Different requirements for l(1) giant in two embryonic domains of Drosophila melanogaster

l(1) giant is a zygotic lethal mutation which affects the embryonic development of both the labial/thoracic segments and a subset of posterior abdominal segments. Using antibodies specific for proteins encoded by several Drosophila genes to identify the compartmental origin of the defects, we show that the requirement of giant activity is different in these two embryonic domains. Anteriorly, the posterior compartment of the labial segment is missing at the blastoderm stage. Posteriorly, cells are specifically deleted by cell death within the anterior compartments of abdominal segments 5-7 during germ band elongation. In mature embryos, posterior compartment structures of the peripheral nervous system of A5-7 are fused. In addition to a different pattern of defect in the two parts of the embryo, the kind of action appears different. Anteriorly, giant resembles a gap mutation in that a particular region is missing from the blastoderm fate map, whereas in the abdominal domain, giant affects the development of anterior compartment-specific structures.     

Different requirements for l(1)giant in two embryonic domains of Drosophila melanogaster

L(1)giant is a zygotic lethal mutation which affects the embryonic development of both the labial/thoracic segments and a subset of posterior abdominal segments. Using antibodies specific for proteins encoded by several Drosophila genes to identify the compartmental origin of the defects, we show that the requirement of giant activity is different in these two embryonic domains. Anteriorly, the posterior compartment of the labial segment is missing at the blastoderm stage. Posteriorly, cells are specifically deleted by cell death within the anterior compartments of abdominal segments 5–7 during germ band elongation. In mature embryos, posterior compartment structures of the peripheral nervous system of A5–7 are fused. In addition to a different pattern of defect in the two parts of the embryo, the kind of action appears different. Anteriorly, giant resembles a gap mutation in that a particular region is missing from the blastoderm fate map, whereas in the abdominal domain, giant affects the development of anterior compartment-specific structures.     

Graded requirement for the zygotic terminal gene, tailless, in the brain and tail region of the Drosophila embryo

We have used hypomorphic and null tailless (tll) alleles to carry out a detailed analysis of the effects of the lack of tll gene activity on anterior and posterior regions of the embryo. The arrangement of tll alleles into a continuous series clarifies the relationship between the anterior and posterior functions of the tll gene and indicates that there is a graded sensitivity of anterior and posterior structures to a decrease in tll gene activity. With the deletion of both anterior and posterior pattern domains in tll null embryos, there is a poleward expansion of the remaining pattern. Using anti-horseradish peroxidase staining, we show that the formation of the embryonic brain requires tll. A phenotypic and genetic study of other pattern mutants places the tll gene within the hierarchy of maternal and zygotic genes required for the formation of the normal body pattern. Analysis of mutants doubly deficient in tll and maternal terminal genes is consistent with the idea that these genes act together in a common pathway to establish the domains at opposite ends of the embryo. We propose that tll establishes anterior and posterior subdomains (acron and tail regions, respectively) within the larger pattern regions affected by the maternal terminal genes.     

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.     

Homoeosis in Drosophila: anterior and posterior transformations of Polycomb lethal embryos

Lethal embryos homozygous for Polycomb (Pc) mutations show transformations of segment-specific cuticular features to those of more anterior or posterior segments; the frequency and extent of such changes show differences which depend on the genotype and the region. The mesothorax of Polycomb lethal embryos often shows posterior transformations of the anterior- and posterior-most portions of the segment, and anterior transformations of the medial portion. A comparison of Polycomb embryos also bearing various genetic lesions of the bithorax gene complex (BX-C) shows that the penetrance of anterior transformation and the extent of posterior transformation in the appears independent of posterior transformation, even though cells undergoing each of these changes lie in close proximity in the developing embryo. It has been shown previously that in Polycomb lethal embryos posterior transformations require the normal function of the BX-C. We show here that anterior transformations of the mesothorax and other segments require the normal function of the Sex combs reduced (Scr) locus, also necessary for the normal development of the prothorax and some head segments. Similar observations are also presented for a Polycomblike mutation. We suggest that in Polycomb embryos there are errors in the clonal transmission of determined states resulting in expression of the BX-C and Scr+ loci at abnormal locations, and that such events are probabilistic in nature and show marked regional differences in frequency.     

