Homeotic (HOX) gene

Top PDF Homeotic (HOX) gene:

Evolving expression patterns of the homeotic gene Scr in insects

Evolving expression patterns of the homeotic gene Scr in insects

To address this gap, we focused on the homeotic (hox) gene Sex combs reduced (Scr). In insects, Scr functions in two distinct body regions, the head and the thorax. Previous insights from mRNA expression and functional studies have indicated that this gene is crucial in establishing the identity of the labial segment, suppressing wing formation on the prothorax (T1), and directing the development of T1 leg combs (Beeman et al., 1993; Beeman et al., 1989; Curtis et al., 2001; Hughes and Kaufman, 2000; Pattatucci and Kaufman, 1991; Pattatucci et al., 1991; Rogers et al., 1997; Rogers et al., 2002; Shippy et al., 2006). The data on protein expression in two model systems (Drosophila and Tribolium) show that, in general, mRNA patterns closely coincide with the protein pattern (Curtis et al., 2001; Mahaffey and Kaufman, 1987). However, a report in the terrestrial isopod P. scaber has described a difference between mRNA and protein expression patterns of Scr, revealing the existence of post-transcriptional regulation in this species (Abzhanov and Kaufman, 1999). This result highlights the importance of complementing previously published Scr mRNA expression patterns with data on the accu- mulation of SCR protein. In the present study, we utilize a previously described cross-reacting antibody (Abzhanov and Kaufman, 1999; Curtis et al., 2001) to provide data on the protein accumulation of SCR in six hemimetabolous insect species. Our broad sampling encompasses four divergent insect orders (listed from early to late-branching): Thysanura, the firebrat Thermobia domestica; Orthoptera, the cricket Acheta domestica and the grasshopper Schistocerca americana; Dictyoptera, the cock- roach Periplaneta americana and the praying mantis Tenodera aridifolia; and finally Hemiptera, the milkweed bug Oncopeltus fasciatus. Our analysis has revealed the following key aspects of the evolution of SCR patterning in insects: (i) the anterior border of SCR expression starts in the mandibular segment (Thermobia) and moves posterior to the maxillary segment in some lineages (Acheta and Schistocerca) and then shifts even more posterior to the labial segment (Periplaneta, Tenodera and Oncopeltus); (ii) we found two instances (Thermobia, Oncopeltus) in which Scr mRNA is clearly expressed in a defined region (Rogers et al., 1997) but never accumulates protein, similar to the post-tran- scriptional regulatory situation reported in crustaceans (Abzhanov and Kaufman, 1999); (iii) SCR protein expression in T1 legs is very dynamic and can only occasionally be linked to particular morphological structures. Overall, our data suggests that SCR protein accumulation is highly labile and can be gained or lost even in closely related species.
Show more

8 Read more

Transvection and Silencing of the Scr Homeotic Gene of Drosophila melanogaster

Transvection and Silencing of the Scr Homeotic Gene of Drosophila melanogaster

The Sex combs reduced (Scr) gene specifies the identities of the labial and first thoracic segments in Drosophila melanogaster. In imaginal cells, some Scr mutations allow cis-regulatory elements on one chromosome to stimulate expression of the promoter on the homolog, a phenomenon that was named transvection by Ed Lewis in 1954. Transvection at the Scr gene is blocked by rearrangements that disrupt pairing, but is zeste independent. Silencing of the Scr gene in the second and third thoracic segments, which requires the Polycomb group proteins, is disrupted by most chromosomal aberrations within the Scr gene. Some chromosomal aberrations completely derepress Scr even in the presence of normal levels of all Polycomb group proteins. On the basis of the pattern of chromosomal aberrations that disrupt Scr gene silencing, we propose a model in which two cis-regulatory elements interact to stabilize silencing of any promoter or cis-regulatory element physically between them. This model also explains the anomalous behavior of the Scx allele of the flanking homeotic gene, Antennapedia. This allele, which is associated with an insertion near the Antennapedia P1 promoter, inactivates the Antennapedia P1 and P2 promoters in cis and derepresses the Scr promoters both in cis and on the homologous chromosome.
Show more

