Compartments in the wing of Drosophila: A study of the engrailed gene

It has recently been suggested that the wildtype alleles of homeotic genes are responsible for controlling the development of compartments. Because the mutation engrailed gives the posterior wing compartment anterior characteristics, it can be regarded as such a homeotic gene. Our experiments confirm the role of the engrailed gene in development of the posterior wing compartment, results which strongly support and extend the compartment hypothesis.Clonal analysis reveals that the state of the engrailed gene is immaterial to the entire anterior compartment, and crucial to the normal development of the posterior compartment, where it controls the pattern of veins and bristles. The presence of a straight and precisely positioned compartment border is dependent on the activity of the engrailed gene until late in development. We suggest that this is due to the gene's effects on cell affinities of the posterior compartment.The engrailed mutation increases the size and changes the shape of the posterior compartment. engrailed clones cause local wing enlargement only if they are dorsal and include the posterior margin of the wing. Wildtype cells outside the clone contribute to this change of shape. This result suggests that the postero-dorsal margin is primarily responsible for the control of shape, and that the ventral compartment is, to some extent, modeled on the dorsal.     

Controlling growth of the wing: Vestigial integrates signals from the compartment boundaries

In the past few years it has become apparent that the anterior/posterior (A/P) and dorsal/ventral (D/V) compartmant boundaries serve as the source of longrange signals that organize the A/P and D/V axes of the Drosophila wing. Recent work suggests that the vestigial gene may function as a nodal point through which the growth-controlling activity of these two patterning systems is integrated⁽¹⁾.     

Drosophila wing development in the absence of dorsal identity

The developing wing disc of Drosophila is divided into distinct lineage-restricted compartments along both the anterior/posterior (A/P) and dorsal/ventral (D/V) axes. At compartment boundaries, morphogenic signals pattern the disc epithelium and direct appropriate outgrowth and differentiation of adult wing structures. The mechanisms by which affinity boundaries are established and maintained, however, are not completely understood. Compartment-specific adhesive differences and inter-compartment signaling have both been implicated in this process. The selector gene apterous (ap) is expressed in dorsal cells of the wing disc and is essential for D/V compartmentalization, wing margin formation, wing outgrowth and dorsal-specific wing structures. To better understand the mechanisms of Ap function and compartment formation, we have rescued aspects of the ap mutant phenotype with genes known to be downstream of Ap. We show that Fringe (Fng), a secreted protein involved in modulation of Notch signaling, is sufficient to rescue D/V compartmentalization, margin formation and wing outgrowth when appropriately expressed in an ap mutant background. When Fng and alphaPS1, a dorsally expressed integrin subunit, are co-expressed, a nearly normal-looking wing is generated. However, these wings are entirely of ventral identity. Our results demonstrate that a number of wing development features, including D/V compartmentalization and wing vein formation, can occur independently of dorsal identity and that inter-compartmental signaling, refined by Fng, plays the crucial role in maintaining the D/V affinity boundary. In addition, it is clear that key functions of the ap selector gene are mediated by only a small number of downstream effectors.     

Correlation between adult transformation and aldehyde oxidase staining pattern in wing discs ofApterous genotypes inDrosophila melanogaster

Summary The aldehyde oxidase staining pattern in wing discs ofDrosophila melanogaster bearing the genotypesap ^blt /ap ^blt andap ^blt andap ^blt /ap ⁷³ⁿ showns changes from the wild-type pattern. Extensive areas of the presumptive dorsal posterior wing blade, which are normally unstained, have enzyme activity in these mutants. In wings of these genotypes, dorsal posterior structures are replaced by dorsal anterior wing structures. A strong correlation has been found between the frequencies of various staining patterns in the discs and the extent of transformation in the cuticular structures of the wing, which is consistent with the idea that aldehyde oxidase activity can be used as an indicator in the wing disc of this transformation. Unlike the homoeotic mutationengrailed, apterous has not been interpreted as a selector gene yet the work reported here shows thatapterous alleles can cause changes resembling those of theengrailed phenotype both in aldehyde oxidase staining behaviour and in the cuticular transformation.     

