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Biomedical subjects

S Kerridge

Publications and source records attributed to S Kerridge.

27 records · Page 2Linked to original sources
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↗
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↗
PubMed1981

Distal into proximal (Dipr): a homoeotic mutation of Drosophila melanogaster.

The morphology and genetical characteristics of a new dominant homoeotic mutation, called Distal into proximal (Dipr), are described. Dipr causes two main abnormalities, both of which are specific to distal regions of the adult appendages (i.e. the wing, haltere, legs, antenna, and proboscis); first that distal parts are reduced in size and second that the patterns found distally resemble those normally localised in more proximal parts. The mutation maps to the right arm of chromosome 3 and is associated with an inversion with breakpoints in 84D and 84F. Analysis of revertants of Dipr show that the right breakpoint of In(3R)Dipr is the one responsible for the mutant phenotype. Complementation analyses of Dipr revertants and dosage studies of Dipr with different doses of Dipr+ indicate that the mutant is a hypermorph affecting the normal expression of a gene localised in 84F. The developmental significance of the mutation is discussed.

Animals↗
PubMed1981

Developmental analysis of the homoeotic mutation bithoraxoid of Drosophila melanogaster.

The homoeotic transformations caused by bxd are described in detail. The anterior histoblast nests of the first abdominal segment are missing, and are replaced by one or two leg discs ventrally. Mainly anterior compartment patterns are found in the ectopic, abdominal legs of adult flies. However, cell lineage analyses show that both anterior and posterior polyclones are established early in the development of these ectopic legs, but the posterior polyclone is smaller. Cells of the anterior polyclone may regulate later in development to adjust for this and form pattern elements normally derived from the posterior polyclone. In addition, experiments show that bxd+ is required by the second larval instar stage, and possibly as early as the blastoderm stage.

Animals↗
PubMedDate not supplied

Trunk-specific modulation of wingless signalling in Drosophila by teashirt binding to armadillo.

BACKGROUND: One function of the Wingless signal cascade is to determine the 'naked' cuticle cell-fate choice instead of the denticled one in Drosophila larvae. Wingless stabilises cytoplasmic Armadillo, which may act in a transcriptional activator complex with the DNA-binding protein T-cell factor (also known as Pangolin). As these components are critical for all Wingless-dependent patterning events, the problem arises as to how specific outputs are achieved. RESULTS: The Teashirt zinc finger protein was found to be necessary for a subset of late Wingless-dependent functions in the embryonic trunk segments where the teashirt gene is expressed. Teashirt was found to be required for the maintenance of the late Wingless signalling target gene wingless but not for an earlier one, engrailed. Armadillo and Teashirt proteins showed similar Wingless-dependent modulation patterns in homologous parts of each trunk segment in embryos, with high levels of nuclear Teashirt and intracellular Armadillo within cells destined to form naked cuticle. We found that Teashirt associates with, and requires, Armadillo in a complex for its function. CONCLUSIONS: Teashirt binds to, and requires, Armadillo for the naked cell-fate choice in the larval trunk. Teashirt is required for trunk segment identity, suggesting that Teashirt provides a region-specific output to Armadillo activity. Further modulation of Wingless is achieved in homologous parts of each trunk segment where Wingless and Teashirt are especially active. Our results provide a novel, cell-intrinsic mechanism to explain the modulation of the activity of the Wingless signalling pathway.

Animals↗