14 Read more

The regulation of Hox gene expression during animal development

The regulation of Hox gene expression during animal development

Ectopic overexpression of miR-iab-4 in the Drosophila haltere disc leads to a mild, but clear, haltere-to-wing transformation closely reminiscent of a Ubx-like phenotype and it also produces a reduction in Ubx protein levels, indicating that this miRNA can indeed regulate Ubx gene expression during appendage development (Ronshaugen et al., 2005). However, genetic removal of the miR-iab-4/8 locus does not lead to any evident homeotic transformation in the haltere or elsewhere in the developing fly (Bender, 2008; Thomsen et al., 2010). These experiments raise doubts about the biological significance of Hox regulation by miR- iab4/8. However, expression of Ubx protein within the embryonic CNS is markedly increased in miR-iab-4/8 mutants suggesting that miR-iab-4/8 might exert a biologically relevant regulatory function specifically within this tissue (Bender, 2008; Thomsen et al., 2010). A possible explanation for the absence of biological interactions between miR-iab-4/8 and Ubx during early development emerged from the observation that several Drosophila Hox genes undergo developmentally regulated alternative polyadenylation so that longer 3 ⬘ UTR isoforms (i.e. those containing more miRNA target sites) are only expressed within the CNS (Thomsen et al., 2010). This makes it likely that such longer forms are specifically subjected to miR-iab-4/8 repression, whereas shorter isoforms (those expressed at earlier developmental stages) might be immune to miR-iab-4/8 downregulation or segregated to distinct cellular
Show more

13 Read more

The significance of Hox gene collinearity

The significance of Hox gene collinearity

sarily must be active (Akam et al., 1988, Maeda and Karch, 2015). Essential features of Lewis’s model were also found to apply to vertebrate Hox genes. Thus, in situ hybridization studies showed that Hox genes of mice are similarly expressed in partially overlap- ping domains along the head-tail axis, and the location of genes along the chromosome corresponds with the positions of their anterior expression limits along the embryo (Gaunt et al., 1988). It was then realized that the two homeotic gene complexes of Drosophila are, together, homologous with each of the four Hox clusters in mammals, showing that both animal types had inherited them from a single cluster of at least six Hox genes present in their last common ancestor (Fig. 2). This homology was described from analysis of human Hox genes (Boncinelli et al., 1988), and then from mouse (Duboule and Dolle, 1989, Graham et al., 1989). The last common ancestor of arthropods and vertebrates has been named ‘Urbilateria’ (De Robertis, 2008). The four homologous Hox clusters in mammals themselves arose following two rounds of duplication from the single cluster present in basal chordates (Garcia-Fernandez and Holland, 1994). Correspondence between Hox gene chromosomal location and expression was referred to as the collinearity rule (Lewis, 1985), but is now often called the ‘structural collinearity’ (Izpisua-Belmonte et al., 1991) or ‘spatial collinearity’ (Duboule, 2007) rule.
Show more

13 Read more

Initiation, establishment and maintenance of Hox gene expression patterns in the mouse

Initiation, establishment and maintenance of Hox gene expression patterns in the mouse

II.C.2. RA and the establishment of Hox gene expression domains A possible role of RA in modulating the expression domains of the Hox genes during embryogenesis was suggested by Kessel and Gruss (1991). These authors exposed embryos in utero to exogenous RA, and observed posterior homeotic-like transforma- tions in the vertebral column concomitantly with rostral shifts in Hox expression domains. Depletion of endogenous RA has now con- firmed that this or a related compound plays a crucial role during the establishment of the Hox expression domains: while the initial expression of Hoxa1 in the Retinaldehyde dehydrogenase (Raldh2) null embryos was present at a significantly reduced level, complete loss of Hoxa1 expression was observed in 8.5 and 9.5-day mutant embryos (Niederreither et al., 1999). The significant increase in the level of RA generation at the beginning of somitogenesis in the chick (Maden et al., 1998) might, at least in part, correlate with the role of RA in stimulating Hox gene expression in the rostrally extending axial and paraxial expression domains. Strikingly enough, spinal cord and somites were shown to generate very high levels of RA at early somite-stages, while the CNS anterior to the brain/ spinal cord junction (r1 to r6) did not (Maden et al., 1998). RA is present homogeneously within a large domain with a sharp cutoff at the level of r6/r7, rather than as a gradient with a posterior maximum. In order to account for the expression of the most 3’ Hox genes such as Hoxb1 whose transcription is controlled by a RARE- containing regulatory element, at levels of the hindbrain which do not produce RA (anterior to r7), diffusion of RA from the spinal cord into the presumptive hindbrain in the plane of the neuroepithelium was proposed as a possibility, although no such diffusion could be observed when assaying the presence of RA in the tissue (Maden et al., 1998). Alternatively, because the establishment of the early expression domain of Hoxb4
Show more

