Anterior Abdominal Segments Research Articles

Localization of muscarinic acetylcholine receptor-dependent rhythm-generating modules in the Drosophila larval locomotor network.

Mechanisms of rhythm generation have been extensively studied in motor systems that control locomotion over terrain in limbed animals; however, much less is known about rhythm generation in soft-bodied terrestrial animals. Here we explored how muscarinic acetylcholine receptor (mAChR)-modulated rhythm-generating networks are distributed in the central nervous system (CNS) of soft-bodied Drosophila larvae. We measured fictive motor patterns in isolated CNS preparations, using a combination of Ca2+ imaging and electrophysiology while manipulating mAChR signaling pharmacologically. Bath application of the mAChR agonist oxotremorine potentiated bilaterally asymmetric activity in anterior thoracic regions and promoted bursting in posterior abdominal regions. Application of the mAChR antagonist scopolamine suppressed rhythm generation in these regions and blocked the effects of oxotremorine. Oxotremorine triggered fictive forward crawling in preparations without brain lobes. Oxotremorine also potentiated rhythmic activity in isolated posterior abdominal CNS segments as well as isolated anterior brain and thoracic regions, but it did not induce rhythmic activity in isolated anterior abdominal segments. Bath application of scopolamine to reduced preparations lowered baseline Ca2+ levels and abolished rhythmic activity. Overall, these results suggest that mAChR signaling plays a role in enabling rhythm generation at multiple sites in the larval CNS. This work furthers our understanding of motor control in soft-bodied locomotion and provides a foundation for study of rhythm-generating networks in an emerging genetically tractable locomotor system.NEW & NOTEWORTHY Using a combination of pharmacology, electrophysiology, and Ca2+ imaging, we find that signaling through mACh receptors plays a critical role in rhythmogenesis in different regions of the Drosophila larval CNS. mAChR-dependent rhythm generators reside in distal regions of the larval CNS and provide functional substrates for central pattern-generating networks (CPGs) underlying headsweep behavior and forward locomotion. This provides new insights into locomotor CPG operation in soft-bodied animals that navigate over terrain.

Biological aspects of the larva of Sepedophilus testaceus (Coleoptera: Staphylinidae, Tachyporinae): morphology of the posterior abdomen and prey-capture behaviour

ABSTRACT Two aspects of the larval biology of the rove beetle Sepedophilus testaceus (Staphylinidae: Tachyporinae) were investigated, namely the morphology of the posterior abdomen (abdominal apex) and the predatory behaviour of the larvae towards elusive springtails. The larvae move their urogomphi via a single urogomphal muscle. Its presumed antagonist is a cuticular, possibly elastic process that lies below the urogomphus. Additional features of the posterior abdomen include (i) a reduced but well-developed musculature, (ii) segmental exocrine glands of unknown function, and (iii) five rectal diverticula that are externally visible as eversible lobes and that presumably serve as adhesive organs. Segments IX and X deviate from the more anterior abdominal segments in both their external and internal organisation including their equipment with muscles. Comparisons with previous studies suggest that the segmental glands and rectal diverticula are groundplan features of Staphylinidae and Staphyliniformia, respectively. However, the structure and biological relevance of these traits have as yet received little attention. Laboratory-based highspeed videography observations have confirmed that the investigated L3 larvae are predaceous and highly capable of capturing even elusive prey such as springtails with a relatively high success rate of 40%. The larvae attack their prey immediately after accidental contact and detect and localise their exact position via the hair-like sensilla on their antennae and other body parts. Contact with the prey is below threshold, i.e. occurs without releasing the prey’s escape response, and is followed by a rapid grasping movement of about 40 milliseconds on average that is executed by the falciform mandibles of the larva. This is well within the range of the escape response of the springtail.

