Eighth Abdominal Segment Research Articles

Expression and embryonic function of empty spiracles: a Drosophila homeo box gene with two patterning functions on the anterior-posterior axis of the embryo.

Using the even-skipped homeo box as a probe to identify diverged homeo box genes in the Drosophila genome, we isolated the empty spiracles (ems) gene. Structural and functional comparisons between ems and other embryonic patterning genes of Drosophila suggest that ems acts, in part, as a homeotic selector gene, specifying the identity of some of the most anterior head segments. Mutant embryos lacking ems protein have severe patterning defects in the anterior head and are missing tracheal structures, including the filzkörper, which are normally developed by the eighth abdominal segment. ems has two different spatial patterns of expression during embryogenesis. The early, head-specific pattern consists of a single anterior stripe at the syncytial and cellular blastoderm stages. The later, metameric pattern consists of bilateral patches of ems expression in neural and ectodermal cells of every head and body segment. Variations of the ems expression pattern in bicoid mutants suggests that the morphogen protein produced by bicoid has a concentration-dependent regulatory role in the establishment of head-specific ems expression. In contrast, the metameric ems pattern is initiated independently of bicoid protein, and ems becomes expressed at high levels in the primordia of the duplicated fïlzkörper that develop in the anterior half of bicoid mutant embryos.

A developmental genetic analysis of the gene Regulator of postbithorax in Drosophila melanogaster

We report the characterization of loss-of-function alleles of the homoeotic mutation Regulator of postbithorax ( Rg-pbx) in Drosophila melanogaster. Rg-pbx is a dominant gain-of-function mutation which shows a transformation of posterior haltere to wing in the adult cuticle. This mutant phenotype mimics that of the bithorax complex lesion postbithorax ( pbx). Loss-of-function alleles described here are lethal in the embryonic stage and affect the pattern of segmentation of the embryo. Examination of the terminal phenotype of null and hypomorphic alleles of Rg-pbx has shown that inactivation of the Rg-pbx gene leads to loss of the thoracic segments and the adjacent labial segment of the Drosophila embryo. An effect of the mutations is also seen in the seventh and eighth abdominal segments of embryos. The loss-of-function phenotype is similar to that described for the segmentation mutant hunchback ( hb). Complementation tests show that Rg-pbx and hb are allelic. Temperature shift experiments using a temperature-sensitive loss-of-function allele show that the Rg-pbx gene product is required early in embryogenesis. We further report that the dominant Rg-pbx phenotype is sensitive to the gene dosage of another segmentation-controlling gene, fushi tarazu ( ftz). Flies carrying a mutant copy of the ftz gene in trans to Rg-pbx show a dramatic enhancement of the penetrance of the homoeotic mutant phenotype. We were also able to demonstrate a suppression of the Rg-pbx phenotype by the addition of a duplication for the ftz + gene to an Rg-pbx stock. Examination of the phenotype of ftz −, Rg-pbx − double-mutant embryos did not reveal a clear pattern of epistasis between the genes nor was absolute additivity of phenotype seen. A possible formal relationship between Rg-pbx, ftz, and the postbithorax ( pbx) locus is proposed.

Expression of homeotic genes in Bombyx mori estimated from asymmetry of dorsal closure in mutant/normal mosaics

AbstractGenetic mosaics of homeotic genes, ENk and ESw, in the silkworm, Bombyx mori, were made using a hereditary mosaic gene, mo. Deformed segmentation, due to asymmetric integumental fusion during dorsal closure, was observed in the mosaics. Left and right integuments that contained an ENk or ESw gene on either side did not fuse symmetrically on the dorsal center line. The asymmetric fusion was observed only in places where the dorsal center lines corresponded to the border line between genotypes. In mosaics of ENk and +E, the sides of segments containing ENk genes frequently fused with anterior parts of the wild‐type side, in the region from the metathorax to the fourth adbominal segment, while on the sixth through eighth abdominal segments they fused with the posterior parts of the opposite sides. In mosaics of ENk and +E, asymmetric fusion was observed in a narrower region, from the metathorax to the second abdominal segment. In this region, the sides containing ESw genes frequently fused with posterior parts of the wild‐type side, in contrast to the fusion observed for ENk mosaics. The cause of asymmetric fusion and expression of the homoeotic genes in degmental differentiation are discussed in terms of a quantitive analysis of the relationship between mosaic patterns and asymmetric patterns of fusion.