16 Read more

Vertebrate GAGA factor associated insulator elements demarcate homeotic genes in the HOX clusters

Vertebrate GAGA factor associated insulator elements demarcate homeotic genes in the HOX clusters

involved in higher-order chromatin regulatory mecha- nisms. In Drosophila, multiple elements, such as en- hancers, insulators, and PREs, form regulatory units that determine and maintain the segment-specific expression pattern of the associated homeotic genes. In mammals, the regulatory elements driving colinear activation and maintenance of Hox expression have not been delineated. In this context, GAGA factor associated histone-depleted regions identified in the intergenic stretches between murine Hox genes suggest sites of potential regulatory function that could help demarcate their domains of expression. We have previously characterized a GA-rich intergenic tract between the Evx2 and Hoxd13 genes conserved among mouse, human, and zebrafish and demonstrated its functional conservation as an enhancer blocker in both transgenic flies and cultured human cells [22]. The region encompassing the GA site has also been shown to act as a chromatin domain boundary element at the murine HoxD locus [39]; we have further shown that specifically mutating the GAGA binding sequence abol- ishes its insulator function [22]. We have previously established Th-POK as the vertebrate homolog of dGAF and indicated its potential to bind and regulate Hox clusters [40]. In this work, we have described a marked association of HFRs across the murine Hox clusters with GAF recognition sites and Th-POK binding. These results indicate a strong correlation of HFRs associated with Th-POK binding as a general feature of mammalian Hox gene domain regulation and provide mechanistic insights into the possible role of the mammalian GAGA factor in nucleosome reorganization at the Hox clusters, thereby setting the stage for the binding of regulatory proteins to organize chromatin regulatory activities, including boundaries.
Show more

12 Read more

Investigating the functional significance of evolutionarily conserved protein motifs of the Drosophila melanogaster HOX protein, Sex combs reduced

Investigating the functional significance of evolutionarily conserved protein motifs of the Drosophila melanogaster HOX protein, Sex combs reduced

Bilaterans share a common anterior-posterior (A-P) axis that is patterned by the Homeotic selector (Hox) genes. In Drosophila melanogaster, Hox gene expression in spatially restricted domains along the A-P axis of the embryo determines segmental identity. Identifying the genetic mechanisms of HOX control of development is essential for understanding body patterning in animals. I identified and characterized the role of evolutionarily conserved protein domains of the HOX protein, Sex combs reduced (SCR), in protein function. SCR is required for establishing the identity of both the labial and prothoracic segments. To identify regions of functional importance, 15 Scr point mutant alleles were sequenced and grouped into three allelic classes: null, hypomorphic and hypomorphic-antimorph. Null alleles were nonsense mutations resulting in
Show more

162 Read more

Schmähling, Sigrun
  

(2019):


	Biochemical purification and functional characterization of a novel trithorax-group protein complex.


Dissertation, LMU München: Fakultät für Biologie

Schmähling, Sigrun (2019): Biochemical purification and functional characterization of a novel trithorax-group protein complex. Dissertation, LMU München: Fakultät für Biologie