Partially coupled reaction norms of pupal colour and spot size in a butterfly

Many species cope with heterogeneous environments through adaptive phenotypic plasticity, and plasticity of body colour is a widely used means of minimizing predation risk. Pupal colour in many butterflies is a plastic trait sensitive to pupation substrate, with green and brown pupae primarily formed on leaf and off-leaf substrates respectively. This is thought to be an example of adaptive phenotypic plasticity because the green and brown pupae are better camouflaged against their respective backgrounds. We tested whether pupal ‘spots’—paired circular markings on the anterior abdominal pupal segments of many butterflies—are also phenotypically plastic. Using experiments on the tropical satyrine butterfly Mycalesis mineus, we confirm that pupal spot size is plastic. Because it is known that pupation substrate influences pupal colour in this species, we tested whether substrate also influences pupal spot size. Further, we explored whether there was a correlation between pupal colour and spot size. We tested the effects of pupation substrate and pupal colour on both absolute spot size and spot size relative to body size. Pupal spot size (absolute and relative) was correlated with both pupal colour and pupation substrate. Brown pupae had larger spots, and green pupae formed off-leaf had intermediate sized spots compared to green pupae formed on leaves and brown pupae, the latter of which always formed off-leaf. Thus, the reaction norm of pupal spot size is partially coupled with both pupal colour and pupation substrate in this species. Since pupation substrate in turn influences pupal colour, the correlated traits of pupal colour and pupal spot could comprise a single functional suite, suggesting a developmental link. We speculate that pupal spots may function against predation, but further studies are needed to understand their possible adaptive significance.

Sexually dimorphic blue bands are intrasexual aposematic signals in nonterritorial damselflies

Sexually dimorphic traits in males are thought to evolve via female preference or male–male competition. Alternatively, in species without overt male displays or female mate choice, dimorphic coloration may function as a warning signal to conspecific males thereby avoiding costly harassment. We aimed to determine the function of sexual dimorphic coloration in the damselfly Xanthagrion erythroneurum in which males, but not females, have conspicuous blue bands on the tip of the abdomen. We show that the male blue bands and female black abdomen are chromatically and achromatically discriminable against their natural background. Moreover, the male blue bands and their adjacent abdominal segments generate higher internal contrast than female abdominal segments. We conducted two sets of experiments to test alternative hypotheses that the male blue bands are (1) the target of female mate choice, or (2) an intrasexual aposematic signal to avoid male mating harassment. We hid male blue bands by painting them black and measured female preference between the manipulated and the nonmanipulated (control) males. We found no difference in mating success between the control and manipulated males, thereby rejecting the female preference hypothesis. To test whether the blue bands function as a warning signal, we manipulated the females by painting male-like blue bands on their abdomen and measured the male response to those females relative to control females. Females with artificial blue bands on the terminal abdomen were mated less frequently than control females. However, when we painted blue bands on the anterior abdominal segments, the males did not discriminate between control and painted females. Our study demonstrates that dimorphic coloration advertises the males' unprofitability as mates to conspecifics thereby reducing intrasexual harassment. • Dimorphic male colour evolves by female choice or by male-male interactions. • In damselflies, females did not prefer males with abdominal blue bands. • However, conspicuous blue bands reduced male mating attempts. • Conspicuous male colour here functions as an antiharassment aposematic signal.

Neuroblast pattern and identity in the Drosophila tail region and role of doublesex in the survival of sex-specific precursors

