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Biomedical subjects

G Morata

Publications and source records attributed to G Morata.

At least 55 records · Page 3Linked to original sources
PubMed1989

Structure and function of the bithorax complex genes of Drosophila.

The bithorax complex consists of three genes, Ubx, abd-A and Abd-B, which together specify the characteristic development of parasegments 5 to 13 of Drosophila. These genes are structurally homologous; they are of similar size, are transcribed in the same orientation and they all have a homeobox near the 3' end of their transcription unit. Genetic and molecular analyses of Ubx suggest that the gene contains one transcription unit encoding the protein products and at least three cis-regulatory regions. Two of these, abx and bxd, promote the activity of the Ubx transcription unit to the levels appropriate for parasegments 5 and 6, respectively. A third regulatory element, called Cbx-like, prevents the expression of Ubx anterior to parasegment 5. The gene abd-A is not as well known, but genetic and molecular studies indicate at least one cis-regulatory region downstream of the 3' end of the transcription unit. In the gene Abd-B there are two distinct trans-acting elements, called m and r. The m element is a conventional homeotic function, which specifies the identity of parasegments 10 to 13. The r element is specific for parasegment 14 where it suppresses a number of homeotic functions (including m). Molecular analysis indicates that Abd-B contains two transcription units with a common 3' end which correspond to the m and r elements defined genetically.

Animals↗
PubMed1989

Genetic structure of the abd-A gene of Drosophila.

We report the embryonic and adult phenotypes of a number of mutations of the abd-A gene of the bithorax complex. Some of them result in loss of abd-A function in the whole abd-A domain and are usually lethal. These probably eliminate or inactivate abd-A protein products. Other mutations affect only part of the abd-A domain. These are viable, appear to map outside the abd-A transcription unit, and presumably alter the normal spatial regulation of abd-A products. We propose a model of abd-A structure based on a protein-coding region and two cis-regulatory regions. Regulatory region 1, 3' to the transcription unit, contains positive and negative regulatory elements. Regulatory region 2, 5' to the transcription unit, establishes the correct level of abd-A activity in the abdominal metameres.

Animals↗
PubMed1988

Developmental analysis of a hybrid gene composed of parts of the Ubx and abd-A genes of Drosophila.

C1 is a mutation in the bithorax complex (BX-C) of Drosophila resulting from the deletion of parts of the Ubx and abd-A genes. We show that the ;hybrid' gene formed by the fusion of the remaining parts of Ubx and abd-A (5'abd-A/Ubx3') is functional and developmentally active. It specifies parasegment patterns with a mixture of thoracic and abdominal identities. The hybrid gene also has other properties typical of conventional bithorax genes: it can be spatially derepressed in the absence of trans-acting genes like extra Sex combs or Polycomb and in turn represses other homeotics like Sex combs reduced. The comparison of embryos containing exclusively hybrid gene activity with others having no BX-C function indicates that the hybrid gene is active in the body region defined by PS5 to PS14. The expression in PS5 and PS6 suggests that one control region (abx) of Ubx can regulate the transcription of the abd-A promoter.

Journal Article↗
PubMed1988

Ectopic expression of homeotic genes caused by the elimination of the Polycomb gene in Drosophila imaginal epidermis.

The morphological patterns in the adult cuticle of Drosophila are determined principally by the homeotic genes of the bithorax and Antennapedia complexes. We find that many of these genes become indiscriminately active in the adult epidermis when the Pc gene is eliminated. By using the Pc3 mutation and various BX-C mutant combinations, we have generated clones of imaginal cells possessing different combinations of active homeotic genes. We find that, in the absence of BX-C genes, Pc- clones develop prothoracic patterns; this is probably due to the activity of Sex combs reduced which overrules Antennapedia. Adding contributions of Ultrabithorax, abdominal-A and Abdominal-B results in thoracic or abdominal patterns. We have established a hierarchical order among these genes: Antp less than Scr less than Ubx less than abd-A less than Abd-B. In addition, we show that the engrailed gene is ectopically active in Pc- imaginal cells.