Pattern formation in fragmented eggs of the short germ insect Schistocerca gregaria

Summary The effect of transverse fragmentation on the segment pattern of the short germ embryo of the locust Schistocerca gregaria has been investigated at two stages subsequent to the formation of the germ anlage. Following fragmentation both anterior and posterior partial embryos were observed, although rarely in a single egg. Anterior partial patterns usually terminated with a segment visible at the time of fragmentation or with the next segment due to appear. Posterior partial patterns began with a wide range of segments depending on the level of fragmentation.Anterior and posterior partial patterns developing in a single egg were usually not complementary and the segments missing sometimes included some segments visible when the embryo was fragmented. Non-complementary patterns resulted following fragmentation in all regions, while complementary patterns only occurred after fragmentation in the visibly-segmented region.The results suggest that following fragmentation isolated posterior portions of the embryo continue to form segments, while isolated anterior regions usually do not. This effect could result from variable damage to an existing pattern of unequally-sized segment primordia, or from the disruption of a process of sequential segmentation in the elongating posterior region of the embryo. The results are broadly compatible with the progress zone model proposed by Summerbell et al. (1973).     

The in vitro maintenance of the apical ectodermal ridge of the chick embryo wing bud: an assay for polarizing activity.

We have devised an in vitro bioassay for limb bud polarizing activity in the chick embryo. This assay has proven to be a relatively quick and effective test for a morphogenetic factor asymmetrically distributed in the limb bud which is capable of maintaining or thickening the apical ectodermal ridge.A small section of the preaxial border of the chick embryo wing bud was cultured alone, with tissue from the posterior border, mid-dorsal or anterior corner of a second donor wing, or from the flank. The tissue from the preaxial border (responding tissue) consisted of mesoderm with overlying ectoderm and apical ectodermal ridge. When the responding tissue was cultured alone, with flank, or with anterior corner limb tissue, the apical ectodermal ridge flattened in 24–36 hr and many macrophages appeared in the underlying mesoderm. When cultured with posterior border limb tissue however, the apical ridge of the responding tissue remained thickened for up to 48 hr., and no macrophages appear in the underlying mesoderm. The behavior of responding tissue was intermediate between these two extremes when cultured with mid-dorsal limb tissue. The morphogenetic activity assayed by this procedure thus seems to be present as a gradient in the wing bud, with activity decreasing from posterior to anterior. Contact with the responding tissue is not required to enable posterior border tissue to elicit ridge thickening and inhibit the cell death.     

Embryonic development of the alimentary canal and ectodermal derivatives in the primitive moth,Neomicropteryx nipponensis issiki (Lepidoptera,Micropterygidae)

The formation of the alimentary canal, nervous system, and of other ectodermal derivatives in the embryo of the primitive moth, Neomicropteryx nipponensis Issiki, is described. The stomodaeum is formed from an invagination in the medioposterior portion of the protocephalon. The proctodaeum arises as an extension of the amnioproctodaeal cavity. The midgut epithelium orginates from anterior and posterior rudiments in blind ends of the stomodaeum and proctodaeum. The decondary dorsal organ is formed in developing midgut. The development of the brain is typical of insects. The ventral nerve cord originates in large part from neuroblasts arising in 3 gnathal, 3 thoracic, and 11 abdominal segments. Intrasegmental median cord cells probably differentiate into both ganglion cells and glial elements of the ventral nerve cord; intersegmental cells appear not to participate in the formation of the nervous system. The stomatogastric nervous system develops from three evaginations in the dorsal wall of the stomodaeum, and consists of the frontal, hypocerebral, and ventricular ganglia, the recurrent nerve, and corpora cardiaca. Five stemmata arise from the epidermis on each side of the head. Five pairs of ectodermal invaginations are formed in the cephalognathal region to produce the tentorium, mandibular apodemes, corpora allata, and silk glands. Prothoracic glands orginate in the prothorax. Mesothoracic spiracles shift anteriorly to the prothorax during development. Oenocytes arise in the first seven abdominal segments. Invaginated pleuropodia are formed in the first abdominal segment.     