The central nervous system is composed of segmental units (neuromeres), the size and complexity of which evolved in correspondence to their functional requirements. In Drosophila, neuromeres develop from populations of neural stem cells (neuroblasts) that delaminate from the early embryonic neuroectoderm in a stereotyped spatial and temporal pattern. Pattern units closely resemble the ground state and are rather invariant in thoracic (T1-T3) and anterior abdominal (A1-A7) segments of the embryonic ventral nerve cord. Here, we provide a comprehensive neuroblast map of the terminal abdominal neuromeres A8-A10, which exhibit a progressively derived character. Compared with thoracic and anterior abdominal segments, neuroblast numbers are reduced by 28% in A9 and 66% in A10 and are almost entirely absent in the posterior compartments of these segments. However, all neuroblasts formed exhibit serial homology to their counterparts in more anterior segments and are individually identifiable based on their combinatorial code of marker gene expression, position, delamination time point and the presence of characteristic progeny cells. Furthermore, we traced the embryonic origin and characterised the postembryonic lineages of a set of terminal neuroblasts, which have been previously reported to exhibit sex-specific proliferation behaviour during postembryonic development. We show that the respective sex-specific product of the gene doublesex promotes programmed cell death of these neuroblasts in females, and is needed for their survival, but not proliferation, in males. These data establish the terminal neuromeres as a model for further investigations into the mechanisms controlling segment- and sex-specific patterning in the central nervous system.

Spatial accuracy of a rapid defense behavior in caterpillars

Aimed movements require that an animal accurately locates the target and correctly reaches that location. One such behavior is the defensive strike seen in Manduca sexta larva. These caterpillars respond to noxious mechanical stimuli applied to their abdomen with a strike of the mandibles towards the location of the stimulus. The accuracy with which the first strike movement reaches the stimulus site depends on the location of the stimulus. Reponses to dorsal stimuli are less accurate than those to ventral stimuli and the mandibles generally land ventral to the stimulus site. Responses to stimuli applied to anterior abdominal segments are less accurate than responses to stimuli applied to more posterior segments and the mandibles generally land posterior to the stimulus site. A trade-off between duration of the strike and radial accuracy is only seen in the anterior stimulus location (body segment A4). The lower accuracy of the responses to anterior and dorsal stimuli can be explained by the morphology of the animal; to reach these areas the caterpillar needs to move its body into a tight curve. Nevertheless, the accuracy is not exact in locations that the animal has shown it can reach, which suggests that consistently aiming more ventral and posterior of the stimulation site might be a defense strategy.

Shifting clinal patterns of stress resistance traits in Drosophila ananassae

Drosophila ananassae, a desiccation and cold sensitive species, is abundant along the latitudinal gradient of the Indian subcontinent. Analysis of seasonally varying wild-caught flies showed two independent patterns of melanisation: (1) narrow to broad melanic stripes on three anterior abdominal segments only; (2) a novel body color pattern (dark vs. light background). We investigated the degree to which these two melanisation systems vary; first with latitude and secondly among seasons. There is a shallow latitudinal cline for percent striped melanisation as well as for frequency of body color alleles during the rainy season. The frequencies of body color alleles vary significantly across seasons in the northern populations i.e. the light allele occur abundantly (>0.94) during the rainy season while the frequency of the dark allele increases (0.22–0.35) during the dry season causing steeper clines during the dry season. By contrast, the low variations in abdominal stripes showed non-significant changes and the cline was similar across seasons. Furthermore, both types of melanisation patterns showed no plasticity with respect to temperature. The present study also investigated clines related to desiccation, heat and cold stress in D. ananassae females across seasons (rainy and dry) from nine latitudinal populations. The clines for stress related traits changes to steeper and non-linear during the dry season. Thus, latitudinal populations of D. ananassae differ in slope values of clines for stress related traits across seasons. This study reports seasonal changes in latitudinal clines of stress resistance traits as seen in a changing frequency of body color alleles of D. ananassae in northern locality, while in southern localities it remains constant. This is presumably the result of only minor seasonal changes in humidity and temperature in the South, whereas in the North seasonal climatic variability is much higher.

