Expression of the Sex combs reduced protein in Drosophila larvae

We have generated a monoclonal antibody that binds specifically to the protein product of the homeotic Sex combs reduced (Scr) gene of Drosophila, and have mapped the patterns of Scr expression in late third instar larvae. Virtually the entire prothoracic leg imaginal disc expresses the gene, although the levels of expression vary in different disc regions. This heterogeneity does not reflect the compartmental domains defined by engrailed gene expression. Expression is also observed in the cells of the humeral and labial discs, and there is a small patch of Scr-expressing cells in the antenna disc. The gene is expressed in adepithelial cells of the three thoracic leg discs, but not in the wing or haltere discs. In the central nervous system, Scr expression is confined to a narrow band of cells in the subesophageal region of the ventral ganglion. The results are discussed with respect to the known genetic requirements for Scr+ function.     

Analysis of the Sequence and Phenotype of Drosophila Sex combs reduced Alleles Reveals Potential Functions of Conserved Protein Motifs of the Sex combs reduced Protein

The Drosophila Hox gene, Sex combs reduced (Scr), is required for patterning the larval and adult, labial and prothoracic segments. Fifteen Scr alleles were sequenced and the phenotypes analyzed in detail. Six null alleles were nonsense mutations (Scr², Scr⁴, Scr¹¹, Scr¹³, Scr^13A, and Scr¹⁶) and one was an intragenic deletion (Scr¹⁷). Five hypomorphic alleles were missense mutations (Scr¹, Scr³, Scr⁵, Scr⁶, and Scr⁸) and one was a small protein deletion (Scr¹⁵). Protein sequence changes were found in four of the five highly conserved domains of SCR: the DYTQL motif (Scr¹⁵), YPWM motif (Scr³), Homeodomain (Scr¹), and C-terminal domain (CTD) (Scr⁶), indicating importance for SCR function. Analysis of the pleiotropy of viable Scr alleles for the formation of pseudotracheae suggests that the DYTQL motif and the CTD mediate a genetic interaction with proboscipedia. One allele Scr¹⁴, a missense allele in the conserved octapeptide, was an antimorphic allele that exhibited three interesting genetic properties. First, Scr¹⁴/Df had the same phenotype as Scr⁺/Df. Second, the ability of the Scr¹⁴ allele to interact intragenetically with Scr alleles mapped to the first 82 amino acids of SCR, which contains the octapeptide motif. Third, Scr⁶, which has two missense changes in the CTD, did not interact genetically with Scr¹⁴.     

Genetic interaction between homoeotic Sex combs reduced and Regulator of bithorax (or trithorax) genes of Drosophila melanogaster

Summary Regulator of bithorax (Rg-bx)^–, or trithorax (trx)^– lethal larvae occasionally show a homoeotic transformation of the dorsal prothorax to mesothoracic structures. This transformation suggests a reduced activity of the Sex combs reduced (Scr) gene on the basis of gene dosage studies, as well as enhanced expression of the phenotypes of the weak Scr ^– alleles in Rg-bx ^– larvae. Morphological observations of adult flies doubly heterozygous for Rg-bx and Scr mutations also suggest the enhancement of an aspect of Scr adult phenotypes. I conclude that the Rg-bx ⁺ gene function is required for the optimal expression of the Scr gene in larval and imaginai cells.     

How Drosophila change their combs: the Hox gene Sex combs reduced and sex comb variation among Sophophora species

SUMMARY Identification of the events responsible for rapid morphological variation during evolution can help understand how developmental processes are changed by genetic modifications and thus produce diverse body features and shapes. Sex combs, a sexually dimorphic structure, show considerable variation in morphology and numbers among males from related species of Sophophora , a subgenus of Drosophila . To address which evolutionary changes in developmental processes underlie this diversity, we first analyzed the genetic network that controls morphogenesis of a single sex comb in the model D. melanogaster . We show that it depends on positive and negative regulatory inputs from proximo-distal identity specifying genes, including dachshund, bric à brac , and sex combs distal . All contribute to spatial regulation of the Hox gene Sex combs reduced (Scr ), which is crucial for comb formation. We next analyzed the expression of these genes in sexually dimorphic species with different comb numbers. Only Scr shows considerable expression plasticity, which is correlated with comb number variation in these species. We suggest that differences in comb numbers reflect changes of Scr expression in tarsus primordia, and discuss how initial comb formation could have occurred in an ancestral Sophophora fly following regulatory modifications of developmental programs both parallel to and downstream of Scr .     