Developmental Analysis of the Wing Disc in the Mutant Engrailed of DROSOPHILA MELANOGASTER

The engrailed (en) mutation leads to the transformation of the posterior structures of the dorsal mesothoracic disc into those characteristic of the anterior region of the same disc. Similar posterior-anterior duplications have been detected in dorsal as well as ventral structures of all the thoracic segments. —Genetic combinations of en with other pattern mutants have shown their synergistic effect on the posterior wing pattern.—A clonal analysis of the en wing disc shows that en affects its development in a characteristic way. The genetic change, by induced mitotic recombination, of en⁺ into en cells is followed by the corresponding transformation, except when it takes place some cell divisions prior to differentiation.—The en posterior wing disc cells show positive affinities with normal anterior wing disc cells in aggregates.—The mode of action of the en⁺ locus controlling wing disc development is discussed.     

Transdetermination in the homeotic eye--antenna imaginal disc of Drosophila melanogaster

The effects of homeotic mutations on transdetermination in eye-antenna imaginal discs of Drosophila melanogaster were studied. After 12 days of culture in vivo, antenna discs transformed to ventral mesothorax by AntpNs or AntpZ, transdetermined to notum and wing structures four to five times more frequently than the corresponding wild-type antenna discs. Likewise, eye discs transformed to dorsal mesothorax by eyopt transdetermined to leg structures, also extremely frequently (90%). It seems that, during culture, homeotic antenna as well as homeotic eye discs tend to complete the structural inventory of the mesothoracic segment. Transdetermination in the homeotic disc parts is interpreted as a regeneration process which reestablishes an entire segment, i.e., the ventral mesothoracic portion (leg) in the antenna disc regenerates dorsal mesothoracic parts, and the dorsal mesothoracic portion in the eye disc (wing) regenerates ventral mesothoracic parts, respectively. This implies that antenna and leg discs (ventral qualities) as well as eye and wing discs (dorsal qualities) are serially homologous. The transdetermination frequency of the untransformed eye disc to notum and wing structures is enhanced by Antp to the same extent as is the transdetermination frequency of the antenna disc. The first allotypic wing disc structure formed by the eye disc is notum, followed by structures of the anterior wing compartment and finally by posterior wing structures. No evidence for such a sequence was found in the transdetermination pattern of the antenna disc.     

Clonal analysis of the undifferentiated wing disk of Drosophila

Using a new cell marker, we have examined the early clonal restrictions in wing imaginal disks from late third instar larvae of Drosophila. Large clones do not significantly alter the gross structure of the disks, allowing us to map the clones relative to morphological landmarks. Clones in the posterior region of the disks behave in a similar way to clones in the adult cuticle; that is, they appear to be restricted to a defined compartment, and the presumptive anterior/posterior compartment border defined by these clones is located in a similar place in every disk. In contrast, clones in the anterior region of the wing disks often cross into the region normally occupied by the posterior compartment and, especially near the margins of the disk, show no common posterior boundary. We believe that the anterior clones are “pushing” the anterior/posterior compartment border, and that this pushing is related to the growth advantage of the marked cells, which are Minute⁺ in a Minute background. Finally, we find that clones do not cross between the adepithelial cells, which contribute to the adult musculature, and the disk epithelium.     

Fringe: defining borders by regulating the notch pathway.

The Notch pathway mediates cell-cell interaction in many developmental processes. Multiple proteins regulate the Notch pathway, among these are the products of the fringe genes. The first fringe gene was identified in Drosophila, where it is involved in the formation of the dorsal/ventral border of the wing disc. It has now been found to be crucial for determining the dorsal/ventral border of the Drosophila eye. In vertebrates, fringe genes play roles in the formation of the apical ectodermal ridge, the dorsal/ventral border in the limb bud, and in the development of somitic borders. The roles of fringe in the neural tube or the eyes of vertebrate embryos are not clear, although it is unlikely that these roles are evolutionarily related to those in the same tissues in Drosophila. Genetic evidences suggest that Fringe protein functions by modulating the Notch signaling pathway, perhaps through differential regulation of Notch activation by different ligands; however, the mechanism underlying Fringe function remains to be investigated.     