Ultrabithorax confers spatial identity in a context-specific manner in the Drosophila postembryonic ventral nervous system

BackgroundIn holometabolous insects such as Drosophila melanogaster, neuroblasts produce an initial population of diverse neurons during embryogenesis and a much larger set of adult-specific neurons during larval life. In the ventral CNS, many of these secondary neuronal lineages differ significantly from one body segment to another, suggesting a role for anteroposterior patterning genes.ResultsHere we systematically characterize the expression pattern and function of the Hox gene Ultrabithorax (Ubx) in all 25 postembryonic lineages. We find that Ubx is expressed in a segment-, lineage-, and hemilineage-specific manner in the thoracic and anterior abdominal segments. When Ubx is removed from neuroblasts via mitotic recombination, neurons in these segments exhibit the morphologies and survival patterns of their anterior thoracic counterparts. Conversely, when Ubx is ectopically expressed in anterior thoracic segments, neurons exhibit complementary posterior transformation phenotypes.ConclusionOur findings demonstrate that Ubx plays a critical role in conferring segment-appropriate morphology and survival on individual neurons in the adult-specific ventral CNS. Moreover, while always conferring spatial identity in some sense, Ubx has been co-opted during evolution for distinct and even opposite functions in different neuronal hemilineages.

Chromatin insulator and the promoter targeting sequence modulate the timing of long-range enhancer–promoter interactions in the Drosophila embryo

The homeotic genes are essential to the patterning of the anterior-posterior axis along the developing Drosophila embryo. The expression timing and levels of these genes are crucial for the correct specification of segmental identity. The Abdominal-B (Abd-B) gene is first detected in the most posterior abdominal segments at high levels and gradually appears in progressively anterior abdominal segments in lower amounts. Regulatory mutations affecting this expression pattern produce homeotic transformations in the abdomen. The promoter targeting sequences (PTS) from Abd-B locus overcome the enhancer blocking effect of insulators and facilitate long-range enhancer–promoter interactions in transgenic flies (1, 2). In this study, we found that transgene activation by the IAB5 enhancer can be delayed by inserting a 9.5 kb 3′ Abd-B regulatory region containing the Frontabdominal-8 (Fab-8) insulator and the PTS element. We found that the delay is caused by the PTS and an insulator, and it is not specific to the enhancer or the promoter tested. Based on these findings, we hypothesize that the delay of remote enhancers is responsible for the Abd-B expression pattern, which is at least in part due to the regulatory activities of the PTS elements and chromatin boundaries.

<p class="HeadingRunIn"><strong>Redescription of<em> Capitella capitata</em> (Fabricius) from West Greenland and designation of a neotype (Polychaeta, Capitellidae)</strong></p>

Capitella capitata (Fabricius, 1780), the type species of the genus, was originally described from the SW coast of Greenland; however, current definitions of the species are largely based on Eisig (1887), who described specimens from Naples on the Mediterranean coast. Eisig’s excellent account of the morphology of a sexually dimorphic species has subsequently been applied to specimens collected from worldwide locations. C. capitata was considered cosmopolitan in its distribution until J.P. Grassle and others identified numerous sibling species in laboratory culture. A large collection of Capitella from locations along the W, SW, and SE coasts of Greenland was provided by the Zoological Museum, University of Copenhagen (ZMUC). The collections included about 680 specimens with distinctive prostomial, thoracic, and setal morphology that differs from the typical depiction of the species in most faunal accounts. A neotype was selected from an excellent collection of approximately 250 specimens from Mârmorilik on the Affarlikassâ Fjord on the inner Uummannaq Fjord system, north of Disko Bay. All available collections from the ZMUC are believed to belong to the same species, which is here considered to be Arctic and subarctic in distribution. Additional material from the Alaskan Arctic supports this hypothesis. The Greenland species has a short, cup-shaped, wider-than-long prostomium joined to a narrow peristomial ring that is retracted slightly into setiger 1. In most specimens, the first four thoracic setigers gradually increase in size, with setiger 4 being the largest thoracic segment, and then decrease over the next five setigers, with setiger 9 being smaller than subsequent anterior abdominal segments. The thoracic region is thus markedly distinct visually from the abdominal region. Setigers 8–9 typically lack fascicles of notosetae, but 80% of the specimens examined have genital spines and most have copulatory organs that are secretory in nature: they contain numerous small secretion granules but no sperm. Many of these specimens have eggs and larvae within their tubes, suggesting functional hermaphroditism. The present redescription of C. capitata serves to establish a baseline against which the many known but undescribed species can be compared. Previous accounts of C. capitata based on the Eisig concept and largely from boreal and temperate localities should be reevaluated.

