Family of developmentally regulated, maternally expressed Drosophila RNA species detected by a v-myc probe

Myc/Max/Mad in invertebrates: the evolution of the Max network

The Myc proto-oncogenes, their binding partner Max and their antagonists from the Mad family of transcriptional repressors have been extensively analysed in vertebrates. However, members of this network are found in all animals examined so far. Several recent studies have addressed the physiological function of these proteins in invertebrate model organisms, in particular Drosophila melanogaster. This review describes the structure of invertebrate Myc/Max/Mad genes and it discusses their regulation and physiological functions, with special emphasis on their essential role in the control of cellular growth and proliferation.

Functions of maternal mRNA in early development

In this review, the types of mRNAs found in oocytes and eggs of several animal species, particularly Drosophila, marine invertebrates, frogs, and mice, are described. The roles that proteins derived from these mRNAs play in early development are discussed, and connections between maternally inherited information and embryonic pattern are sought. Comparisons between genetically identified maternally expressed genes in Drosophila and maternal mRNAs biochemically characterized in other species are made when possible. Regulation of the meiotic and early embryonic cell cycles is reviewed, and translational control of maternal mRNA following maturation and/or fertilization is discussed with regard to specific mRNAs.

Search for Drosophila genes encoding a conserved domain present in the achaete-scute complex and myc proteins

Several genes of the achaete-scute complex (AS-C) of Drosophila melanogaster encode a 60 amino acids long conserved domain which shares a significant homology with a region of the vertebrate myc proteins. Based on these results, the existence of a family of Drosophila genes that would share both this conserved domain and the neurogenic function of the AS-C has been postulated. To test this proposal, we have searched a D. melanogaster genomic library with a probe that encodes the conserved domain. Only under very low stringency hybridization conditions, clones not belonging to the AS-C cross-hybridized with the probe. Those that gave the strongest signals were characterized. Sequencing of the cross-hybridizing regions showed that they had no significant homology with the conserved domain, the sequence similarity extending at the most for 37 nucleotides. Although our results do not conclusively disprove the existence of a family of AS-C-like genes, they indicate that the conservation of the domain would be lower than that found for shared motifs in other families of Drosophila developmental genes.

Nucleotide sequence of the first exon of the rat c-myc gene: proviral insertions in murine leukemia virus-induced lymphomas do not affect exon 1

We have previously reported that proviruses are integrated adjacent to the c-myc gene in rat thymomas induced by murine leukemia viruses. In order to characterize these insertions, we have isolated recombinant DNA clones from normal rat DNA containing all of the normal rat c-myc gene, and from two Moloney murine leukemia virus-induced lymphomas containing both proviral and adjacent rat c-myc sequences. We determined the DNA sequence of portions of the normal and one tumor-derived clone. The normal and tumor-derived exon 1 sequences are identical. By comparing our sequence to the sequences of mouse and human c-myc, we located the first exon of the rat c-myc gene. Analysis of the tumor-derived rat c-myc clones showed that proviral integration occurred approximately 1.4 kb upstream of exon 1 of c-myc in the case of one tumor and 0.55 kb upstream of c-myc exon 1 in the other. Thus, we conclude that the proviral insertions in these tumors did not affect the rat c-myc gene by altering the structure of the c-myc RNA. Consistent with this, the c-myc RNA present in a cell line derived from one of these tumors is identical in size to the normal c-myc RNA. Furthermore, the level of c-myc expression is not dramatically elevated in this cell line. Exon 1 of the rat c-myc gene contains no ATG start codons and contains multiple stop codons in all three reading frames, indicating that it, like the chicken and mouse exon 1 sequences, is noncoding. The extent of homology between our sequence of rat c-myc exon 1 and the published sequence of human c-myc exon 1 is similar to the extent of homology between the sequences of mouse and human c-myc exon 1. The rat and mouse c-myc exon 1 sequences differ from each other by about the amount predicted from the known divergence times of mice from rats. Exon 1 of c-myc is only slightly conserved, evolving at a rate similar to that seen for introns and pseudogenes.

Similarities between a conserved sequence element of homoeo boxes and other genes

We report here the homology of different genes with an 18-nucleotide sequence element derived from a conserved region of the homoeo boxes. Possible evolutionary relationships are discussed.

A Drosophila genomic sequence with homology to human epidermal growth factor receptor

Vertebrate genomes contain an extensive family of genes possessing varying degrees of homology to the v-src oncogene. Most src-related proteins identified to date are intracellular and membrane-associated, although some are transmembrane proteins and function as receptors for peptide growth factors. Three Drosophila gene sequences related to the v-src gene have been identified, each exhibiting a high degree of homology to one or more of the src-family members encoding an intracellular protein. We have isolated a panel of cloned Drosophila sequences exhibiting weak v-src hybridization and were interested to determine whether any members of this group represented homologues of additional known src-family genes, especially those functioning as growth factor receptors. As we report here, four of these clones, representing overlapping portions of the same genomic segment, hybridized preferentially with the v-erb-B oncogene and were further characterized. The deduced amino-acid sequence from a portion of this Drosophila genomic segment is 77% homologous to the kinase domain of human epidermal growth factor (EGF) receptor, a substantially greater degree of homology than was observed with any other known src-family member. By hybridization with a human EGF receptor complementary DNA clone probe, we demonstrate that the same genomic segment showing homology with the kinase domain also contains sequences related to the extracellular domain of the EGF receptor gene.