamine cytidylyltransferase in purified myelin of rat brain

Highly purified myelin from rat brain was previously shown to contain the ethanolaminephosphotransferase which completes the synthesis of phosphatidyl ethanolamine. We have now obtained evidence for the presence in myelin of CTP:phosphoethanolamine cytidylyltransferase, the enzyme catalyzing formation of CDP-ethanolamine. Myelin was isolated by two different procedures, one based on the Norton-Poduslo method and the other involving repetitive gradients with osmotic shocking deferred to the end. The fact that activity remained constant through all but the earliest steps suggested that the enzyme is intrinsic to myelin. Comparison of subcellular fractions revealed that approximately half the total activity was in the supernatant, the remainder being distributed among the particulate fractions. Relative specific activity of myelin was 27-31% that of microsomes, thus eliminating the possibility of appreciable contamination by the latter. The possibility of adsorption of the soluble enzyme by myelin was rendered unlikely by retention of activity after washing the myelin with buffered sodium chloride or sodium taurocholate. Furthermore, relative specific activity of the cytidylyltransferase was 10-fold higher than that of lactate dehydrogenase (a cytosolic marker) in myelin. The apparent Km for CTP was approximately the same for myelin and microsomes, but that for phosphoethanolamine was significantly higher for myelin.

Bulk separation and long-term culture of oligodendrocytes from adult pig brain. II. Some biochemical data

Oligodendroglial proteins labeled with radioactive amino acids were subjected to one- and two-dimensional polyacrylamide electrophoresis. Bands comigrating with myelin proteins, the basic protein (MBP), the proteolipid protein (PLP), and the Wolfgram protein (WP) doublet, were detected by Coomassie Blue staining and by autoradiography. The identity of the MBP and WP in the cellular material is evidenced by immunoblotting with specific antibodies. A comparative study of myelin samples from rat and pig CNS reveals that WP can be detected immunochemically in both species. Different protein patterns, however, are observed. Three protein bands are found with antibodies against the myelin-associated glycoprotein (MAG). The high-molecular-weight component prevails in pig myelin, whereas the medium-molecular-weight component is predominant in rat myelin. Moreover, two protein bands, of molecular weights 35,000 and 33,000 (Ol 1 and Ol 2), are present in high amounts in oligodendroglial particulate material but are not detectable in myelin. These oligodendroglial characteristic proteins are not species-specific, since they are found in preparations of cat oligodendrocytes as well. Activities of cerebroside sulfotransferase (EC 2.8.2.11) are low in freshly isolated cells and increase during the first week of culture. A reverse course of enzyme activities is observed with 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37). Values reach a minimum about day 5 in culture and recover their initial values. At day 10 they remain stable until the end of the third week of the culture period.

Characterization of brain synaptic vesicle phospholipase A2 activity and its modulation by calmodulin, prostaglandin E2, prostaglandin F2 alpha, cyclic AMP, and ATP

Brain synaptic vesicle phospholipase A2 (PLA2) activity was characterized. It is Ca2+-dependent and has a pH optimum of 9.0. The enzyme has a Km of 60 microM and a Vmax of 2.0 nmol/mg/h. Calmodulin, prostaglandin F2 alpha, and cAMP, and ATP all increased the Vmax of the enzyme. Prostaglandin E2 inhibited the Vmax in the presence or absence of calmodulin. Light-scattering techniques in conjunction with phase-contrast and electron microscopy demonstrated that an increase in Vmax of PLA2 was correlated with synaptic vesicle aggregation, lysis, and possible fusion. In vitro synaptic vesicle-vesicle association that was stimulated by conditions that increased PLA2 activity could be diminished when synaptic vesicles were preincubated with PLA2 inhibitors. It is suggested that endogenous synaptic vesicle PLA2 activity may be an important mechanism underlying Ca2+-mediated neurotransmitter release.