Climatic adaptations of body melanisation in Drosophila melanogaster from Western Himalayas

We investigated population divergence in body melanisation in wild samples of Drosophila melanogaster across an elevational gradient (512 - 2202m) in the Western Himalayas. Wild populations are characterized by higher phenotypic variability as compared with laboratory populations. Significant differences in elevational slope values for three posterior abdominal segments (5th, 6th and 7th) in wild versus laboratory populations suggest plastic effects. However, elevational slope values do not differ for the three anterior abdominal segments (2nd, 3rd and 4th). Thus, elevational changes in melanisation include genetic as well as plastic effects. Fitness consequences of within population variability were analyzed on the basis of assorted darker and lighter flies from two highland as well as from two lowland localities. There is lack of correlation of melanisation with body size as well as ovariole number in assorted darker and lighter flies. For each population, darker flies showed higher desiccation resistance, lower rate of water loss, longer copulation duration and greater fecundity as compared with lighter flies. Phenotypic variations in body melanisation can be interpreted in relation with seasonal changes in temperature as well as humidity (Tcv and RHcv) of the sites of origin of populations. Thus, elevational changes in body melanisation may represent genetic response to selection pressures imposed by colder and drier climatic conditions in the Western Himalayas.

Expression of abdominal-A homeotic gene in ants with different abdominal morphologies

In most insect groups, the Hox gene abdominal-A specifies the development of consecutive monotonous anterior abdominal segments. In contrast, the ant family shows pronounced differentiation of the anterior abdominal segments: the first is fused to the thoracic segments, the second, the petiole, is a specialised segment in all ants and the third, the post-petiole, can either take the appearance of a gastric segment (as in the Dolichoderinae) or of a petiole-like segment, (as in the Myrmicinae). Changes in the regulation of the abdominal-A gene are suspected to be instrumental in this morphological differentiation. Previous work has shown that the genomic coding sequences of the abdominal-A gene is nearly identical between all ant subfamilies. Therefore any evolutionary change within the ant family in the developmental activity of abdominal-A is most likely due to a change in gene expression than to a change in the activity of the Abdominal-A protein. Here I present the embryonic expression of the abdominal-A gene in two ant species with different abdominal morphologies. I find that by the late-germ band stage, abdominal-A transcripts are detected in a similar pattern in both species whereas the early patterning of abdominal-A is distinctly different between the two species.

Lopholeucaspis japonica

<i>Lopholeucaspis japonica</i>

Evolution of a transcriptional repression domain in an insect Hox protein.

Homeotic (Hox) genes code for principal transcriptional regulators of animal body regionalization. The duplication and divergence of Hox genes, changes in their regulation, and changes in the regulation of Hox target genes have all been implicated in the evolution of animal diversity. It is not known whether Hox proteins have also acquired new activities during the evolution of specific lineages. Amino-acid sequences outside the DNA-binding homeodomains of Hox orthologues diverge significantly. These sequence differences may be neutral with respect to protein function, or they could be involved in the functional divergence of Hox proteins and the evolutionary diversification of animals. Here, we identify a transcriptional repression domain in the carboxy-terminal region of the Drosophila Ultrabithorax (Ubx) protein. This domain is highly conserved among Ubx orthologues in other insects, but is absent from Ubx in other arthropods and onychophorans. The evolution of this domain may have facilitated the greater morphological diversification of posterior thoracic and anterior abdominal segments characteristic of modern insects.

