Balbiani

Aziz, J.B., N.M. Akrawi, and G.A. Nassori. 1991. The effect of chronic toxicity of copper on the activity of Balbiani rings and nucleolar organizing region in the salivary gland chromosomes of Chironomus ninevah larvae. Environ. Pollut. 69 125-130. 

Lamb, M.M. and Daneholt, B. (1979) Characterization of active transcription units in Balbiani rings of Chironomus tentans. Cell. 17(4), 835-848. 

Singh, O.P., Bjorkroth, B., Masich, S., Wieslander, L. and Daneholt, B. (1999) The intranuclear movement of Balbiani ring pre-messenger ribonucleoprotein particle. Exp. Cell Res., 251, 135-146. 

Grossbach, E. R., Bjorkroth, B., and Daneholt, B. (1990). Presence of histone HI on an active Balbiani ring gene. Cell (Cambridge, Mass.) 60, 78-83. 

Trepte, H. H. (1993). Ultrastructural analyrsis of Balbiani ring genes of Chironomus pallidivittatus in different states of Balbiani ring activity. Chromosoma 102, 433-445. 

Visa. N., Izaurralde, E., Ferreira, J.. Daneholt, B., and Mattaj, I. W. (1996). A nuclear cap-binding complex binds Balbiani ring pre-mRNA cotranscriptionally and accompanies the ribonucleoprotein particle during nuclear export. J. Cell Biol. 133(1), 5-14. 

Fig. 9. The RNP granules in the Balbiani rings of the Chironomus salivary gland. A. the region of a Balbiani ring numerous particles are visible B., C. the particles in the region of chromosome one can see the joining strands between the particles and chromatin material D. E. the particles moving across the pores of the nuclear membrane. A, X22,500 B, X49,500 C to E, X90,000. (From Stevens and Swift. 1966. J. Cell Biol., 31 55-77.)...

The first observations in situ of complexes containing D-RNA were made by Beermann and Bahr (1954) (see also Beermann and Clever, 1964), who found by electron microscopy a special type of granule in the nuclei of the salivary glands of Chironomus, These particles are about 400 A in diameter. They are accumulated in the region of Balbiani rings, which are the sites of intensive synthesis of mRNA that presumably serves as templates for the production of salivary proteins (Beermann, 1961). It is important to... 

Some support for this idea may be found in electron microscopic observations. Usually the structures described as D-RNP are observed directly in the area of active RNA synthesis in the chromosomes. Thus the Beermann particles at first appear in Balbiani rings engaged in the production of D-RNA. The perichromatin and interchromatin granules are also sometimes observed in contact with chromosomal masses, with which they are connected by 30A strands. Finally, the helical structures described in Amoeba, which are presumably also D-RNP, grow from a central axis that probably corresponds to a DNP strand. Of course, these observations are indirect, but they are quite compatible with the view that the ribonucleoprotein complex is formed immediately after the synthesis of D-RNA, even before completion of the RNA chain. 

Beermann, W. 1961. Bin Balbiani-ring als locus einer speicheldrusen-mutation. Chromosoma, 12 1-25. 

Furthermore, no differences were found in the electrophoretic spectra of salivary gland proteins in two strains of Chironomus thummi with either two or three Balbiani s rings. In the strain with an additional ring of Balbiani, intensive RNA synthesis was observed (Wobus et al., 1971). 

Both fractions differ in regard to their stability. The former fraction was no longer obtained in the cytoplasm after 1 to 2 days. The latter type of RNA could be obtained in the cells even after several days. It is, apparently, the product of the Balbiani s ring-2 (BR-2) and possibly also BR-1. The RNA may also be organospe-cific since it was obtained only from salivary glands and not from the intestine (Fig. 17 Edstrdm and Tanguay, 1974). The amount of this RNA in the cytoplasm is approximately equal to 2500 pg per cell and it has a half-life of about 20 h in the cytoplasm and 65 min in the nucleus. Almost all of this RNA is transported from the nucleus into the cytoplasm (Edstrom et al., 1978). 

Puff formation starts morphologically with the formation of a pale zone in the chromosome and disappearance of the precise outlines of the transverse strips and discs. The disc outlines then disappear and the chromosome starts to thicken in this area. There is a wide gradation of puffs in size from those in which all that can be seen is a pale zone, through small puffs to very large ones (Balbiani s rings). Large puffs contain masses of products synthesized at that particular locus, namely RNA and protein, and these can easily be detected by specific chromosomal staining methods. Several models have been produced to illustrate the structure of puff formation, and one of them is illustrated in Fig. 55. 

Fig. 55. a-c) Several stages of formation of a puff (Balbiani s ring) at locus BRx in chromosome IV of a salivary gland cell of Chironomus d) interpretation (after Beermann) of mechanism of puff formation during change in length and shape of chromosomal fibrils (Clever, 1964b Beermann, 1952). 

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