Proteine der Trithorax-Gruppe (trxG) sind Regulatoren der Gentranskription mit entscheidenden Funktionen in der Entwicklung von Tieren und Pflanzen. Ihre charakteristische Eigenschaft ist es die Transkription von Zielgenen aufrecht zu erhalten, indem sie den Aktivitäten der transkriptionsreprimierenden Proteine der Polycomb-Gruppe (PcG) entgegensteuern. Zusammen bilden PcG- und trxG-Proteine ein ausgewogenes System antagonistisch wirkender Transkriptionsregulatoren, das für die zeitlich und örtlich korrekte Expression entwicklungsregulatorischer Gene im Körperbauplan vielzelliger Organismen verantwortlich ist. Die kanonischen Zielgene des PcG/trxG-Systems in Tieren sind HOX-Gene. HOX-Gene codieren wiederum für Transkriptionsfaktoren, die innerhalb ihrer Expressionsdomänen die Identität von Körperstrukturen determinieren und erhalten. Der Verlust der Funktion von trxG-Proteinen an einem aktiv transkribierten HOX-Gen führt zur „Übernahme“ durch PcG-Proteine, die das betreffende Gen „stilllegen“. Morphologische Anomalien im Körperbauplan, die klassischen homöotischen Phänotypen, sind die Folge. In meiner Doktorarbeit habe ich das trxG-Protein „Absent, small, or homeotic discs 1“ (Ash1) erforscht, das ursprünglich in genetischen Studien anhand seines homöotischen Mutationsphänotyps in Drosophila identifiziert wurde. Auf der molekularen Ebene agiert Ash1 als Histon-Methyltransferase (HMTase), die spezifisch das Lysin 36 des Histons H3 dimethyliert (H3K36me2). Es wird vermutet, dass Ash1 PcG-Proteinen entgegenwirkt, indem es das Chromatin an gemeinsamen Zielgenen mit H3K36me2 modifiziert. Isoliertes Ash1-Protein weist alleine allerdings nur schwache HMTase-Aktivität auf. Strukturstudien haben gezeigt, dass der Zugang zur katalytischen Tasche in Ash1 durch ein autoinhibitorisches Element blockiert wird. Dies lässt vermuten, dass die enzymatische Aktivität von Ash1 über einen unbekannten Mechanismus stimuliert wird, an dem bisher nicht beschriebene Ash1-Bindungspartner beteiligt sein könnten.
Show more

157 Read more

Onychophoran Hox genes and the evolution of arthropod Hox gene expression

Onychophoran Hox genes and the evolution of arthropod Hox gene expression

In Drosophila and to some extent in other arthropods, segmentation is under control of a hierarchic segmentation gene cascade reviewed in [13-15]. This cascade controls the expression of the Hox genes, which in turn specify segmen- tal identity. It is believed that the Hox genes are involved in providing positional information in a combinatorial mode to give each segment its identity along the anterior-posterior body axis [16-19]. Thus, disturbance of the Hox patterning, such as loss-of-function or ectopic expression of Hox genes often results in homeotic transformations, the change of one segment’s identity into that of another [20-23]. Beyond that, Hox genes are believed to be involved in tagmosis, i.e. the grouping of segments into functional units (tagmata) e.g. [24,25]. The Drosophila Hox clusters contain eight Hox genes, but the ancestral arthropod Hox cluster most likely contained ten Hox genes [26,27]. Two of the Drosophila genes, however, have changed their function. These are fushi-tarazu (ftz) and Hox3. The latter gene evolved into bicoid (bcd), zerknüllt (zen), (also referred to as z1) and z2 [28,29]. These genes have lost their homeotic function and now have new expression patterns. In Drosophila, ftz acts as a pair rule gene [30], and bcd/zen-genes are involved in axis determination and formation of extraembryonic membranes [31]. However, in more basally branching arthropods, the expression patterns of Hox3 and ftz are consistent with ca- nonical Hox-like domains [32-36].
Show more

11 Read more

Regulation of mouse Hoxb-4 expression during embryogenesis

Regulation of mouse Hoxb-4 expression during embryogenesis

Recently the mouse MU gene has been disrupted by gene targeting (Yu et a l, 1995). MU is widely expressed from at least 7.0 dpc in the embryo and persists into adulthood. Mll+f- heterozygotes show retarded growth, hematopoietic abnormalities and exhibit bidirectional homeotic transformations of the axial skeleton as well as sternal malformations. In agreement with this phenotype, the anterior boundaries of mesodermal and neural expression of the representative Hox genes, Hoxa-7 and Hoxc-9, are shifted posteriorly by a distance of one to three segmental units. These effects on Hox gene expression are observed as early as 9.5 dpc. The homozygous state {Mll-i-) is embryonic lethal and embryos die midway through gestation. At 10.5 dpc expression of Hoxa-7 and Hoxc-9 was undetectable, despite the presence of normal sites of Hox expression such as somites, neural tube, spinal ganglia and limb buds. The results of these experiments firmly establish a positive regulatory role for MU in Hox gene regulation. However, it is not clear whether MU is required for the initial activation or for the maintenance of H ox gene expression, or both. A similar effect of phenotypic dosage-sensitivity is seen with both MU deficiency and bmi-1 over-expression (van der Lugt et a l, 1994). This provides further evidence that Pc-G and trx-G proteins operate by a mechanism of competitive interaction, as has been suggested for Drosophila (Chang et a l, 1995a; see Chapter 1.2.2). In this respect it would be interesting to see if bmi- 1-I-/MIUI- double mutants exhibit a less severe phenotype than with either mutant alone, as has
Show more