Development of segments and appendages in embryos of the desert scorpion Paruroctonus mesaensis (Scorpiones: Vaejovidae).

The scanning electron microscope was used to study the changing features of scorpion embryos from the blastula through early stages in the development of appendages. The earliest scorpion fossils (Silurian period) have structures more advanced than the embryos herein, so the possibility is considered that these embryos still retain and display some features indicative of evolutionary patterns in adult pre-Silurian ancestors. The blastodisc stage is followed by a knob-like germinal center that gives rise to most of the embryo body. The germinal center elongates on the ventral surface of the spherical yolk mass. The broad cephalic lobe is first delineated from the following pedipalpal segment. The limbbuds for the pedipalps and anterior walking legs appear, as additional segments are added at a growth zone at the rear of the embryo body. Initially, in the cephalic lobe there are no limbbuds; then the cheliceral buds emerge from the posterior part of the lobe. The stomodeum appears first in the anterior half of the cephalic lobe, but an oral groove forms and the mouth is displaced posteriorly within the groove. This repositioning allows space anteriorly for invagination (semilunar grooves) of epithelium for the brain and medial eyes. The mouth is directed ventrally in all stages of this study. The widespread chelicerae are initially posterior to the mouth, but later move anterior and dorsal to it. Small limbbud bulges on mesosomal segments disappear later and never become protruding appendages. Metasomal segments are produced free from the yolk surface in a ventral flexure beneath the embryo body. The telson starts as two spherical lobes, but later elongates and tapers distally, not yet developing the sharp sting (aculeus) seen in Silurian and all subsequent scorpions. The walking legs are digitigrade, as in most fossil aquatic scorpions. Segments are delineated in the appendages; the chelicerae and pedipalps are divided distally for chela (claw) formation. Bilateral swellings (limbbuds) on the third abdominal segment become larger than the others, indicating the site of pectine formation. The early fin-like pectines are somewhat posterior in the mesosoma, suggesting ancestral swimming, maneuvering, and balancing for the elongate abdomen. The pectinal surface is initially smooth but later transverse striations increase the surface area as a possible respiratory adaptation. Pectinal teeth (present in Silurian and all subsequent scorpions) and forward movement and merging of anterior abdominal segments are not yet evident in embryos of this study.

Precursor structures and evolution of tympanal organs in Lepidoptera (Insecta, Pterygota)

The patterns of scolopal organs and their innervation were studied by the methylene blue method in larvae, pupae and adults of an Yponomeuta species (Yponomeutidae) and of tympanate adult representatives of the Noctuoidea, Geometridae, Drepanidae and Pyraloidea. The studies were focused mainly on the mesothorax, the metathorax and some anterior abdominal segments. In the abdominal tympanal organs of Geometridae, Drepanidae and Pyraloidea, the auditory scolopidia are homologous with the lateral scolopal organs of the first abdominal segment; however, the hearing organs as such evolved independently in the three taxa. The studies confirm that the tympanal organ in the Noctuoidea is derived from the caudal dorsolateral region of the metathorax including its dorsal scolopal organ and the B-cell. The adult scolopal organs are present already in the larvae and are maintained nearly unchanged during metamorphosis to the adult. Only in the Noctuoidea are the three sensory cells of the larval scolopal organs, which become part of the tympanal organs, reduced to one (in Notodontidae) or two (in other Noctuoidea) during metamorphosis. A hypothetical scenario of the evolution of the tympanal organs is outlined.

