Selector Genes and Limb Identity in Arthropods and Vertebrates

Abstract The gene proboscipedia (pb) is a member of the Antennapedia complex in Drosophila and is required for the proper specification of the adult mouthparts. In the embryo, pb expression serves no known function despite having an accumulation pattern in the mouthpart anlagen that is conserved across several insect orders. We have identified several of the genes necessary to generate this embryonic pattern of expression. These genes can be roughly split into three categories based on their time of action during development. First, prior to the expression of pb, the gap genes are required to specify the domains where pb may be expressed. Second, the initial expression pattern of pb is controlled by the combined action of the genes Deformed (Dfd), Sex combs reduced (Scr), cap'n'collar (cnc), and teashirt (tsh). Lastly, maintenance of this expression pattern later in development is dependent on the action of a subset of the Polycomb group genes. These interactions are mediated in part through a 500-bp regulatory element in the second intron of pb. We further show that Dfd protein binds in vitro to sequences found in this fragment. This is the first clear demonstration of autonomous positive cross-regulation of one Hox gene by another in Drosophila melanogaster and the binding of Dfd to a cis-acting regulatory element indicates that this control might be direct.

Download Full-text

Sequence of the Tribolium castaneum Homeotic Complex: The Region Corresponding to the Drosophila melanogaster Antennapedia Complex

Genetics ◽

10.1093/genetics/160.3.1067 ◽

2002 ◽

Vol 160 (3) ◽

pp. 1067-1074

Author(s):

Susan J Brown ◽

John P Fellers ◽

Teresa D Shippy ◽

Elizabeth A Richardson ◽

Mark Maxwell ◽

...

Keyword(s):

Tribolium Castaneum ◽

Hox Genes ◽

Transcription Unit ◽

Sex Combs Reduced ◽

Sex Combs ◽

Selector Genes ◽

Homeotic Selector Genes ◽

Encoding Genes ◽

Single Cluster ◽

Homeotic Selector

Abstract The homeotic selector genes of the red flour beetle, Tribolium castaneum, are located in a single cluster. We have sequenced the region containing the homeotic selector genes required for proper development of the head and anterior thorax, which is the counterpart of the ANTC in Drosophila. This 280-kb interval contains eight homeodomain-encoding genes, including single orthologs of the Drosophila genes labial, proboscipedia, Deformed, Sex combs reduced, fushi tarazu, and Antennapedia, as well as two orthologs of zerknüllt. These genes are all oriented in the same direction, as are the Hox genes of amphioxus, mice, and humans. Although each transcription unit is similar to its Drosophila counterpart in size, the Tribolium genes contain fewer introns (with the exception of the two zerknüllt genes), produce shorter mRNAs, and encode smaller proteins. Unlike the ANTC, this region of the Tribolium HOMC contains no additional genes.

Download Full-text

Smoothened-mediated Hedgehog signalling is required for the maintenance of the anterior-posterior lineage restriction in the developing wing of Drosophila

Development ◽

10.1242/dev.124.20.4053 ◽

1997 ◽

Vol 124 (20) ◽

pp. 4053-4063 ◽

Cited By ~ 25

Author(s):

S.S. Blair ◽

A. Ralston

Keyword(s):