212 Read more

Hox gene function and cell identity in Drosophila

Hox gene function and cell identity in Drosophila

The Drosophila Hox genes are expressed in precise segmental domains (Figure 1.2), suggesting that their downstream targets would also be differentially expressed between segments. Based on this assumption, two studies were undertaken to look for genes specifically activated or repressed in response to ectopic expression of a Hox gene. In the first of these, the expression of enhancer traps was analysed in the developing antenna following misexpression of Antp (Wagner-Bernholz et al., 1991). Enhancer trap lines contain a single copy of a transposon that carries a fusion between lacZ and a basal promoter, which comes under the regulation of enhancer elements close to its random insertion site in the genomic DNA. Thus reporter expression generally reflects the whole, or part of the expression pattern of a neighbouring gene. Wagner-Bernholz and colleagues (1991) used enhancer traps to identify regulatory elements and the corresponding genes under the control of ANTP during the antenna-to-leg homeotic transformation. In a second approach, Feinstein et al. (1995) used subtractive hybridisation to enrich for genes transcribed following ectopic expression of UBX, and thus only isolated genes potentially activated by this HOX protein.
Show more

268 Read more

Wnt signaling is a key mediator of Cdx1 expression in vivo

Wnt signaling is a key mediator of Cdx1 expression in vivo

It is well established that the Hox gene products are crucial mediators of AP vertebral patterning. The 39 murine Hox genes are distributed in four clusters, Hoxa to Hoxd, which are likely to have arisen from duplication of an ancestral complex related to the Drosophila melanogaster homeotic gene complex (HOM-C) (Duboule, 1998; Duboule and Dollé, 1989; Ferrier and Holland, 2001; Lemons and McGinnis, 2006). In the mouse, Hox transcripts are first detected at embryonic day 7.5 (E7.5) in the primitive streak, with expression subsequently expanding to a fixed rostral limit in the neurectoderm and paraxial mesoderm (Kmita and Duboule, 2003; Deschamps and van Nes, 2005). Both the onset and rostral limit of expression are generally related to the chromosomal location of a given Hox gene within a cluster, with 3 ⬘ members expressed earlier and reaching a more anterior limit than their 5 ⬘ counterparts. This results in staggered domains of Hox gene expression along the AP axis, which is believed to comprise a ‘Hox code’ for vertebral patterning (Burke et al., 1995; Gaunt, 1994; Kessel and Gruss, 1991). Grafting experiments in the chick have demonstrated that the cues controlling both vertebral AP patterning and somitic Hox gene expression are acquired early and are fixed in the anterior presomitic
Show more

9 Read more

A comprehensive catalog of post-translational modifications of Drosophila melanogaster HOX protein, Sex combs reduced

A comprehensive catalog of post-translational modifications of Drosophila melanogaster HOX protein, Sex combs reduced

function. Toolkit genes are highly conserved across animal species. The Hox genes provide an example of extensive conservation. Primitive Hox clusters are found in the diploblastic Cnidarian lineage, but not in Ctenophores, Placozoa or Porifera lineages (Murtha et al., 1991; Schierwater et al., 1991; Schummer et al., 1992; Finnerty & Martindale, 1999). A gene cluster called ParaHox is thought to be an evolutionary sister of the Hox gene cluster (Brooke et al., 1998) and exists in Cnidarians and Bilaterans (Finnerty & Martindale, 1999). Both Hox and ParaHox gene clusters are thought to have diverged from a ProtoHox cluster which probably existed in the Bilateran-Cnidarian ancestor (reviewed in Ferrier & Holland, 2001). Hox gene clusters are highly conserved across Bilaterans, from protostomes to deuterostomes (Figure 3). The pattern of Hox gene expression along the A-P axis is conserved among many animal groups (Negre et al., 2005). The spatial collinear expression of Hox genes observed in Drosophila (Duboule, 2007) is also observed in many animal phyla (Barnett & Thomas, 2013; Hughes & Kaufman, 2002; Fröbius et al., 2008) including deuterostomes like echinoderms and cephalochordates (Monteiro & Ferrier, 2006; reviewed in Gaunt, 2015). The requirement of Hox genes in determining segmental identity is conserved among Bilaterans. Loss-of- function mutations in vertebrate Hox genes result in homeotic transformations, which suggests the conservation of requirement of Hox genes. Both viable Hoxa4 and Hoxa5 (orthologs of Drosophila Scr) homozygous mutant mice show homeotic transformation where the 7 th cervical vertebra is transformed to thoracic vertebrate identity (Horan et al.,
Show more

184 Read more

Is Function of the Drosophila Homeotic Gene Ultrabithorax Canalized?