Muscle pattern diversification in Drosophila is determined by the autonomous function of homeotic genes in the embryonic mesoderm

Muscle diversification in the Drosophila embryo is manifest in a stereotyped array of myofibers that exhibit distinct segment-specific patterns. Here it is shown that the homeotic genes of the Bithorax complex control the identities of abdominal somatic muscles and their precursors by functioning directly in cells of the mesoderm. Whereas Ultrabithorax (Ubx) and abdominal-A (abd-A) have equivalent functions in promoting the formation of particular muscle precursors in the anterior abdominal segments, Abdominal-B (Abd-B) suppresses the development of these same myogenic cells in the posterior region of the abdomen. When expressed in the same mesodermal cells, however, either UBX or ABD-A can override the inhibitory influence of ABD-B, suggesting that these factors may compete in the regulation of common downstream genes. Furthermore, targeted ectopic expression of Ubx or abd-A indicates that these homeotic genes influence muscle cell fates by autonomous action in mesodermal cells. Muscle identity also appears to be sensitive to the level of UBX in myogenic precursors. Finally, these experiments reveal that homeotic cues specific to both the mesoderm and the ectoderm cooperate to specify the pattern of muscle attachment sites.

Noctuidonema guyanense (Nematoda: Aphelenchoididae): Population Profiles on Male and Female Fall Armyworm Moths2

The distribution of Noctuidonema guyanense Remillet and Silvain (Nematoda: Aphelenchoididae) populations on wild female, laboratory-reared female, and wild male moths of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) was determined. Populations of all life stages of N. guyanense were aggregated (P &amp;lt; 0.05) on abdominal segments 7–10 of wild female and moderately infested (&amp;lt;100 nematodes), laboratory-reared female moths. Nematodes also aggregated on abdominal segments 7–10 on heavily infested (&amp;gt;300 nematodes), laboratory-reared female moths, but larger populations of all mobile life stages migrated from posterior to anterior abdominal segments of a host. On wild male moths, N. guyanense populations tended to disperse along the host's abdomen, with significant aggregates of eggs and neonates on abdominal segments 8–10 and smaller aggregates of adults and juveniles on abdominal segments 1–2. Nematodes avoided colonization of the head of nearly all hosts of either sex.

Interactions of the Drosophila gap gene giant with maternal and zygotic pattern-forming genes

The Drosophila gene giant (gt) is a segmentation gene that affects anterior head structures and abdominal segments A5-A7. Immunolocalization of the gt product shows that it is a nuclear protein whose expression is initially activated in an anterior and a posterior domain. Activation of the anterior domain is dependent on the maternal bicoid gradient while activation of the posterior domain requires maternal nanos gene product. Initial expression is not abolished by mutations in any of the zygotic gap genes. By cellular blastoderm, the initial pattern of expression has evolved into one posterior and three anterior stripes of expression. The evolution, position and width of these stripes are dependent on interactions between gt and the other gap genes. In turn, gt activity in these domains affects the expression of the other gap genes. These interactions, typical of the cross-regulation previously observed among gap genes, confirm that gt is a member of the gap gene class whose function is necessary to establish the overall pattern of gap gene expression. After cellular blastoderm, gt protein continues to be expressed in the head region in parts of the maxillary and mandibular segments as well as in the labrum. Expression is never detected in the labial or thoracic segment primordia but persists in certain head structures, including the ring gland, until the end of embryonic development.

Cis-acting control elements for Krüppel expression in the Drosophila embryo.

Krüppel (Kr), a gap gene of Drosophila, shows complex spatial patterns of expression during the different stages of embryogenesis. In order to identify cis-acting sequences required for normal Kr gene expression, we analysed the expression patterns of fusion gene constructs in transgenic embryos. In these constructs, bacterial lacZ expression was placed under the control of Kr sequences in front of a basal promoter. We identified cis-acting Kr control units which drive beta-galactosidase expression in 10 known locations of Kr expression in early and late embryos. More than one cis-regulatory element drives the expression in the anterior domain at the blastoderm stage, in the nervous system, the midline precursor cells and in the amino-serosa. In addition, two cis-acting elements direct the first zygotic expression of Kr in a striped subpattern within the central region of the blastoderm embryo. Both elements respond to alterations in the activities of maternal organizer genes known to be required for Kr expression in establishing the thoracic and anterior abdominal segments in the wild-type embryo.