曲靖西冲鱼(Xichonolepis qujingensis)化石的新材料及对其某些形态特征的讨论

<正> 曲靖西冲鱼(Xichonolepis qujingensis P'an et Wang)是1978年潘江、王士涛二同志为胴甲鱼建立的一个属种。化石产在云南曲靖翠峰山徐家冲与西冲之间中泥盆统海口组的下部。建立这一属种的标本有躯甲上一件骨片的内、外印模(原作者认为系前中背片)和若干属于头甲和胸鳍甲某些散落骨片的内、外印模,材料不多,保存也不甚完好。本文系对曲靖西冲鱼形态特征的补充记述,标本是刘玉海、王俊卿和笔者等自1962年以来陆续在滇东中泥盆统采获的。最初,在武定赵家庄后山的泥灰岩层与刘氏滇鱼     

Regulation and metamorphosis of the abdominal histoblasts ofDrosophila melanogaster

Summary The development of the adult abdomen ofDrosophila melanogaster was analyzed by histology, microcautery, and genetic strategies. Eight nests of diploid histoblasts were identified in the newly hatched larva among the polytene epidermal cells of each abdominal segment: pairs of anterior dorsal, posterior dorsal, and ventral histoblast nests and a pair of spiracular anlagen. The histoblasts do not divide during larval life but begin dividing rapidly 3 h after pupariation, doubling every 3.6 h. Initially they remain confined to their original area, but 15 h after pupariation the nests enlarge, and histoblasts replace adjacent epidermis cell by cell. The histoblasts cover half the abdomen by 28 h after pupariation and the rest by 36 h. Polytene epidermal cells of the intersegmental margin are replaced last. Cautery of the anterior dorsal nest caused deletion of the whole corresponding hemitergite, whereas cautery of the posterior dorsal nest caused the deletion of the macrochaetae of the posterior of the hemitergite. Cautery of the ventral nest deleted the hemisternite and the pleura, whereas cautery of the spiracular anlagen deleted the spiracle. Results of cautery also revealed that no macrochaetae formed on the tergite in the absence of adjacent microchaetae. Clonal analysis revealed that there were no clonal restrictions within a hemitergite at pupariation. Cautery of polytene epidermal cells other than those of the intersegmental margin failed to affect tergite development. However, cautery of polytene epidermal cells of the intersegmental margin adjacent to either dorsal histoblast nest caused mirror-image duplications of the anterior or posterior of the hemitergite in 10% of the hemitergites. Forty percent of the damaged presumptive hemitergites formed complete hemitergites, indicating extensive pattern regulation and regeneration. Pattern duplication and regeneration were accounted for in terms of intercalation and a model of epimorphic pattern regulation (French et al., 1976). Histoblasts in adjacent segments normally develop independently, but if they are enabled to interact by deleting the polytene epidermal cells of the intersegmental margin, they undergo intercalation which results in duplication or regeneration. The possible role of the intersegmental margin cells of insects in development was analyzed.     

Respiratory system of the primitive moth Micropterix calthella (Linnaeus) (Lepidoptera : Micropterigidae)

The 1st thoracic spiracular atrium is closed by anterior and posterior muscle fibres extending between its dorsal and ventral wall. The 2nd thoracic spiracle has only a single (anterior) closing lip, movable by a muscle inserting on the wall below the spiracular aperture; this configuration may be a lepidopteran ground-plan autapomorphy. There are functional spiracles on abdominal segments I – VII, each with a closing “bow” and “lever”. There are intrinsic occlusor muscles in all abdominal spiracles and the 1st spiracle has an extrinsic (ventral) dilator. Dorsal dilator muscles or ligaments are absent. A dorsal and a ventral tracheal trunk extend from the 1st thoracic spiracle into the head; the latter supplies the mouthparts and the antenna; there is no connection between the dorsal and ventral cephalic trunk systems. There is a single series of lateral connectives between the spiracles of each side. There is a ventral tracheal commissure in both pterothoracic segments, but none in the prothorax. In each pterothoracic segment an anterior and a posterior tracheal arch give off branches to the wing and anastomose with each other on their downwards course into the leg. Wing tracheation is greatly reduced. The anterior and posterior tracheae of each wing are independent of each other. There is a dorsal commissure in abdominal segment VIII; ventral abdominal commissures are lacking in Micropterix, although present in other micropterigid genera. The terminalia are partly supplied from tracheae arising in segment VII. Air sacs occur in the tibiae only. Phylogenetic aspects of holometabolan tracheation patterns are discussed.     