Gene Expression ◽

Cellular Mechanisms ◽

Hedgehog Signalling ◽

Compartment Boundary ◽

Complex Process ◽

Normal Site ◽

Selector Genes ◽

Signalling Models ◽

To Receive ◽

Anterior Posterior

It is thought that the posterior expression of the ‘selector’ genes engrailed and invected control the subdivision of the growing wing imaginal disc of Drosophila into anterior and posterior lineage compartments. At present, the cellular mechanisms by which separate lineage compartments are maintained are not known. Most models have assumed that the presence or absence of selector gene expression autonomously drives the expression of compartment-specific adhesion or recognition molecules that inhibit intermixing between compartments. However, our present understanding of Hedgehog signalling from posterior to anterior cells raises some interesting alternative models based on a cell's response to signalling. We show here that anterior cells that lack smoothened, and thus the ability to receive the Hedgehog signal, no longer obey a lineage restriction in the normal position of the anterior-posterior boundary. Rather these clones extend into anatomically posterior territory, without any changes in engrailed/invected gene expression. We have also examined clones lacking both en and inv; these too show complex behaviors near the normal site of the compartment boundary, and do not always cross entirely into anatomically anterior territory. Our results suggest that compartmentalization is a complex process involving intercompartmental signalling; models based on changes in affinity or growth will be discussed.

Download Full-text

Needs and Targets for the multi sex combs Gene Product in Drosophila melanogaster

Genetics ◽

10.1093/genetics/149.4.1823 ◽

1998 ◽

Vol 149 (4) ◽

pp. 1823-1838 ◽

Cited By ~ 1

Author(s):

Olivier Saget ◽

Françoise Forquignon ◽

Pedro Santamaria ◽

Neel B Randsholt

Keyword(s):

Drosophila Melanogaster ◽

Ectopic Expression ◽

Polycomb Group ◽

Homeotic Genes ◽

Maternal Control ◽

Gap Gene ◽

Sex Combs ◽

Normal Expression ◽

Selector Genes ◽

Mutant Phenotypes

Abstract We have analyzed the requirements for the multi sex combs (mxc) gene during development to gain further insight into the mechanisms and developmental processes that depend on the important trans-regulators forming the Polycomb group (PcG) in Drosophila melanogaster. mxc is allelic with the tumor suppressor locus lethal (1) malignant blood neoplasm (l(1)mbn). We show that the mxc product is dramatically needed in most tissues because its loss leads to cell death after a few divisions. mxc has also a strong maternal effect. We find that hypomorphic mxc mutations enhance other PcG gene mutant phenotypes and cause ectopic expression of homeotic genes, confirming that PcG products are cooperatively involved in repression of selector genes outside their normal expression domains. We also demonstrate that the mxc product is needed for imaginal head specification, through regulation of the ANT-C gene Deformed. Our analysis reveals that mxc is involved in the maternal control of early zygotic gap gene expression previously reported for some PcG genes and suggests that the mechanism of this early PcG function could be different from the PcG-mediated regulation of homeotic selector genes later in development. We discuss these data in view of the numerous functions of PcG genes during development.

Download Full-text

E(z): a polycomb group gene or a trithorax group gene?

Development ◽

10.1242/dev.122.7.2189 ◽

1996 ◽

Vol 122 (7) ◽

pp. 2189-2197 ◽

Cited By ~ 6

Author(s):

D. LaJeunesse ◽

A. Shearn

Keyword(s):

Polycomb Group ◽

Bithorax Complex ◽

Trithorax Group ◽

Polycomb Group Genes ◽

Enhancer Of Zeste ◽

Selector Genes ◽

Homeotic Selector Genes ◽

Polycomb Group Gene ◽

Anterior Posterior ◽

Homeotic Selector

The products of the Polycomb group of genes are cooperatively involved in repressing expression of homeotic selector genes outside of their appropriate anterior/posterior boundaries. Loss of maternal and/or zygotic function of Polycomb group genes results in the ectopic expression of both Antennapedia Complex and Bithorax Complex genes. The products of the trithorax group of genes are cooperatively involved in maintaining active expression of homeotic selector genes within their appropriate anterior/posterior boundaries. Loss of maternal and/or zygotic function of trithorax group genes results in reduced expression of both Antennapedia Complex and Bithorax Complex genes. Although Enhancer of zeste has been classified as a member of the Polycomb group, in this paper we show that Enhancer of zeste can also be classified as a member of the trithorax group. The requirement for Enhancer of zeste activity as either a trithorax group or Polycomb group gene depends on the homeotic selector gene locus as well as on spatial and temporal cues.

Download Full-text