Lipid metabolism of isolated oligodendrocytes maintained in long-term culture mimics events associated with myelinogenesis

Oligodendrocytes isolated from ovine white matter according to a published procedure [Szuchet, S., Stefansson, K., Wollmann, R. L., Dawson, G. & Arnason, B. G. W. (1980) Brain Res. 200, 151-164] were cultured for up to 35 days and their capacity to incorporate precursors into lipids was investigated. At various times, cultures were double labeled with [3H]glycerol/[14C]acetate or [3H]galactose/35SO2-4. The cells were harvested 72 hr later and lipids were fractionated using standard procedures. The time course of incorporation for each precursor was distinct. In the days after attachment to substratum, oligodendrocytes preferentially incorporated [3H]glycerol into phospholipids and [14C]acetate into cholesterol while uptake of 35SO2-4 and [3H]galactose into glycolipids was modest. A switch in phospholipid metabolism from preferential incorporation into phosphatidylcholine to incorporation into phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol occurred at about the 10th day in vitro. After 20 days, uptake of [3H]glycerol into phospholipids and [14C]acetate into cholesterol had stabilized but incorporation of 35SO2-4 into glycolipids had increased. 35SO2-4 incorporation into glycolipids was even greater at 35 than at 20 days. Uptake of [3H]galactose did not change over time. An attempt was made to correlate changes in lipid metabolism with morphologic developments. High incorporation into phospholipids and cholesterol coincided in time with the extensive membrane synthesis required for cell attachment and process extension. Differentiation of these newly formed membranes, as assessed by the incorporation of myelin-characteristic glycolipids, galactocerebrosides, and sulfatides, occurred at a time when an intricate network of processes had already been established. The sequence of metabolic events observed in vitro parallels that observed at the onset of myelinogenesis in vivo. We postulate that mature oligodendrocytes can reenact those early events associated with myelinogenesis.

Topography of cerebroside sulfotransferase in Golgi-enriched vesicles from rat brain

Cerebroside sulfotransferase (CST) catalyzes the final step in the synthesis of sulfatide (sulfogalactocerebroside) by transferring the sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to galactocerebroside. Orientation of CST was studied in vesicles enriched in this enzyme obtained from 21-d-old rat brain. Several lines of evidence indicate that CST is located on the luminal side of these vesicles. (a) Sulfation of endogenous galactocerebroside occurred in vesicles only in the presence of a detergent to render the membranes permeable to exogenous PAPS. (b) There is a pool of latent enzyme within the vesicle, which is released by Triton X-100. (c) CST is not destroyed by trypsin unless the vesicle membranes are first made permeable by Triton X-100. (d) Glycolipid substrate, when covalently attached to agarose beads, was not sulfated unless the enzyme was solubilized. These results are similar to those obtained with thiamine pyrophosphatase, which is known to be located within the lumen of the vesicles. This study establishes that an enzyme synthesizing a complex glycolipid is localized within Golgi-enriched vesicles. Since the product of the CST reaction must also be localized to the luminal side of the vesicles, it is most likely that sulfatide is located at the intraperiod line (outer layer) of myelin. The orientation of CST within the vesicle provides a mechanism for the asymmetrical assembly of glycolipids in bilayers.

Ganglioside-basic protein interaction: protection of gangliosides against neuraminidase action

The ability of acidic phospho- and sphingolipids to interact with basic proteins was studied by double diffusion analysis. The phospholipids, tri- and diphosphoinositide, and the sphingolipid, sulfatide, interacted with myelin basic protein as evidenced by precipitin line formation. Of the sialoglycosphingolipids (gangliosides) tested, only the myelin-specific monosialoganglioside, GM4, formed a precipitin line with myelin basic protein. In addition, myelin basic protein retarded the activity of Clostridium perfringens neuraminidase against GM4 and the disialoganglioside, GD1b. Examination of purified rat brain myelin suggested the presence of a neuraminidase activity intrinsic to myelin. This finding, in concert with ganglioside-myelin basic protein complexes which selectively protect against neuraminidase, may provide a physiological explanation for the simplified ganglioside pattern found in myelin.

Gangliosides and proteins in developing chicken brain myelin

Ganglioside and protein content of chicken brain myelin have been studied as a function of development and maturation. Ganglioside concentration remained relatively constant at approximately 225-266 micrograms sialic acid per 100 mg myelin, from 17-day-old embryos to 540-day-old adults. The ganglioside distributional pattern was also constant, GM1 and GM4 each accounting for approximately one-third of total sialic acid. These properties are contrasted with those of mouse and rat brain myelin which previously showed enrichment of GM1 at early stages of myelination and appearance of GM4 at a later stage of maturation. In an earlier study of the mouse total myelin gangliosides doubled in concentration between 3 and 5 weeks of age and full maturity. Myelin proteins of the chicken also remained relatively constant in concentration and distributional pattern during development, although the percentage of basic protein increased somewhat during the first few weeks after hatching. Correlations were observed between molar concentrations of basic protein and various gangliosides, particularly the monosialo types.