Restoration of wing margins in Lyra mutants of Drosophila melanogaster

Lyra is a dominant, homozygous lethal mutation of Drosophila melanogaster; in heterozygotes the wings lack portions of the anterior and posterior margins including the characteristic bristles. We have found that, in addition to the loss of bristle forming cells, there is a decrease in the number of wing surface cells that varies between 10 and 20%. However, we observed no histological evidence of excessive cell death in either the larval discs or the pupal wing precursors in Lyra flies. Restoration of all or part of the normal wing margins occurs in some, but not all, cases of morphogenetic mosaics, in which there were patches of wild-type cells in Lyra wing margins due to irradiation-induced mitotic recombination. Analysis of these restorations, using margin bristles as indicators, shows that the Lyra wild-type gene is not involved in bristle formation per se and further that its expression is not cell autonomous. Instead the effect of the Lyra mutation appears to be associated with development of a margin forming subpopulation of cells and to influence the characteristic pattern of cells and bristles in the wing margin via an inductive interaction. The dorsal-ventral boundary can be demonstrated in the de facto wing margins of Lyra mutants suggesting that its origin is independent of any function Lyra might have in normal wing margin morphogenesis. In wing margin restorations the dorsal-ventral boundary is clearly delimited by trichomes and somewhat less rigorously shown by the margin bristles. Further, in these restorations ventral clones induce dorsal bristles, as well as ventral ones, and vice versa, indicating that the influence of Lyra is not restricted by the dorsal-ventral boundary.     

Cell death and selective adhesion reorganize the dorsoventral boundary for zigzag patterning of Drosophila wing margin hairs

Animal tissues and organs are comprised of several types of cells, which are often arranged in a well-ordered pattern. The posterior part of the Drosophila wing margin is covered with a double row of long hairs, which are equally and alternately derived from the dorsal and ventral sides of the wing, exhibiting a zigzag pattern in the lateral view. How this geometrically regular pattern is formed has not been fully understood. In this study, we show that this zigzag pattern is created by rearrangement of wing margin cells along the dorsoventral boundary flanked by the double row of hair cells during metamorphosis. This cell rearrangement is induced by selective apoptosis of wing margin cells that are spatially separated from hair cells. As a result of apoptosis, the remaining wing margin cells are rearranged in a well-ordered manner, which shapes corrugated lateral sides of both dorsal and ventral edges to interlock them for zigzag patterning. We further show that the corrugated topology of the wing edges is achieved by cell-type specific expression and localization of four kinds of NEPH1/nephrin family proteins through heterophilic adhesion between wing margin cells and hair cells. Homophilic E-cadherin adhesion is also required for attachment of the corrugated dorsoventral edges. Taken together, our results demonstrate that sequential coordination of apoptosis and epithelial architecture with selective adhesion creates the zigzag hair alignment. This may be a common mechanism for geometrically ordered repetitive packing of several types of cells in similarly patterned developmental fields such as the mammalian organ of Corti.     