Expression and function of the homoeotic genes Antennapedia and Sex combs reduced in the embryonic midgut of Drosophila

Drosophila homoeotic genes control the formation of external morphological features of the embryo and adult, and in addition affect differentiation of the nervous system. Here we describe the morphogenetic events in the midgut that are controlled by the homoeotic genes Sex combs reduced (Scr) and Antennapedia (Antp). The midgut is composed of two cell layers, an inner endoderm and an outer visceral mesoderm that surround the yolk. Scr and Antp are expressed in the visceral mesoderm but not in the endoderm. The two genes are required for different aspects of the midgut morphogenesis. In Scr null mutant embryos the gastric caeca fail to form. Scr is expressed in the visceral mesoderm cells posterior to the primordia of the gastric caeca and appears to be indirectly required for the formation of the caeca. Antp is expressed in visceral mesoderm cells that overlie a part of the midgut where a constriction will form, and Antp null mutant embryos fail to form this constriction. An ultrastructural analysis of the midgut reveals that the visceral mesoderm imposes the constriction on the endoderm and the yolk. The mesodermal tissue contracts within the constriction and thereby penetrates the layer of the midgut endoderm. Microtubules participate in the morphological changes of the visceral mesoderm cells. The analysis of the expression of Scr in Antp mutant embryos revealed a case of tissue-specific regulation of Scr expression by Antp. In the epidermis, Antp has been shown to negatively regulate Scr, but it positively regulates Scr in the visceral mesoderm.     

Sex combs,allometry, and asymmetry in Drosophila

There has been recent debate about the expected allometry of sexually‐selected traits. Although sexually‐selected traits exhibit a diversity of allometric patterns, signalling characters are frequently positively allometric. By contrast, insect genitalia tend to be negatively allometric, although the allometry of nongenital sexually‐selected characters in insects is largely unknown (with some notable exceptions). It has also been suggested that there should be a negative association between the asymmetry and size of bilaterally‐paired, sexually‐selected traits, although this claim is controversial. We assessed the allometry and asymmetry (fluctuating asymmetry, FA) of a nongenital contact–courtship structure, the sex comb, in replicate populations of three species of Drosophila (we also measured wing FA). Sex combs are sexually‐selected characters used to grasp the female's abdomen and genitalia and to spread her wings prior to and during copulation. Although species differed in the size of the sex combs, all combs were positively allometric, and comb allometry did not generally differ significantly between species or populations. Comb and wing asymmetry did vary across species, although not across populations of the same species. However, FA was trait specific and was never negatively associated with trait size. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 923–934.     

黑腹果蝇的性别控制

性别的形成包括两个过程,即性别决定和性别分化。果蝇的性别控制研究包括性别决定、性别分化、性别鉴定、性别诱导和性别控制5个方面。性别决定是在两种不同发育途径之间的选择,它提供了一个研究基因调控的模式系统。果蝇的性别决定问题已经研究得相当详细［1］。性别分化是使胚胎向着雌性或雄性发育的过程,决定了性别表型。果蝇的性别分化也取得了不少研究成果。近年来,许多重要的性别调控基因已被克隆和鉴定。随着果蝇基因组全序列测定的完成,果蝇的性别控制研究将会更为深入而完善。本文对与黑腹果蝇性别决定和性别分化相关的一些问题进行综述。     

DSP1, a Drosophila HMG protein, is involved in spatiotemporal expression of the homoeotic gene Sex combs reduced

BACKGROUND INFORMATION: The Pc-G (Polycomb group) and trx-G (trithorax group) genes play a key role in the regulation of the homoeotic genes. The homoeotic gene Scr (Sex combs reduced) contained in the Antennapedia complex specifies segmental identity of the labial and prothoracic segments in Drosophila. Regulation of Scr requires the action of different enhancer elements spread over several kilobases. We previously identified an HMGB (high mobility group)-like protein DSP1 (dorsal switch protein 1), which works like a trx-G protein for the normal Scr expression. RESULTS: In the present study, we attempted to characterize the regulatory sequences involved in the maintenance of the Scr activation by DSP1. We report here, using a transgenic line for the Scr10.0XbaI-regulatory element, that lack of DSP1 affects the function of a reporter gene in legs' imaginal discs but not in embryos. We show by immunolocalization that DSP1 is recruited on polytene chromosomes to the insertion site of the transgene. Moreover, using chromatin immunoprecipitation experiments, we identify two regions of 1 kb in Scr10.0XbaI as the main DSP1 targets. CONCLUSION: These results provide strong evidence that the Scr gene expression is influenced by direct interaction between DSP1 and two Scr regulation elements. In addition, our results show that this interaction undergoes dynamic changes during development.     

The Tribolium castaneum ortholog of Sex combs reduced controls dorsal ridge development

Several constitutional chromosomal rearrangements occur on human chromosome 17. Patients who carry constitutional deletions of 17q21.3-q24 exhibit distinct phenotypic features. Within the deletion interval, there is a genomic segment that is bounded by the myeloperoxidase and homeobox B1 genes. This genomic segment is syntenically conserved on mouse chromosome 11 and is bounded by the mouse homologs of the same genes (Mpo and HoxB1). To attain functional information about this syntenic segment in mice, we have generated a 6.9-Mb deletion [Df(11)18], the reciprocal duplication [Dp(11)18] between Mpo and Chad (the chondroadherin gene), and a 1.8-Mb deletion between Chad and HoxB1. Phenotypic analyses of the mutant mouse lines showed that the Dp(11)18/Dp(11)18 genotype was responsible for embryonic or adolescent lethality, whereas the Df(11)18/+ genotype was responsible for heart defects. The cardiovascular phenotype of the Df(11)18/+ fetuses was similar to those of patients who carried the deletions of 17q21.3-q24. Since heart defects were not detectable in Df(11)18/Dp(11)18 mice, the haplo-insufficiency of one or more genes located between Mpo and Chad may be responsible for the abnormal cardiovascular phenotype. Therefore, we have identified a new dosage-sensitive genomic region that may be critical for normal heart development in both mice and humans.     