Is Function of the Drosophila Homeotic Gene Ultrabithorax Canalized?

This observation does not, however, necessarily imply that the traits are under control of different genes, as fine structure analy- sis indicates that the same alleles can [r]

14 Read more

Segment specific prevention of pioneer neuron apoptosis by cell autonomous, postmitotic Hox gene activity

Segment specific prevention of pioneer neuron apoptosis by cell autonomous, postmitotic Hox gene activity

In this study, we demonstrate the first example of apoptosis of differentiated neurons in an invertebrate embryo by showing that the Drosophila dMP2 and MP1 pioneer neurons undergo segment-specific apoptosis at a late developmental stage. These neurons are initially generated throughout the VNC (Bossing and Technau, 1994; Doe, 1992; Schmid et al., 1999; Schmidt et al., 1997), extend their axons and perform a critical pioneering role in guiding follower axons (Hidalgo and Brand, 1997; Lin et al., 1995). We have found that at a later stage, dMP2 and MP1 neurons undergo apoptosis only in anterior segments. While neither the generation nor the initial function of these neurons depends on Hox function, their late, segment- specific survival is under homeotic control; the Hox gene Abdominal B (Abd-B) acts in posterior segments in a cell- autonomous and postmitotic fashion to prevent apoptosis of dMP2 and MP1 neurons by repressing two RHG-motif cell death activators, rpr and grim. Our findings provide clear evidence for a cell-autonomous and anti-apoptotic function of a Hox gene in vivo. Furthermore, they identify a novel mechanism linking Hox positional information to axial differences in neuronal architecture by the selective elimination of mature neurons.
Show more

13 Read more

Genetic Analysis of the Bone Morphogenetic Protein-Related Gene, gbb, Identifies Multiple Requirements During Drosophila Development

Genetic Analysis of the Bone Morphogenetic Protein-Related Gene, gbb, Identifies Multiple Requirements During Drosophila Development

We have isolated mutations in the Drosophila melanogaster gene glass bottom boat (gbb), which encodes a TGF-b signaling molecule (formerly referred to as 60A) with highest sequence similarity to members of the bone morphogenetic protein (BMP) subgroup including vertebrate BMPs 5–8. Genetic analysis of both null and hypomorphic gbb alleles indicates that the gene is required in many developmental processes, including embryonic midgut morphogenesis, patterning of the larval cuticle, fat body morphology, and development and patterning of the imaginal discs. In the embryonic midgut, we show that gbb is required for the formation of the anterior constriction and for maintenance of the homeotic gene Antennapedia in the visceral mesoderm. In addition, we show a requirement for gbb in the anterior and posterior cells of the underlying endoderm and in the formation and extension of the gastric caecae. gbb is required in all the imaginal discs for proper disc growth and for specification of veins in the wing and of macrochaete in the notum. Significantly, some of these tissues have been shown to also require the Drosophila BMP2/4 homolog decapentaplegic (dpp), while others do not. These results indicate that signaling by both gbb and dpp may contribute to the development of some tissues, while in others, gbb may signal independently of dpp.
Show more

12 Read more

The lawc Gene Is a New Member of the trithorax-Group That Affects the Function of the gypsy Insulator of Drosophila

The lawc Gene Is a New Member of the trithorax-Group That Affects the Function of the gypsy Insulator of Drosophila

Mutations in the lawc gene result in a pleiotropic phenotype that includes homeotic transformation of the arista into leg. lawc mutations enhance the phenotype of trx-G mutations and suppress the phenotype of Pc mutations. Mutations in lawc affect homeotic gene transcription, causing ectopic expression of Antennapedia in the eye-antenna imaginal disc. These results suggest that lawc is a new member of the trithorax family. The lawc gene behaves as an enhancer of position-effect variegation and interacts genetically with mod(mdg4), which is a component of the gypsy insulator. In addition, mutations in the lawc gene cause alterations in the punctated distribution of mod(mdg4) protein within the nucleus. These results suggest that the lawc protein is involved in regulating the higher-order organization of chromatin.
Show more