Interhemispheric connections through the pallial commissures in the brain of Podarcis hispanica and Gallotia stehlinii (Reptilia,Lacertidae)

The cells-of-origin and the mode and site of termination of the interhemispheric connections passing through the anterior and posterior pallial commissures in the telencephalon of two lizards (Podarcis hispanica and Gallotia stehlinii) were investigated by studying the anterograde and retrograde transport of unilaterally injected horseradish peroxidase. The commissural projections arise mainly from pyramidal cells in the medial, dorsomedial, and dorsal cortices (medial subfield). Additionally some non-pyramidal neurons in the medial and dorsal cortices contribute to the commissural system. Medial cortex neurons project to the contralateral anterior septum through the anterior pallial commissure. The dorsomedial cortex projects contralaterally via the anterior pallial commissure to the dorsolateral septum and to the medial, dorsomedial, and dorsal cortices. The projection to the medial cortex terminates in two bands at the inner and outer border, respectively, of the cell layer; the projection to the dorsomedial and dorsal cortex ends in a zone in layer 1 which previously has been described to be Timm-negative, and in a diffuse band in the inner half of layer 3. The medial subfield of the dorsal cortex projects through the anterior pallial commissure to the dorsomedial and dorsal cortices with a similar pattern of termination to that found for the dorsomedial cortex. The posterior pallial commissure contains only the projections from the ventral cortex to its contralateral counterpart and to the ventral part of the caudal medial cortex. The similarities found between this commissural system and the mammalian hippocampal interhemispheric connections are discussed.     

Three-dimensional reconstruction of the musculature of Cossura pygodactylata Jones, 1956 (Annelida: Cossuridae)

The musculature of adult specimens of Cossura pygodactylata was studied by means of F-actin labelling and confocal laser scanning microscopy (CLSM). Their body wall is comprised of five longitudinal muscle bands: two dorsal, two ventral and one ventromedial. Complete circular fibres are found only in the abdominal region, and they are developed only on the border of the segments. Thoracic and posterior body regions contain only transverse fibres ending near the ventral longitudinal bands. Almost-complete rings of transverse muscles, with gaps on the dorsal and ventral sides, surround the terminal part of the pygidium. Four longitudinal bands go to the middle of the prostomium and 5–14 paired dorso-ventral muscle fibres arise in its distal part. Each buccal tentacle contains one thick and two thin longitudinal muscle filaments; thick muscle fibres from all tentacles merge, forming left and right tentacle protractors rooted in the dorsal longitudinal bands of the body wall. The circumbuccal complex includes well-developed upper and lower lips. These lips contain an outer layer of transverse fibres, and the lower lip also contains inner oblique muscles going to the dorsal longitudinal bands. The branchial filament contains two longitudinal muscle fibres that do not connect with the body musculature. The parapodial complex includes strong intersegmental and segmental oblique muscles in the thoracic region only; chaetal retractors, protractors and muscles of the body wall are present in all body regions. Muscle fibres are developed in the dorsal and ventral mesenteries. One semi-circular fibre is developed on the border of each segment and is most likely embedded in the dissepiment. The intestine has thin circular fibres along its full length. The dorsal blood vessel has strong muscle fibres that cover its anterior part, which is called the heart. It consists of short longitudinal elements forming regular rings and inner partitions. The musculature of C. pygodactylata includes some elements that are homologous with similar muscular components in other polychaetes (i.e., the body wall and most parapodial muscles) and several unique features, mostly at the anterior end.     

Cell lineage: Compartments and Capricious

Until recently, little was known about the mechanisms that prevent cell migration across compartment boundaries in Drosophila. A new report suggests that the lineage restriction between the dorsal and ventral compartments of the developing wing relies in part on the transmembrane proteins, Capricious and Tartan.     

Heart formative factor(s) is localized in the anterior endoderm of early Xenopus neurula

To elucidate the mechanisms of early heart morphogenesis in Xenopus laevis, we examined the effect of endoderm on heart morphogenesis in the early Xenopus neurula. Explants of anterior ventral (presumptive heart) mesoderm from early neurula were cultured alone or in combination with endoderm dissected from various regions. Heart formation was scored by an original heart index based on morphology. These explant studies revealed that anterior ventral endoderm plays a critical role in heart morphogenesis. Furthermore, we found that it was possible to confer this heart-forming ability on posterior ventral endoderm by the injection of poly(A)⁺ RNA from stage 13 anterior endoderm. These results imply that the heart formative factor(s) is localized in the anterior endoderm of the early neurula and that at least part of this activity is encoded by mRNA(s).     

