Juan Modolell

Patterning of the Drosophila nervous system: the achaete-scute gene complex

The genes of the achaete-scute complex (AS-C) confer on cells the ability to become neural precursors. Their expression is restricted to groups of cells, the proneural clusters, which occupy specific positions within the embryo neural anlagen and the larva imaginal discs. Neuroblasts or sensory organ mother cells are born within these clusters. Thus, the patterns of expression of the AS-C genes help to define the topology of the nervous system.

The drosophila Extramacrochaetae locus, an antagonist of proneural genes that, like these genes, encodes a helix-loop-helix protein

The Drosophila extramacrochaetae (emc) locus participates in sensory organ patterning by antagonizing, in a mechanistically unknown way, the neurogenic activity of the achaete-scute complex (AS-C). Our cloning of emc DNA and molecular mapping of emc mutations have identified a transcription unit as the most likely candidate for the emc function. It encodes a protein that has a dimerizing helix-loop-helix (HLH) motif but lacks a basic region presumably important for DNA binding. AS-C and other proneural proteins have both domains. We propose that the emc product antagonizes neurogenesis by sequestering proneural proteins in complexes inefficient for DNA interaction. These and other findings suggest the existence of a network of synergistic and antagonistic interactions, mediated by HLH proteins, that participates in the establishment of the neural fate.

Molecular genetics of the achaete-scute gene complex of D. melanogaster

The achaete-scute gene complex (AS-C), involved in differentiation of the sensory chaetes of D. melanogaster, and the yellow locus have been cloned. The yellow locus is the most distal and is followed, proximally, by the achaete and the scute loci. In the scute locus (75 kb), three transcription units separated by long stretches of DNA give rise to poly(A)+ RNAs of 1.6, 1.2, and 1.6 kb. Most DNA lesions associated with scute mutations map within the presumably untranscribed DNA. Their mutant phenotypes are stronger the closer the lesions are to the structural gene of one transcript (T4 RNA). Genetic and developmental data suggest that only this RNA is fundamental for the scute function. Its transcription might be perturbed by far removed DNA lesions. A second transcript is probably implicated in the lethal of scute embryonic function, while the third transcript is unnecessary for the differentiation of most macrochaetes. Two additional polyadenylated RNAs are transcribed from the achaete (1.1 kb) and yellow (1.9 kb) loci.

Excess function Hairy-wing mutations caused by gypsy and copia insertions within structural genes of the achaete-scute locus of Drosophila

Hairy-wing (Hw) mutations cause the differentiation of extra chaetes on the cuticle of Drosophila. They are associated with modifications of the achaete-scute complex that consist, in the mutants studied, of insertions of the transposable elements gypsy (Hw1, HwBS) or copia (HwUa). gypsy and copia are inserted in achaete and scute transcribed regions, respectively. Transcription of the insertion-split genes starts at the normal site but terminates within the transposable element sequences. The RNA truncated within gypsy is 5-20 times more abundant than its homolog in wild-type flies. The abundance is reduced in Hw1 revertants and Hw1 stocks carrying su(Hw) mutations. These and other data suggest that the excess function phenotypes of Hw mutations are generated by an increase in achaete or scute transcripts.

Inhibition of ribosomal translocation by aminoglycoside antibiotics

Abstract The translocation of AcPhe-tRNA in a purified system and that of peptidyl-tRNA in a crude, complete polypeptide synthesizing system containing endogenous E. coli polysomes are inhibited by antibiotics of the neomycin, kanamycin and gentamicin groups. The extent of inhibition varies with the different antibiotics, but it correlates well with the capacity of each antibiotic to inhibit polypeptide chain elongation. Thus, the inhibition of translocation by these antibiotics is clearly significant for their inhibitory effect on polypeptide synthesis.

Induction of translational errors (misreading) by tuberactinomycins and capreomycins

Abstract The well characterized translocation inhibitor viomycin (=tuberactinomycin B) promotes translational errors (misreading) in an in vitro system from Escherichia coli. It strongly stimulates both the binding of noncognate Tyr-tRNA to poly(U)-programmed ribosomes and the subsequent synthesis of acPhe(Tyr)n-tRNA ( n ⋍20 ). The closely related antibiotics capreomycin and tuberactinomycins A,N and O also inhibit translocation and induce misreading.

Functional interaction of neomycin B and related antibiotics with 30S and 50S ribosomal subunits.

Abstract Antibiotics of the neomycin, kanamycin and gentamicin, but not streptomycin, groups stabilize the GDP·elongation factor (EF) G·50S subunit·fusidic acid complex. Treatment of 30S subunits, but not of 50S subunits, with neomycin B or kanamycin B, followed by removal of excess unbound antibiotic and supplementation with untreated complementary subunits, promotes poly(U)-dependent binding of Tyr-tRNA to the reassociated ribosomes (misreading). A similar treatment of either ribosomal subunit with neomycin B inhibits the EF-G-dependent translocation of Ac-Phe-tRNA. These results suggest that interaction of neomycin B and related antibiotics with the 30S subunit induces misreading and inhibits translocation, and interaction with the 50S subunit stabilizes EF-G on the ribosome and also inhibits translocation.

One-hundred and five new potential Drosophila melanogaster genes revealed through STS analysis

Complementation analysis had suggested that the Drosophila melanogaster genome contains approximately 5000 genes, but it is now generally accepted that the actual number is several times as high. We report here an analysis of 1788 anonymous sequence tagged sites (STSs) from the European Drosophila Genome Project (EDGP), totalling 463 kb. The data reveal a substantial number of previously undescribed potential genes, amounting to 6.1% of the number of Drosophila genes already in the sequence databases.