The zygotic mutant tailless affects the anterior and posterior ectodermal regions of the Drosophila embryo

The recessive zygotic lethal mutation tailless maps to region 100A5,6-B1,2 at the tip of the right arm of chromosome 3, and results in shortened pharyngeal ridges in the head skeleton of the mature embryo and the elimination of the eighth abdominal segment and telson. Although they have a normal body length, tailless embryos have a smaller number of abdominal segments, some of which are larger than normal. The mutant phenotype is seen as early as 8 hr post-fertilization, when tailless embryos are observed to have fewer tracheal pits than wildtype. At 9 hr, tailless embryos appear to be missing segments A8, A9, and A10 and have an abnormal clypeolabrum, optic lobes, and procephalic lobe. Segments A4, A5, A6, and A7 appear larger in tailless embryos than wildtype at this stage. The tailless mutation, although affecting anterior and posterior ectodermal structures in the mature embryo, does not affect the formation of pole cells, the posterior midgut, or the proctodeum, which arise from the most posterior region of the embryo. The mutation does result, however, in the failure of Malpighian tubule formation. Consistent with its effect on ectodermal segments, tailless leads to a reduction in the number of segmented, paired ganglia in the ventral nerve cord as well as to an abrupt alteration in the posterior region of the tracheal system. The role the tailless gene may play in the formation of the most anterior and posterior regions of the embryo's ectodermal body plan is discussed.

Regulation of the Ultrabithorax gene of drosophila by other bithorax complex genes

The bithorax complex of Drosophila is composed of three major units of gene function, Ultrabithorax ( Ubx), abdominal-A ( abd-A), and Abdominal-B ( Abd-B), each having a precise realm of action within the thorax and abdomen. Recent molecular studies have established that the transcripts and protein products of the Ubx gene are expressed principally in a restricted portion of the body, beginning in the second thoracic segment and ending in the eighth abdominal segment (i.e., in parasegments 5–13). However, within this region, both show complex, heterogeneous patterns of expression. Using mutations in the abd-A, Abd-B, and esc ( extra sex combs) genes we show that these distinct patterns result in large part from regulation of Ubx gene expression by the abd-A and Abd-B gene functions.

DEVELOPMENTAL GENETICS OF THE 2C-D REGION OF THE DROSOPHILA X CHROMOSOME

We have conducted a genetic and developmental analysis of genes within the 2C-D area of the X chromosome. Phenotypes of 33 mutations representing nine adjacent complementation groups including eight recessive lethals and one visible homeotic mutation (polyhomeotic) are described. Germline clonal analysis of the eight zygotic lethals has revealed three types of gene requirements: normal activity at two pupal lethal loci (corkscrew and C204) and one larval lethal locus (ultraspiracle) is required for normal embryogenesis; normal activity at three larval lethal loci (DF967, VE651 and Pgd) is required for normal oogenesis; and activity at only one locus (EA82), a larval lethal, appears to have no maternal requirement. Ambiguous results were obtained for the GF316 lethal complementation group. Analysis of mitotic figures of the pupal lethals indicates that C204 disrupts an essential mitotic function. This result correlates with the preblastoderm arrest observed among embryos derived from germline clones of C204. Embryos derived from germline clones of corkscrew (csw) exhibit a "twisted" phenotype. The recessive lethal ultraspiracle (usp) disrupts the organization of the posterior tip of the larval both zygotically and maternally: second instar usp/Y larvae derived from heterozygous usp/+ mothers possess an extra set of spiracles, whereas usp/Y embryos derived from females possessing a germline clone (usp/usp) exhibit a localized ventral defect in the ninth or posterior eighth abdominal segment. Analysis of the phenotypes of deficiency-hemizygous embryos indicates the presence of an embryonic zygotic lethal locus, as yet unidentified, which produces central nervous system and ventral hypoderm degeneration. Additional information on the genetic organization of loci within the adjacent 2E area are also described.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of Ultrabithorax proteins in Drosophila