Animals↗
PubMed1987

Double and triple mutant combinations of bithorax complex of Drosophila.

We have constructed double and triple mutant combinations for the Ubx, abd-A and Abd-B genes of the bithorax complex and have examined the homeotic transformations they produce in the larval and adult patterns. Embryos hemizygous for the triple combination exhibit a metameric pattern consisting of parasegments 5-12 being transformed into parasegment 4. In addition, parasegment 13 develops like a mixture of parasegment 3 and 4, and parasegment 14 is abnormal. The same phenotype is displayed by embryos homozygous for DfP9, lacking all the BX-C DNA, >300 kb. This result strongly supports the notion that the BX-C contains only three genes which account for all the developmental functions of the complex. The phenotypes of the different double combinations also support the same view; the Ubx abd-a comthoracic and several abdominal functions. The abd-A Abd-B combination exhibits the same phenotype of DpP10 DfP9, lacking all the abdominal functions except those specific for A1. Our results also indicate that each BX-C gene becomes active autonomously regardless of the presence or functional state of the other BX-C genes.

Animals↗
PubMed1986

Identification and characterization of a parasegment specific regulatory element of the abdominal-B gene of Drosophila.

We have characterized mutations of the Abdominal-B gene of the bithorax complex of Drosophila. We conclude that the gene contains two distinct genetic elements: one has a morphogenetic role and acts in parasegments 10, 11, 12, and 13, while the other acts on parasegment 14 and has primarily or exclusively a regulatory function. Evidence indicates that the latter suppresses the activity of the morphogenetic element of Abd-B and of other genes responsible for the development of sclerotic plates. The regulatory element also suppresses those BX-C genes and other homeotics that, in the absence of Polycomb or extra sex combs function, can become active in parasegment 14.

Abdomen↗
PubMed1985

Prothoracic transformation and functional structure of the Ultrabithorax gene of Drosophila.

The activity of the Ultrabithorax (Ubx+) gene is necessary for the characteristic development of a particular anatomical domain of the body of Drosophila. Mutant alleles at the abx, bx, bxd, and pbx loci eliminate specific functions of Ubx+ since their phenotype is part of that of Ubx mutants. We have characterized several abx and bx alleles and found that their effect extends to the same anatomical subdomain. This suggests that they inactivate the same genetic subunit within Ultrabithorax. Also, their wild-type activity is required for two distinct functions: postprothorax, acting early in the embryonic period, and bithorax, acting through embryonic and larval periods. Our results suggest that the Ultrabithorax gene contains two genetic subunits and that each subunit may include two separate functions.

Alleles↗
PubMed1985

Contrabithorax and the control of spatial expression of the bithorax complex genes of Drosophila.

Cbx1 is a dominant mutation of the bithorax complex (BX-C) of Drosophila partially transforming the second thoracic (T2) segment towards the third one (T3). Molecular analysis has shown that Cbx1 arose from a transposition within the BX-C of a DNA fragment of 17 kb containing pbx+ inserted into the Ubx area. In addition to the dominant phenotype, the Cbx1 mutation produces a set of recessive homeotic transformations that we show are characteristic of the Ubx mutations. We present evidence that the dominant and the recessive transformations arise from different mechanisms and suggest the dominant transformation is caused by an alteration of the normal regulatory role of pbx+ resulting in an adventitious expression of some Ubx+ products in T2, while the Ubx phenotype is caused by the breakpoint of the insertion.

Animals↗
PubMed1983

The phenotype of engrailed mutations in the antenna of Drosophila.

The eye-antenna imaginal disc of Drosophila is subdivided into anterior and posterior compartments and it is expected therefore that the engrailed gene would be locally required in the posterior compartment. Here we describe the phenotype of engrailed mutations in the antenna. Clones of cells which were mutant for en1/enC2 were produced in wild-type antennae by mitotic recombination. The clones showed the typical syndrome of cells mutant for engrailed, being normal in the anterior compartment and showing partial posterior-to-anterior transformation in the posterior compartment.

