Tissue localization of Drosophila melanogaster ras transcripts during development.

Abstract

Three ras homologs have been identified in Drosophila melanogaster. Here we describe the tissue distribution of their transcripts as analyzed by in situ hybridization. The RNAs of the three genes show a similar distribution at every developmental stage examined. In embryos, the transcripts are uniformly distributed. In larvae, ras transcripts are restricted to dividing cells (e.g., imaginal disks, gonads, and brain). At the adult stage, several tissues contain ras transcripts. The strongest hybridization signals are localized to the adult ovaries and to the cortex of the brain and ganglia, which at this stage are comprised of differentiated, nondividing cells. The tissue distribution of ras transcripts in D. melanogaster suggests that the ras proteins have multiple roles during development which may be related to both the proliferative and differentiated states of the tissues.The vertebrate p21 ras proteins are membrane-associated proteins (33) which have GTP-binding activity (18). They were shown to be involved in a variety of viral (5) and non-virus-associated tumors. In human and rodent tumors, ras genes were shown to be activated by a point mutation in codon 12 (21, 27) or codon 61 (29,36). The GTP-binding activity and the structural homology to other GTP-binding proteins such as transducin (28) have suggested that p21 ras may play a role as a transducer of mitogenic signals from the plasma membrane into the cell. Indeed, it appears that mutations which lead to oncogenic activation of ras exert their effect by reducing an intrinsic GTPase activity of ras (14,26), similar to the effect of various bacterial toxins or GTP analogs on G proteins (8). Under these conditions, the G proteins transmit the signal continuously without being triggered by the appropriate receptor.ras genes were found to be highly conserved in evolution and so far are the only oncogenes shown to be conserved not only in Drosophila melanogaster (16, 23) but also in yeasts (6,20) and slime molds (22). In yeasts, the ras proteins appear to regulate the adenylate cyclase pathway (31), whereas in vertebrates, they probably participate in a different pathway (3). In addition to the high degree of structural conservation, another feature of ras which has been conserved from yeasts to humans is the multigene nature of this family. There are two genes in bakers' yeast (Saccharomyces cerevisiae) which show a high degree of homology to ras (20) and three ras genes in D. melanogaster (16) as well as in vertebrates (5,29).The most conserved domain of ras within each species and between species is the N terminus, which is also responsible for the GTP-binding activity (9, 30). A variety of structural manipulations of ras genes have shown that this domain is responsible for interaction with the next component in the presumptive signal transduction pathway (4,12,23,35

Differential expression during embryogenesis of three genes clustered in the Ras1 region of Drosophila melanogaster

“…Previous studies utilizing in situ hybridization to tissue sections, revealed a uniform, homogeneous pattern of Rasl transcript distribution in the embryo (Segal and Shilo, 1986). Our results suggest that the distribution of the Rasl transcripts in the embryo is spatially restricted to the CNS (Fig.…”

“…Nevertheless, probes 2 and 5 detected an additional 1.4 kb transcript in the intergenic region between Rasl and the gene encoding the 0.7 kb transcript. Apparently, this novel 1.4 kb transcript is different from the Rasl 1.4 kb transcript detected by Rasl cDNA probes (Lev et al, 1985;Segal and Shilo, 1986) (Fig. lB, lane l l ) , since probe 8, a n asymmetric RNA probe, revealed that it is transcribed in the opposite polarity to Rasl (Fig.…”

P-element-mediated enhancer detection: a versatile method to study development in Drosophila.

“…hi third-instar larvae, the transcripts of Diasl are localized to the brain, imaginal discs, and gonads (Segal and Shilo 1986). The same tissue distribution of p-galactosidase activity is observed in third-instar larvae of transposant A140.1F3 (Gibson and Gehring 1990).…”

“…Embryos of transposant A140.1F3 (85D/E) show p-galactosidase expression in all tissues (data not shown), an expression pattern that corresponds to the embryonic transcript distribution of Diasl (85D), a gene that shares homology with the vertebrate Ha-ras oncogene (Neuman-Silberberg et al 1984;Segal and Shilo 1986). hi third-instar larvae, the transcripts of Diasl are localized to the brain, imaginal discs, and gonads (Segal and Shilo 1986).…”

Conserved cis-elements bind a protein complex that regulates Drosophila ras2/rop bidirectional expression

“…Studies of the spatial distribution of the mRNA transcribed from the two genes during development produced almost identical patterns. Both genes are transcribed -in oocytes, while in early embryos mRNA distribution is localised mostly in the peripheral nervous system (Lev et al, 1985;Segal & Shilo, 1986;Salzberg et al, 1993). Analysis of the rop product revealed a 68 kDa non-nuclear protein situated in both the membranous and the cytosolic subfractions (Salzberg et al, 1993).…”