Analysis of cytoplasmic activity dependent on the Drosophila terminal pattern gene torso

Cytoplasm from wildtype Drosophila embryos was transplanted into torso (tor) mutant embryos to determine the distribution of terminal rescuing activity at the cleavage stage. Although posterior and lateral wildtype cytoplasm contained rescuing activity that restored posterior terminal (telson) structures Klingler et al. (1988, Nature (London) 335, 275-277) this rescuing activity was not found in anterior cytoplasm. Similarly, transplantation of anterior and lateral wildtype cytoplasm into the anterior of tor embryos rescued anterior terminal (acron) structures, whereas posterior cytoplasm did not. This failure of reciprocal rescue is due to the presence of the products of the anterior and posterior classes of genes, because anterior cytoplasm from bicoid mutant embryos restored the telson in the posterior as well as the acron in the anterior of tor embryos, and because posterior cytoplasm from nanos embryos rescued the acron in the anterior as well as the telson in the posterior of tor embryos. Therefore terminal rescuing activity is evenly distributed throughout the cleavage stage embryo as anticipated from molecular studies.     

Modulation of zebrafish pitx3 expression in the primordia of the pituitary, lens, olfactory epithelium and cranial ganglia by hedgehog and nodal signaling

In this article we report the isolation of a novel zebrafish gene, pitx3, which plays an important role in the formation of several placode-derived structures. In wildtype embryos, pitx3 is first expressed in a crescent-shaped area in the anterior end of the embryo. At later stages, the primordia of the anterior pituitary, the lens, the olfactory sensory epithelium, and cranial ganglia express this gene. Pitx3 is not expressed in the more posterior preplacodal region that gives rise to the epibranchial, otic, and lateral line placodes. The dynamics of pitx3 in the anterior region of wildtype embryos suggests that pitx3 expression marks a common step in the formation of the pituitary, lens, olfactory placode as well as the trigeminal placode. Analysis of pitx3 expression in mutants lacking the hedgehog or nodal function demonstrates the differential dependence of pitx3 expression in these structures on nodal and hedgehog signaling. While the lens and trigeminal placodes express pitx3 in the absence of hedgehog and nodal signaling, there is no expression of pitx3 in the anteriormost ectoderm adjacent to the neural plate from which the anterior pituitary would derive. In mutants with impaired hedgehog signaling, the lens placode frequently extends into more anterior ventral regions of the embryo.     

Developmental analysis of the torso-like phenotype in Drosophila produced by a maternal-effect locus

The segmental plan of the Drosophila embryo is already established at the blastoderm stage through the action of maternal effect genes which determine the polarity of the embryo and zygotically active genes involved in segmentation. We have analyzed the first example of a group of maternally acting genes which are necessary for establishing the developmental potential of the posterior 25% of the blastoderm. Females, homozygous for the X-linked maternal-effect mutation female sterile(1)Nasrat211 [fs(1)N211], produce embryos, characterized as torso-like, which lack all posterior endodermal derivatives as well as structures characteristic of abdominal segments 8 to 10. In addition, anterior endodermal derivatives are deficient and the absence of pharyngeal musculature causes a collapse of the cephalopharyngeal apparatus. The columnar blastoderm cell layer is defective at the posterior tip below the pole cells in these embryos. This defect, however, is presumably secondary to some abnormal feature of pole cell formation since in double mutants of fs(1)Nasrat211; tudor3 the blastoderm is normal but the embryos still show the torso-like phenotype. In situ hybridization with RNA probes derived from the fushi tarazu gene establishes that the cellular determination of the posterior blastoderm of embryos produced by fs(1)N211 is changed. This represents the first direct demonstration that a maternal-effect mutation alters the spatial distribution of a zygotic gene product involved in the segmental patterning of the embryo.     

hunchback, a gene required for segmentation of an anterior and posterior region of the Drosophila embryo

