Neurochem. ht. Vol. 31, No. 1, PP. 105–111, 1997 @ Pergamon ~ 1997 El&ier Science Ltd PII: SO1974186(96)OO12f+3 Printed in Great Britain.All rightsreserved O197VO186/97 $17.00+0.00 LIGHTEXPOSURESTIMULATESTHEACTIVITY OF GANGLIOSIDEGLYCOSYLTRANSFERASESOF RETINA GANGLION CELLS DANIELA F. BUSSOLINO,MARIO E. GUIDO and BEATRIZ L. CAPUTTO* CIQUIBIC(CONICET) DepartamentodeQuhnicaBiologica, FacultaddeCienciasQrdmicas, UniversidadNacionaldeCordoba,Cordoba,Argentina (Received27 May 1996; accepted 14 October 1996) Abstract-Inchickssubmitted to lightstimulation, thesynthesisofgangliosides oftheretinaganglioncell increaseswithrespectto chicksmaintainedin thedark. In an attempt to elucidate if the activationof glycosyltransferases participatesin theestablishment of theselight~ark differences detected in vivo, we examinedthe activityof a key gangliosideglycosyltransferase, the GalNAc-T (N-acetylgalacto- saminyltransferase) that converts GM3 to GM2, in the retina ganglion cells isolated from light and dark exposed chicks. We found that GalNAc-T and other glycosyltransferases are active in these ganglion cell preparations; the kinetic parameters for GalNAc-T were similar to those previously reported for chick retina. The other glycosykra~sferase activites assayed were the galactosyltransferase (Ga~T2) that converts GM2 to GM1 and the N-acetylneuraminykransferase (Sialyl-Tl) that converts lactosylceramide to GM3. The three glycosyltransferase activities were higher in the ganglion cell preparations obtained from chicks exposed to light compared to those maintained in the dark. For the GalNAc-T activity, the differences disappear when the cell preparations are sonicated or if the assays are carried out in the presence of detergents or if the end product of the reaction is added to the incubates. The results indicate that the activation of the glycosyltransferases is part of the phenomenon required for cells to achieve the precise rate of synthesis of gangliosides needed in viuo. ~ 1997 Elsevier Science Ltd INTRODUCTION The regulation of the biosynthesis of gangliosides is a processpoorly understood up to the present. During development, the pattern of gangliosidesvaries very precisely (Rosner, 1994;Yu, 1994).This pattern is probably achieved by controlling the activity of key glycosyltransferases catalyzing their biosynthesis (Panzetta et al., 1987;Yu et al., 1988)and the levels of donor sugar nucleotides(Martina et al., 1995),by *Authortowhomallcorrespondence shouldbeaddressed. Abbreviations: GalNAc-T, UDP-N-acetylgalactosarnine: (N-acetylneuraminyl)galactosyl-ghrcosykeramide (GM3) ~1+4 N-acetylgalactosaminyl transferase (EC 2.4.1.92); Gal-T2, UDP-galactose:N-acetylgalactosarninyl (N-ace- tylneuraminyl) galactosylglucosylceramide (GM2) /11~ 3 galactosyltransferase (EC 2.4.1.62); Sialyl-Tl, CMP-N- acetylneuraminate:lactosylceramide rt2~3 N-acetylneur- aminyltransferase (EC 2.4.99); CMP-NeuNAc, cytidine 5’-monophospho-N-acetylneuraminic acid; UDP- GalNAc, uridine 5’-diphospho-N-acetylgalactos~ine; UDP-Gal, uridine 5’-diphospho-galactose. Gangliosides are named according to Svennerholm (1963). the action of endogenous inhibitors (Albarracin et al., 1988;Constantine-Ceccarini and Suzuki, 1978; Kivatinitz et al., 1995;Quiroga et al., 1984)and by the compartmental organization of the biosynthetic machinery (Maxzrid et al., 1995).However, once the definite pattern of gangliosideshas been established in the differentiated neurons, other regulatory con- straints must operate to attain the quantity and qual- ity of gangliosidescharacteristic of each differentcell type (Caputto, 1991). It has been found that animals subjectedto different learning paradigms or to different illumination con- ditions show changes in the labelling of their brain gangliosides (Dunn and Hogan, 1975; Irwin and Samson,1971;Maccioni et al., 1971,1974;Savakiand Levis, 1977).Differentexperimentalapproaches have beenused to postulate a negativefeedbackmechanism through which GM2 or other end-product gan- gliosidesregulatetheir ownrate of synthesisin normal (Nores and Caputto, 1984;Richardson et al., 1977, Shukla et al., 1991;Yusuf et al., 1987)and neoplastic cells(Merrit and Morre, 1980).This regulatory mech- 105