We have used a monoclonal antibody to examine the distribution of Ultrabithorax (Ubx) proteins in Drosophila embryos and imaginal discs by immunofluorescence. Ubx proteins are nuclear and show a spatially restricted distribution in the nervous system, epidermis and mesoderm. Labelling extends from the first thoracic segment (T1) to the eighth abdominal segment (A8) in the midline cells, from T2 to A8 in the ventral nervous system and epidermis and from A1 to A8 in the somatic mesoderm. In the nervous systems and epidermis the patterns of labelling exhibit a repeat unit, the Ubx metamere, that is out of phase with the segmental repeat unit. At least in the epidermis this repeat unit appears to extend between anterior-posterior compartment boundaries and consists of a posterior compartment together with the succeeding anterior compartment. The most prominently labelled metamere in the nervous system and epidermis is that comprising the posterior region of T3 and the anterior region of A1. Within each metamere the nuclei are heterogeneously labelled. Clear heterogeneity of labelling is also seen amongst the nuclei of the T3 imaginal discs.

A New Gall Midge of the Genus Resseliella (Diptera : Cecidomyiidae) Inhabiting Resin of the Japanese Cedar, Cryptomeria japonica (Taxodiaceae)

A new gall midge inhabiting resin of the Japanese cedar, Cryptomeria japonica D. DON is described under the name, Resseliella resinicola, and brief notes are given on its bionomics. This species is distinguishable from its relatives by characteristics of the male genitalia, stigmata of the eighth abdominal segment of the larva, spines on the antennal horns, and spinules on the cercal lobes of the pupa. The resin midge is multivoltine. Larvae develop in resin and crawl away from the resin to pupate. Pupation takes place between the bark layers. At least one hymenopterous endoparasitoid is associated with the resin midge, but it has not yet been identified.

Protein products of the bithorax complex in Drosophila

A sequence from the Ubx 5′ exon in the bithorax complex of Drosophila melanogaster was expressed as a fusion protein in bacteria. This protein was used to raise rabbit antisera and monoclonal antibodies. These antibodies detect antigens that, on protein blots and by immunofluorescence on whole mounts of imaginal discs, show the predicted segmental distribution of Ubx products. These products are predominantly, if not totally, localized in the cell nucleus. In the embryonic nervous system nuclei are labeled from the second thoracic segment to the eighth abdominal segment. There is no labeling in homozygous Df bxd 100 embryos.

Role of theesc+gene product in ensuring the selective expression of segment-specific homeotic genes inDrosophila

The product of the extra sex combs+ (esc+) gene is required during embryogenesis for the correct determination of segments in Drosophila. If this product is absent, most segments develop like the normal eighth abdominal segment. Here, I extend previous results (Struhl, 1981a) showing that this phenotype results in large part from indiscriminate expression of the bithorax-complex genes which are normally active only in particular segments of the thorax and abdomen. In addition, I test whether the esc+ gene product is required for the correct expression of other homeotic genes. First, I have examined two genes of the Antennapedia-complex (Sex combs reduced+ and Antennapedia+): I find that both genes are normally required in only some of the body segments, but that in the absence of the esc+ gene product, both appear to function adventitiously in other segments. Second, comparing esc+ and esc- embryos lacking both these genes as well as the bithorax-complex, I find that additional homeotic genes (possibly those normally involved in specifying head segments) appear to be expressed indiscriminately when the esc+ gene product is absent. Finally, I present evidence that the products of the esc+ gene and the Polycomb+ gene (a second gene required for the correct regulation of the bithorax-complex) act independently. On the basis of these results, I propose a tentative outline of the roles and realms of action of all of these genes.

Early Embryogenesis in the Stable Fly (Diptera: Muscidae)1

Early developmental events in the stable fly, Stomoxys calcitrans (L.), as studied by light and scanning and transmission electron microscopy, are described. Cleavage is centrolecithal and typically rapid and synchronous throughout the first nine divisions. From the mass of cleavage nuclei, primary vitellophage nuclei segregate centrally and longitudinally through the embryo at the time of the eighth division; a syncytial blastoderm is completed after the ninth division. Before the inception of cytokinesis after the 13th division, 9 or 10 blastoderm nuclei at the posterior pole typically divide to form a distinctive cap of ca. 36 cells and supply secondary vitellophages. Germ band formation is by invagination of appropriate presumptive areas of the blastoderm. Five transient transverse furrows, anterior to the elongating germ band, consistently characterize the embryo dorsum posterior to the cephalic furrow. There is one pair of tracheal invaginations to each segment from the prothoracic to the eighth abdominal segment. At 30°C, the cellular blastoderm was completed in ca. 2.5 h, and germ band retraction commenced in 9 h.