Immunocytochemical localization of somatostatin and vasotocin in the brain of the Pacific hagfish,Eptatretus stouti

Summary The brain of the Pacific hagfish, Eptatretus stouti, was studied immunocytochemically using antisera against somatostatin (SRIH), arginine vasopressin (AVP), and adrenocorticotropic hormone (ACTH). SRIH-immunoreactive perikarya were distributed bilaterally in the postoptic nucleus and in the hypothalamic nucleus. Although several short, stained fibers were observed in the vicinity of the perikarya, SRIH-immunoreactivity was not found in the neurohypophysis, nor in other parts of the brain. On the other hand, presumed arginine vasotocin (AVT) perikarya were distributed in an arc-shaped region extending from the posterior part of the preoptic nucleus to the anterior-most end of the hypothalamic nucleus and projected their fibers to the neurohypophysis. Most presumptive AVT perikarya were located close to the paired prehypophysial arteries near the anterior end of the postoptic nucleus. In the neurohypophysis, abundant presumptive AVT-fibers terminated in the posterior dorsal wall, although some fibers terminated in the anterior dorsal wall and only a few fiber endings were found in the ventral wall. No ACTH-positive cells were detected in the hagfish brain or in the pituitary gland.Supported from a grant from the National Science Foundation PCM 8141393     

The wings ofBombyx mori develop from larval discs exhibiting an early differentiated state: a preliminary report

Lepidopteran insects present a complex organization of appendages which develop by various mechanisms. In the mulberry silkworm,Bombyx mori a pair of meso- and meta-thoracic discs located on either side in the larvae gives rise to the corresponding fore- and hind-wings of the adult. These discs do not experience massive cell rearrangements during metamorphosis and display the adult wing vein pattern. We have analysed wing development inB. mori by two approaches, viz., expression of patterning genes in larval wing discs, and regulatory capacities of larval discs following explantation or perturbation. Expression of Nubbin is seen all over the presumptive wing blade domains unlike inDrosophila, where it is confined to the hinge and the wing pouch. Excision of meso- and meta-thoracic discs during the larval stages resulted in emergence of adult moths lacking the corresponding wings without any loss of thoracic tissues suggesting independent origin of wing and thoracic primordia. The expression of wingless and distal-less along the dorsal/ventral margin in wing discs correlated well with their expression profile in adultDrosophila wings. Partially excised wing discs did not showin situ regeneration or duplication suggesting their early differentiation. The presence of adult wing vein patterns discernible in larval wing discs and the patterns of marker gene expression as well as the inability of these discs to regulate growth suggested that wing differentiation is achieved early inB. mori. The timings of morphogenetic events are different and the wing discs behave like presumptive wing buds opening out as wing blades inB. mori unlike evagination of only the pouch region as wing blades seen inDrosophila.     

Components of positional information in the developing wing margin of the Lyra mutant of Drosophila

Summary A number of parameters characteristic of the wing margin precursor in imaginal discs of Drosophila are known: the zone of non-proliferating cells or ZNC (O'Brochta and Bryant 1985), aldehyde oxidase (AO) and other enzyme staining patterns (Sprey et al. 1982), E1C antigen localization in a narrow band along the margin (Piovant and Lena 1988). To test our hypothesis that such parameters, and others, act in concert to determine margin identity and the positional information that specifies the bristles and hairs appropriate to the anterior, posterior and distal margins, we have examined these parameters in the dominant mutant Lyra, in which much of the anterior and posterior margins is missing. After establishing that Lyra phenotype is already evident in the early pupal wing, we tested the known imaginal disc parameters and found that only Mab E1C (Piovant and Lena 1988) distribution differs from wild type, suggesting that E1C antigen may be a component of positional information. Sibatani's (1983) model for specification of positional information (PI) applied to wing discs predicts the Lyra adult wing shape as well as the reduced distribution of E1C antigen in Lyra wing discs. The model is based on the assumption that specification of positional information depends on interactions of multiple, independent factors. Clonal analysis with shaggy (Simpson et al. 1988 and Ripoll et al. 1988) indicates that factors in addition to E1C antigen contribute to margin PI in Lyra wings and should allow us to test the multi-component hypothesis further.