The Iroquois homeodomain proteins are required to specify body wall identity in Drosophila.
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The Iroquois complex (Iro-C) homeodomain proteins allow cells at the proximal part of the Drosophila imaginal wing disc to form mesothoracic body wall (notum). Cells lacking these proteins form wing hinge structures instead (tegula and axillary sclerites). Moreover, the mutant cells impose on neighboring wild-type cells more distal developmental fates, like lateral notum or wing hinge. These findings support a tergal phylogenetic origin for the most proximal part of the wing and provide evidence for a novel pattern organizing center at the border between the apposed notum (Iro-C-expressing) and hinge (Iro-C-nonexpressing) cells. This border is not a cell lineage restriction boundary. (+info)
ANTHOCYANINLESS2, a homeobox gene affecting anthocyanin distribution and root development in Arabidopsis.
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The ANTHOCYANINLESS2 (ANL2) gene was isolated from Arabidopsis by using the maize Enhancer-Inhibitor transposon tagging system. Sequencing of the ANL2 gene showed that it encodes a homeodomain protein belonging to the HD-GLABRA2 group. As we report here, this homeobox gene is involved in the accumulation of anthocyanin and in root development. Histological observations of the anl2 mutant revealed that the accumulation of anthocyanin was greatly suppressed in subepidermal cells but only slightly reduced in epidermal cells. Furthermore, the primary roots of the anl2 mutant showed an aberrant cellular organization. We discuss a possible role of ANL2 in the accumulation of anthocyanin and cellular organization of the primary root. (+info)
Gnarley1 is a dominant mutation in the knox4 homeobox gene affecting cell shape and identity.
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Maize leaves have a stereotypical pattern of cell types organized into discrete domains. These domains are altered by mutations in knotted1 (kn1) and knox (for kn1-like homeobox) genes. Gnarley (Gn1) is a dominant maize mutant that exhibits many of the phenotypic characteristics of the kn1 family of mutants. Gn1 is unique because it changes parameters of cell growth in the basal-most region of the leaf, the sheath, resulting in dramatically altered sheath morphology. The strongly expressive allele Gn1-R also gives rise to a floral phenotype in which ectopic carpels form. Introgression studies showed that the severity of the Gn1-conferred phenotype is strongly influenced by genetic background. Gn1 maps to knox4, and knox4 is ectopically expressed in plants with the Gn1-conferred phenotype. Immunolocalization experiments showed that the KNOX protein accumulates at the base of Gn1 leaves in a pattern that is spatially and temporally correlated with appearance of the mutant phenotype. We further demonstrate that Gn1 is knox4 by correlating loss of the mutant phenotype with insertion of a Mutator transposon into knox4. (+info)
PLENA and FARINELLI: redundancy and regulatory interactions between two Antirrhinum MADS-box factors controlling flower development.
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We report the discovery of an Antirrhinum MADS-box gene, FARINELLI (FAR), and the isolation of far mutants by a reverse genetic screen. Despite striking similarities between FAR and the class C MADS-box gene PLENA (PLE), the phenotypes of their respective mutants are dramatically different. Unlike ple mutants, which show homeotic conversion of reproductive organs to perianth organs and a loss of floral determinacy, far mutants have normal flowers which are partially male-sterile. Expression studies of PLE and FAR, in wild-type and mutant backgrounds, show complex interactions between the two genes. Double mutant analysis reveals an unexpected, redundant negative control over the B-function MADS-box genes. This feature of the two Antirrhinum C-function-like genes is markedly different from the control of the inner boundary of the B-function expression domain in Arabidopsis, and we propose and discuss a model to account for these differences. The difference in phenotypes of mutants in two highly related genes illustrates the importance of the position within the regulatory network in determining gene function. (+info)
Structural organization and sequence of the homeotic gene Antennapedia of Drosophila melanogaster.
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The structure of the Drosophila melanogaster Antennapedia (Antp) gene has been investigated by the isolation and sequencing of different cDNAs and genomic clones. Northern analysis, S1 mapping and primer extension experiments reveal a complex and unusual gene structure. The gene is composed of two promoters, eight exons spanning >100 kb, and two termination processing regions. Four major polyadenylated transcripts were found, two of them starting at a second internal promoter in front of exon 3. All four transcripts have extremely long untranslated leader and trailer sequences in the range of 1-2 kb. Despite the complex transcriptional organization, the open reading frame is the same in all transcripts, and starts in exon 5 giving rise to a protein of mol. wt. 42 800. The putative protein is rich in glutamine (18%) and proline (10%). The homeobox, a region which previously has been shown to be highly conserved among homeotic genes, is contained in the open reading frame and located in the last exon. Functional implications of the complex structure with respect to development and its relation to the mutant phenotypes are discussed. (+info)
MIG-13 positions migrating cells along the anteroposterior body axis of C. elegans.
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The C. elegans Q neuroblasts and their descendants migrate along the anteroposterior (A/P) body axis to positions that are not associated with any obvious landmarks. We find that a novel protein, MIG-13, is required to position these cells correctly. MIG-13 is a transmembrane protein whose expression is restricted to the anterior and central body regions by Hox gene activity. MIG-13 functions non-cell autonomously within these regions to promote migration toward the anterior: loss of mig-13 activity shifts the Q descendants toward the posterior, whereas increasing the level of MIG-13 shifts them anteriorly in a dose-dependent manner. Our findings suggest that MIG-13 is a component of a global A/P migration system, and that the level of MIG-13 determines where along the body axis these migrating cells stop. (+info)
Activation of a floral homeotic gene in Arabidopsis.
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The patterned expression of floral homeotic genes in Arabidopsis depends on the earlier action of meristem-identity genes such as LEAFY, which encodes a transcription factor that determines whether a meristem will generate flowers instead of leaves and shoots. The LEAFY protein, which is expressed throughout the flower, participates in the activation of homeotic genes, which are expressed in specific regions of the flower. Analysis of a LEAFY-responsive enhancer in the homeotic gene AGAMOUS indicates that direct interaction of LEAFY with this enhancer is required for its activity in plants. Thus, LEAFY is a direct upstream regulator of floral homeotic genes. (+info)
Alternative olfactory neuron fates are specified by the LIM homeobox gene lim-4.
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The Caenorhabditis elegans AWA, AWB, and AWC olfactory neurons are each required for the recognition of a specific subset of volatile odorants. lim-4 mutants express an AWC reporter gene inappropriately in the AWB olfactory neurons and fail to express an AWB reporter gene. The AWB cells are morphologically transformed toward an AWC fate in lim-4 mutants, adopting cilia and axon morphologies characteristic of AWC. AWB function is also transformed in these mutants: Rather than mediating the repulsive behavioral responses appropriate for AWB, the AWB neurons mediate attractive responses, like AWC. LIM-4 is a predicted LIM homeobox gene that is expressed in AWB and a few other head neurons. Ectopic expression of LIM-4 in the AWC neuron pair is sufficient to force those cells to adopt an AWB fate. The AWA nuclear hormone receptor ODR-7 described previously also represses AWC genes, as well as inducing AWA genes. We propose that the LIM-4 and ODR-7 transcription factors function to diversify C. elegans olfactory neuron identities, driving them from an AWC-like state into alternative fates. (+info)