11 Read more

Composition and genomic organization of arthropod Hox clusters

Composition and genomic organization of arthropod Hox clusters

As previously reported [24], several instances of Hox gene duplications were identified in Tetranychus. Tet- ranychus harbors two copies of both fushi tarazu and Antennapedia as tandem duplications, not present in other arthropods (Fig.  1). Needleman–Wunsch global alignment of the coding sequence shows the Tu-ftz1 and Tu-ftz2 and Tu-Antp1 and Tu-Antp2 orthologs share 74 and 55 percent identity, respectively, and at the amino acid level 67 and 33 percent identity, respectively (Addi- tional file  7). Phylogenetic analysis of representative arthropod ftz and Antp sequences supports a hypothesis that the Tetranychus ftz and Antp paralogs emerged via lineage-specific duplications (Additional file  8: Figure S2). The percent identity for the Tetranychus duplicate ftz and Antp orthologs is consistent with another well- known tandem gene duplication located in an arthropod Hox cluster; e.g., Tribolium zerknüllt and zerknüllt-2 share 54 % nucleotide identity and 37 % protein identity, respectively. Alignment of the Tetranychus ftz and Antp amino acid sequences suggests either partial duplications of the genes including the homeodomain-containing region, or deletions occurred post-duplication, upstream of the homeodomain in Antp2440 and ftz2530 as the putative coding sequence for both the ftz and Antp dupli- cates is substantially smaller (Additional file  8: Figure S2). Additionally, comparison of RNAseq profiles across four developmental stages (RNASeq from embryonic, larval, nymphal, and adult) reveal both Antp2440 and ftz2530 have markedly lower levels of expression than their respective paralogs (Additional file 9: Table S6). The scorpion genome revealed the presence of two complete Hox clusters (Fig. 1) [70]. Surveys of the remaining non- insect genomes sampled revealed no apparent Hox gene duplications.
Show more

11 Read more

Hox Gene Collinearity May Be Related to Noether’s Theory on Symmetry and Its Linked Conserved Quantities

Hox Gene Collinearity May Be Related to Noether’s Theory on Symmetry and Its Linked Conserved Quantities

4 tail end of the embryo or the limb bud tip e.g. [2, 11]. This nested pattern denoted as Hox Gene Collinearity (HGC) can be easily incorporated in the present representation. In addition the spatial and temporal features of HGC are still intensively studied in several animal species [12 ]. The above particular local transcription of the Hox genes is a very surprising event that proved later to be a universal property widespread to most animal clades where the Hox genes are grouped in clusters [8].

13 Read more

Did homeobox gene duplications contribute to the Cambrian explosion?

Did homeobox gene duplications contribute to the Cambrian explosion?

The ParaHox genes are particularly intriguing. It was noted in the 1990s that some homeobox genes that are not part of Hox gene clusters are especially similar in DNA sequence to Hox genes, and for some time their evolutionary origins remained unclear. Indeed, for three of these genes – Gsx, Xlox (also called Pdx) and Cdx – their DNA sequences are more similar to some Hox genes than many Hox genes are to each other. They are ‘Hox-like, ’ but not in the Hox cluster. The paradox was solved, or at least clarified, in 1998 when we found that these three genes were arranged in their own gene clus- ter, at least in one animal taxon – the cephalochordate amphioxus [2]. Subsequently, clustering of these three genes has also been found in vertebrates (except teleost fish [25]) and in an echinoderm, the sea star Patiria min- iata [26]. The discovery of the gene cluster in amphioxus, together with phylogenetic analysis of Hox and ParaHox sequences, led to our proposal that Hox and ParaHox gene clusters were generated by an ancient gene cluster duplication event, from a hypothetical progenitor ‘Proto- Hoxgene cluster. Further studies in other taxa have added support to this model, with the main issue of con- tention simply being whether the hypothetical ProtoHox gene cluster had two, three or four homeobox genes [27,28]. Not all animals have retained the ParaHox genes in a clustered arrangement, and some taxa have lost par- ticular ParaHox genes, but the original bilaterians must have possessed an intact ParaHox gene cluster. There was also confusion for some years over the timing of the de- duced Hox-ParaHox duplication event, but it is now clear that it was not an event that characterised the bilaterians uniquely, since it occurred before the divergence of cni- darians and bilaterians [29]. The implication is that the origin of Hox genes and the simultaneous origin of ParaHox genes occurred before the origin of the bilater- ian body plan.
Show more

8 Read more

Show all 10000 documents...