The life cycle ofPteronarcys scotti(Plecoptera: Pteronarcyidae) from the Southern appalachians, U.S.A.

Abstract Larval and adult Pteronarcys scotti Ricker were collected from a mountain stream in northwestern South Carolina, USA. The pattern of larval growth indicated a semivoltine life cycle. Emergence occurred in April and early May, and small larvae first appeared in May. Sexual dimorphism in adult size was apparent; males were 0.8 as large as females in head capsule width. Female larvae possess a midventral notch on the eighth abdominal segment that can be used to sex larvae as small as 2.5 mm in head width. Female larvae as small as 1 mm in head width have a midventral break in the posterior setal row of segment 8. These characters are illustrated.

Early role of the esc+ gene product in the determination of segments in Drosophila

Recent studies of the esc+ gene suggest that its product acts principally in the initiation, but not the maintenance, of segmental determination. We have tested this hypothesis by examining when the esc+ gene product is required during embryogenesis, and whether the esc+ gene product is required for the stable determination of imaginal disc cells passaged in in vivo culture. We find that the esc+ gene product is required during a discrete period of embryogenesis. If the gene product is absent or inactive during this period, most segments develop like the eighth abdominal segment. In contrast, absence of active gene product before or after this period has relatively little effect on segmental development. These results support the hypothesis that the esc+ gene product has a discrete early function in the initiation of segmental determination.

External sexual characters of larvae of Spodoptera littorails (Boisduval) and S. exempta (Walker) (Lepidoptera: Noctuidae) and their use for sexing live larvae

AbstractExternal sexual characters are described for the larvae of Spodoptera littoralis (Boisd) and S. exempta (Wlk.). The characters on the female consist of two pairs of pits on the ventral surface of the eighth and ninth abdominal segments. These pits are visible under a light microscope and can therefore be used for the accurate sexing of live larvae from the third instar onwards. The first- and second-instar larvae of both species could not be sexed using external characters because of their small size. In the males of both species, there are no obvious external sexual characters until the last instar, and therefore the sexes are most easily separated by the presence or absence of the female characters. Third- to sixth-instar larvae of both species were examined for the presence or absence of the female pits and were then sexed by dissection. The accuracy of sexing using the external characters was 90–98% for S. littoralis and 100% in all cases for S. exempta. The histology of the female pits and their appearance under the scanning electron microscope is described. These pits in the female larvae give rise to the external openings of the adult reproductive system.

Genetic analysis of abnormal male sexual development in Aedes aegypti and Ae. mascarensis backcross progeny.

When male hybrids of Aedes aegypti females and A. mascarensis males were backcrossed to A. aegypti females, 32.8 percent of the male progeny exhibited abnormal sexual development, including failure of the terminalia to rotate, a split sternite of the eighth abdominal segment with partially duplicated telomeres, or feminization that gives rise to sterile intersexes. Observations made on three morphological marker loci and five isozyme loci with characteristic electromorphs in the two parental species suggested that when the sex-determining M locus is derived from A. mascarensis and the chromosome regions including s, LDH, and lDH2 on chromosome 2 and blt and 6PGD on chromosome 3 are homozygous for genes from A. aegypti, the frequency of abnormal sexual development is increased. An even greater percentage of males suffer aberrant development if recombination also occurs between the M and re locus of chromosome 1. The data suggest that genes on chromosome 2 control normal development of the male terminalia, genes on chromosome 3 control sexual differentiation, and the entire process is controlled by genes on chromosome 1 that are linked to, but not identical with, the M locus.