Animals↗
PubMed1983

Homeotic transformations of the abdominal segments of Drosophila caused by breaking or deleting a central portion of the bithorax complex.

In Drosophila, genes in the centromere-proximal portion of the bithorax complex (BX-C) have been shown to control the development of the metathorax, and parts of the mesothorax and first abdominal segment. Here, we explore the roles of genes positioned more distally by examining the larval and adult phenotypes caused by a breakpoint and deletion in the middle of the complex. We find that both aberrations affect only abdominal segments, transforming the more anterior segments towards the first abdominal segment, and the remaining segments into a graded series of novel segment types which are partially transformed towards more anterior abdominal segments. Moreover, the adult transformations, which we have observed in somatic clones of mutant cells, are in close accord with the transformations observed in mutant first instar larvae, and appear to be expressed in a cell autonomous fashion. We discuss these results in the light of current views of the organization and function of the complex.

Abdomen↗
PubMed1983

Genetic and developmental characteristics of the homeotic mutation bx1 of Drosophila.

The mutations at the bithorax locus produce a transformation of anterior haltere into anterior wing. The bx1 allele presents unusual features when compared with other bx alleles. The phenotype of bx1 homozygotes is temperature sensitive but only with regard to the distal and not to the proximal transformation, thus suggesting two different components in the bithorax transformation. The phenotype of bx1 homozygotes is stronger than that of bx1 over the deletion of the gene, suggesting a trans interaction of the bx1 chromosomes which results in mutual partial inactivation. We show by temperature shift and clonal analysis experiments that the decision on whether to differentiate haltere or wing structures is taken at the end of the proliferation period of the mutant disc.

Alleles↗
PubMed1982

The role of position in determining homoeotic gene function in Drosophila.

Homoeotic mutations of Drosophila lead to the replacement of one structure by another, for example, Antennapedia replaces the antenna with a mesothoracic leg and bithorax produces an anterior wing instead of the anterior haltere. The transformed structures differentiated by the homoeotic mutants are essentially normal--only the position in which they appear is abnormal. The mutant phenotypes suggest that in normal development homoeotic genes are involved in developmental alternatives and contribute to a genetic address that defines the particular developmental pathway taken by a primordial group of cells. Thus, in the absence of homoeotic gene function, primordia in different positions should follow the same basic developmental pathway. This is indeed the case for embryos that show no activity of bithorax genes; thoracic and abdominal segments develop as mesothorax. The simplest view on homoeotic gene function is that the genes act selectively on primordia depending on their position in the embryo. To test this hypothesis, we used a mutation at the Antennapedia locus, Antp, which transforms the antenna into a mesothoracic leg, and we observed the function of the homoeotic genes engrailed and Ultrabithorax in two apparently morphologically identical appendages which develop from primordia in different positions. Our results indicate that position is the relevant factor in the function of these two homoeotic genes.

Animals↗
PubMed1981

Sequential functions of the bithorax complex of Drosophila.

The bithorax genes are a group of homoeotic genes of Drosophila whose function is related to the control of segment development. They form a gene complex in which at least seven different loci have been identified. Mutations at each of these loci produce a specific homoeotic transformation whereby a segment is transformed either in part or completely into another. In embryos completely deficient for the bithorax genes, all the thoracic and abdominal segments resemble mesothoracic segments. This observation, together with the segmental specificity of the mutant phenotypes, led Lewis to suggest a model of genetic control in which the type of development in each segment is specified by the activation of a fraction of the total number of bithorax genes. Thus, lack of activity of the bithorax genes results in mesothoracic development, activation of the bithorax (bx+) and postbithorax (pbx+) genes produces metathorax (anterior and posterior respectively), and activation of these two genes with bithoraxoid (bxd+) produces the first abdominal segment and so on. Although this model explains the genetic and developmental data, it leaves unexplained formation of the prothoracic segment. We now describe two unexpected results: deficiencies for bithorax genes can lead to segments being transformed into prothorax, and there is a temporal sequence in the function of the bithorax system.

Animals↗