The multi sex combs gene of Drosophila melanogaster is required for proliferation of the germline

We present a genetic analysis showing that the Drosophila melanogaster gene multi sex combs (mxc; Santamaria and Randsholt 1995) is needed for proliferation of the germline. Fertility is the feature most easily affected by weak hypomorphic mutations of this very pleiotropic locus. Pole cell formation and early steps of gonadogenesis conform to the wild-type in embryos devoid of zygotic mxc ⁺ product. mxc mutant gonad phenotypes and homozygous mxc germline clones suggest a role for mxc ⁺ in control of germ cell proliferation during the larval stages. mxc ⁺ requirement is germ cell autonomous and specific in females, whilst in males mxc ⁺ product is also needed in somatic cells of the gonads. Although mxc can be classified among the Polycomb group (Pc-G) of genes, negative trans-regulators of the ANT-C and BX-C gene complexes, germline requirement for mxc appears independent of a need for other Pc-C gene products, and mxc gonad phenotypes are different from those induced by mutations in BX-C genes. We discuss the possible functions of the mxc ⁺ product which helps to maintain homeotic genes repressed and prevents premature larval haemocyte differentiation and neoplasic overgrowth, but promotes growth and differentiation of male and female gonads.F.D. and O.S. should be considered as equal first authors     

Regulation of larval hematopoiesis in Drosophila melanogaster: a role for the multi sex combs gene

Drosophila larval hematopoietic organs produce circulating hemocytes that ensure the cellular host defense by recognizing and neutralizing non-self or noxious objects through phagocytosis or encapsulation and melanization. Hematopoietic lineage specification as well as blood cell proliferation and differentiation are tightly controlled. Mutations in genes that regulate lymph gland cell proliferation and hemocyte numbers in the body cavity cause hematopoietic organ overgrowth and hemocyte overproliferation. Occasionally, mutant hemocytes invade self-tissues, behaving like neoplastic malignant cells. Two alleles of the Polycomb group (PcG) gene multi sex combs (mxc) were previously isolated as such lethal malignant blood neoplasm mutations. PcG genes regulate Hox gene expression in vertebrates and invertebrates and participate in mammalian hematopoiesis control. Hence we investigated the need for mxc in Drosophila hematopoietic organs and circulating hemocytes. We show that mxc-induced hematopoietic hyperplasia is cell autonomous and that mxc mainly controls plasmatocyte lineage proliferation and differentiation in lymph glands and circulating hemocytes. Loss of the Toll pathway, which plays a similar role in hematopoiesis, counteracted mxc hemocyte proliferation but not mxc hemocyte differentiation. Several PcG genes tested in trans had no effects on mxc hematopoietic phenotypes, whereas the trithorax group gene brahma is important for normal and mutant hematopoiesis control. We propose that mxc provides one of the regulatory inputs in larval hematopoiesis that control normal rates of plasmatocyte and crystal lineage proliferation as well as normal rates and timing of hemocyte differentiation.     

Multiple Allelism of the net Gene in Drosophila melanogaster and Drosophila simulans

Thenetgene mutations are known to cause abnormal pattern of veining in all wing regions except for the first posterior cells. In natural populations of Drosophila melanogaster, the net alleles were identified, which differ in phenotypic expression from standard mutations. The mutants net-extra-analis from a population Belokurikha-2000 have only a single additional vein in the third posterior cell. A line from Chernobyl-1986 population have another nontypical allele net ^Ch86 and shows a lower degree of abnormalities than that usually observed. About 10% of these flies have an additional vein fragment in the first posterior cell. In both males and females ofD. simulans population Tashkent -2001, which exhibit net ^ST91 mutation, a net of additional veins is formed as a specific additional fragment in the first posterior cell. The pattern of veining conferred by alleles net-extra-analis and net ^Ch86 is altered to a lesser extent; these alleles are dominant with respect to alleles net ^2-45 and net ^ST91, which cause more abnormalities. The heterozygotes for alleles net ^ST9 and net ^Ch86 and for Df(2) net ⁶² deletion have an additional fragment in the first posterior cell and show similarly strong deviations from normal wing vein pattern. The naturalnet alleles correspond, presumably, to different molecular gene defects involved into uncertain local interactions with numerous modifying factors and other genes that specify the wing vein pattern.