A new genus of Chlidanotini (Lepidoptera, Tortricidae) from New Caledonia, with a key to genera and check‐list of species

Abstract Iconostigma gen.n., with included species tryphaenu sp.n. (typespecies) and morosa sp.n., is described from New Caledonia. A key to males of the world genera and a check‐list of the world species of Chlidanotini are provided. The relationship of the Chlidanotini to the Polyorthini and Hilarographini is discussed, with particular reference to Iconostigma. It is suggested that the hair‐pencils of the eighth abdominal segment, and the invaginations in the male valvae into which each hair‐pencil is inserted, are apomorphic characters which unite these three tribes. Panegyru Diakonoff is transferred to the Tortricini and Polemograptis flavicostana (Walsingham) is transferred to Panegyra, comb.n.Archimaga euplocamis Meyrick is synonymized with Metrernis ochrolina Meyrick, syn.n.

Life stages and taxonomic affinities ofXenochironomus canterburyensis(Chironomidae: Diptera)

Abstract The adult male and female of Xenochironomus canterburyensis (Freeman) are redescribed, and the larva and pupa are described for the first time. The immature stages are obligate, inquiline commensals of the freshwater mussel Hyridella menziesi (Gray) inhabiting the littoral zone of some New Zealand lakes. The labral setae of the larva are modified to form an elongate feeding brush, and the pupa lacks a posterolateral spur on the eighth abdominal segment. X. canterburyensis appears to be closer to X. xenolabis in certain synapomorphic features and in that both are closely associated with a host species.

Scanning electron microscopy of Drosophila melanogaster embryogenesis : III. Formation of the head and caudal segments

The formation of both the anterior most and posterior most segments in higher dipteran embryos involves complex movements of primordia which can be best visualized with the scanning electron microscope. During head formation, the gnathocephalic segments partially involute through the stomodeum. The labial segment forms the floor of the mouth, and the fused maxillary and mandibular segments form the lateral sides of the mouth. The involuted clypeolabrum forms the roof of the mouth. Invaginations of cells for segmentally derived sense organs can be found prior to involution on all the gnathocephalic and thoracic segments as well as on the labrum. The antennal sense organ derives from the lateral surface of the procephalic lobe. Following involution of the mouth parts, the dorsal ridge, which arises just anterior to the first thoracic segment, is drawn over the dorsal procephalic lobe producing the deep dorsal sac. The optic lobes of the brain invaginate anterior to the dorsal ridge just prior to the covering over of the head. The formation of the anal segment is similarly complex. Two rudimentary segments are found posterior to the eighth abdominal segment. During shortening of the germ band, the posterior most segment is drawn around the posterior tip of the embryo to lie ventrally. Two large anal pads form lateral to the anus from this segment. The next segment, following dorsal closure, produces a pair of anal sense organs and a central tuft of setae. Finally, the eighth abdominal segment gives rise to the posterior spiracles. Following dorsal closure these three segments fuse to produce the terminal (anal) segment of the larva.

The hairpencils of the flour moth Ephestia kuehniella

The hairpencils of the Mediterranean flour moth, Ephestia kuehniella Zeller, are tufts of modified scales between the seventh and eighth abdominal segments of the adult males. The fine structure and development of a hairpencil organule is described. A process of the trichogen cell secretes the modified scale and then withdraws, and the cell invaginates forming a microvillous lumen into which pheromone is probably secreted. This lumen communicates with the outside via rows of pores in the hollow scale. The opening of these pores when the moth emerges from the pupal cuticle may be a result of the drying out of the membrane that covered them. The socket of the hairpencil scale is secreted by a tormogen cell.The hairpencils of male Lepidoptera differ in position from family to family, but the organules that compose them seem to share a common structure. Epidermal glands and organules are classified in a scheme that takes account of their mode of development.

Functional Morphology of the Genitalia of Carcharodus Boeticus Stauderi Rev. (Lepidoptera, Hesperiidae)

The male and female genitalia of Carcharodus boeticus stauderi Rev. are described and figured. The function of various parts of the genitalia is described and discussed. It appears that the eighth abdominal sternite of the female has to attain a vertical position to enable the aedeagus to penetrate into the ostium bursae. The firm connection between the male and female genitalia is effected by the valvae of the male clasping a strongly inflated pouch between the seventh and eighth abdominal segment of the female, called the copulative pouch here.