Full text in pdf format

Nucleolar subunits in the salivary gland nuclei of Sciara ocellaris (Diptera, Sciaridae)

Eliana M.B. Dessen; André Luiz P. Perondini

Departamento de Biologia, Instituto de Biociências-USP, Caixa Postal 11461. 05499 São Paulo, SP, Brasil

ABSTRACT

In situ hybridization of Xenopus ribosomal RNA to the polytene chromosomes of Sciara ocellaris showed that the ribosomal cistrons are localized at the proximal end of the X-chromosome where a large nucleolus is normally formed. Autoradiography of polytene chromosomes from salivary glands incubated for short time in medium containing ³H-uridine, showed a high incorporation in the nucleoli and in active chromosomal bands and a lower labelling over the rest of the chromosomes. In the nucleolus, the silver grains are concentrated in small carrot shaped clamps. These nucleolar subunits have a mean axial length of 2.4 ± 0.5 m m and are arranged in tandem. Each nucleolus has an average of 81 subunits. It is concluded that these subunits correspond to transcribing ribosomal cistrons. In the nuclei of salivary gland cells it is common to find numerous micronucleoli some of which are associated with several sites along the polytene chromosomes. Our data suggest that the micronucleoli are not produced at these chromosome sites, but, rather, represent nucleolar subunits detached from the main nucleolus.

Keywords: Nucleolar subunits; Sciara ocellaris.

REFERENCES

Amabis, J.M. and Nair, K.K. (1976). Ultrastructure of gene transcription in spermatocytes of Trichosia pubescens Morgante, 1969 (Diptera; Sciaridae). Z. Naturforsch. 31c: 186-189.

Birnstiel, M., Speirs, J., Purdon, I., Jones, K. and Loening, U.E. (1968). Properties and composition of the isolated ribosomal DNA satellite of Xenopus laevis. Nature 219: 454-463.

Brown, D.D. and Weber, C.S. (1968). Gene linkage by RNA-DNA hybridization I. Unique DNA sequences homologous to 4S RNA, 5S RNA and ribosomal RNA. J. Mol. Biol. 34: 661-680.

Crouse, H.V., Gerbi, SA, Liang, C.M., Magnus, L. and Mercer, I.M. (1977). Localization of ribosomal DNA within the proximal X heterochromatin of Sciara coprophila (Diptera; Sciaridae). Chromosoma 64: 305-318.

da Cunha, A.B., Pavan, C., Morgante, J.S. and Garrido, M.C. (1969). Studies on cytology and differentiation in Sciaridae. II. DNA redundancy in salivary gland cells of Hybosciara fragilis (Diptera; Sciaridae). Genetics (Suppl.) 61: 335-349.

Derksen, J., Trendelenburg, M.F., Scheer, U. and Franke, W.W. (1973). Spread chromosomal nucleoli of Chironomus salivary glands. Exp. Cell Res. 80: 476-479.

Dessen, E.M.B. and Perondini, A.L.P. (1976). Evidence of hormonal control of the nucleolar activity in Sciara ocellaris. Cell Differentiation 5: 275-282.

Dessen, E.M.B. and Perondini, A.L.P. (1985a). Effects of ecdisterone on nucleolar activity in salivary glands of Sciara ocellaris. Caryologia 38: 309-317.

Dessen, E.M.B. and Perondini, A.L.P. (1985b). RNA ribossômico da glândula salivar de Sciara ocellaris durante o desenvolvimento larval. Cien. Cult. 31: 530-536.

Gabrusewycz-Garcia, N. and Kleinfeld, R.G. (1966). A study of the nucleolar material in Sciara coprophila. J. Cell Biol. 29: 347-359.

Gabrusewycz-Garcia, N. (1972). Further studies of the nucleolar material in salivary gland nuclei of Sciara coprophila. Chromosoma 38: 237-254.

Gerbi, S.A. (1971). Localization and characterization of the ribosomal RNA cistrons in Sciara coprophila. J. Mol. Biol. 58: 499-511.

Gerbi, SA. and Crouse, H.V. (1976). Further studies on the ribosomal cistrons of Sciara coprophila (Diptera). Genetics 83: 81-90.

Hameister, H. (1977). RNA synthesis in isolated polytene nuclei from Chironomus tentans. Chromosoma 62: 217-242.

Hennig, W. and Meer, B. (1971). Reduced polyteny of ribosomal RNA cistrons of Drosophila hydei. Nat. New Biol. 233: 70-72.

Horobin, RW. and Murgatroyd, L.B. (1969). The identification and purification of pyronin and rhodamine dyes. Stain Tech. 44: 297-302.

Kurnick, N.B. (1955). Pyronin Y in the methyl green-pyronin histological stain. Stain Tech. 30: 213-230. Meyer, G.F. and Hennig, W. (1974). The nucleolus of primary spermatocytes of Drosophila hydei. Chromosoma 46: 121-144.

Miller, O.L. and Beatty, B.R. (1969). Visualization of nucleolar genes. Science 164: 955-957.

Pardue, M.L., Gerbi, S.A., Eckhardt, R.A. and Gall, J.G. (1970). Cytological localization of the DNA complementary to ribosomal RNA in polytene chromosomes of Diptera. Chromosoma 29: 268-290.

Renkawitz, R., Gerbi, S.A. and Glaetzer, K.H. (1979). Ribosomal DNA of the fly Sciara coprophila has a very small and homogeneous repeat unit. Molec. Gen. Genet. 173: 1-13.

Spear, B.B. (1974). The genes for ribosomal RNA in diploid and polytene chromosomes of Drosophila melanogaster. Chromosoma 48: 159-179.

Spear, B.B. and Gall, J.G. (1973). Independent control of ribosomal gene replication in polytene chromosomes of Drosophila melanogaster. Proc. Natl. Acad. Sci. (USA) 70: 1359-1363.

Stocker, A.J., Fresquez, C. and Lentzios, G. (1978). Banding studies on the polytene chromosomes of Rhynchosciara hollaenderi. Chromosoma 68: 337-356.

Terra, W.R., Bianchi, A.G., Gambarini, A.G., Pueyo, M.T. and Lara, F.J.S. (1976). A medium for short-term incubation of salivary glands based on the haemolymphy composition of the fly R. americana. Cienc. Cult. 28: 654-657.

Trendelenburg, M.F., Spring, H., Scheer, U. and Franke, W.W. (1974). Morphology of nucleolar cistrons in a plant cell, Acetabularia mediterranea. Proc. Natl. Acad. Sci. (USA): 71: 3626-3630.