The locus hunchback (hb) is a member of the gap class of segmentation genes of Drosophila. A number of X-ray-induced deletions locate the hb locus at the chromosomal site 85A3-B1, to the right of the pink locus, which maps in the same interval. A total of 14 EMS and 3 X-ray-induced hb alleles have been studied. Homozygous mutant embryos show deletions of segments in two separate regions. In the six strong alleles, the labium and all three thoracic segments are deleted anteriorly while posteriorly the 8th abdominal segment and adjacent parts of the 7th abdominal segment are lacking. The eight weak alleles show smaller deletions both in the thoracic and posterior abdominal region. In the weakest allele only part of the mesothorax is deleted. Three hb alleles produce a homoeotic transformation: superimposed on a strong or weak deletion phenotype, head or thoracic segments are transformed into abdominal segments, respectively. This suggests that hb might also be involved in the regulation of genes in the Bithorax complex (BX-C). Fate mapping of the normal-appearing segments in strong mutant embryos using the UV-laser beam ablation technique (Lohs-Schardin et al., 1979) shows that these segments arise from the normal blastoderm regions. The mutant phenotype can be recognized soon after the onset of gastrulation in a failure to fully extend the germ band. In 6-hr-old mutant embryos, two clusters of dead cells are observed in the thoracic and posterior abdominal region. These observations indicate region specific requirement of hb gene function. The analysis of germ line chimeras by transplantation of homozygous mutant pole cells shows that hb is already expressed during oogenesis. Homozygous mutant embryos derived from a homozygous mutant germ line have a novel phenotype. The anterior affected region is enlarged, including all three gnathal segments and the anterior three abdominal segments. In addition three abdominal segments with reversed polarity are formed between the remaining head structures and the posterior abdomen. Heterozygous mutant embryos derived from a homozygous mutant germ line develop normally, indicating that maternal gene expression is not required for normal development.     

Control and function of terminal gap gene activity in the posterior pole region of the Drosophila embryo.

We have studied the genetic requirement for the normal expression of the terminal gap genes huckebein (hkb) and tailless (tll) and their possible function in the posterior pole region of the Drosophila embryo. At the early blastoderm stage, both genes are expressed in largely coextensive expression domains. Our results show that in the posterior region of the embryo both the activation and the control of the spatial limits of tll and hkb expression are critically dependent on torso (tor) activity, which is thought to be a crucial component of a cellular signal transduction pathway provided by the terminal maternal system. Furthermore, the spatial control of hkb and tll expression does not require mutual interactions among each other, nor does it require regulatory input from other gap genes which are essential for the establishment of segmentation in the trunk region of the embryo ("central gap genes"). Therefore, the terminal gap genes have unique regulatory features which are distinct from the central gap genes. In the absence of terminal gap gene activities, as in hkb and tll mutant embryos, the expression domains of the central gap genes expand posteriorly, indicating that the terminal gap gene activities prevent central gap gene expression in the posterior pole region of the wildtype embryo. This, in turn, suggests that the terminal gap gene activities prevent metamerization by repression of central gap genes, thereby distinguishing the segmented trunk from the nonsegmented tail region of the embryo.     

三种蚤生殖系统的细微结构:雌性外生殖器的发育

本文研究了缓慢细蚤 Leptopsylla segnis(Schōnherr),不等单蚤 Monopsyllus anisus(Rothschild)和猫栉首蚤指名亚种Ctenocephalides felis felis(Bouché)雌性外生殖器的结构,观察了从幼虫、前蛹、蛹至成虫各发育时期的雌性外生殖器的内部结构变化.对一直悬而未决的雌蚤中输卵管等的起源问题,进行了详细的观察和探讨.认为从晚期3龄幼虫开始出现的雌性外生殖器芽,在前蛹期成为四个部分:1.第7腹板后缘腹壁内陷形成的一对外胚层囊;2.紧接外胚层囊后并延伸至第8腹板的外胚层增厚;3.在第8腹板后部,外胚层增厚两侧的产卵器芽;4.第8腹板后缘腹壁内陷形成的受精囊芽.并认为,这三种蚤的中输卵管由一对外胚层囊和其后的外胚层增厚前端的一小部分内陷形成,阴道由外胚层增厚的大部分和第8、9腹板腹壁内陷形成,受精囊由受精囊芽内陷形成.     

Genetic analysis of pattern-formation in the embryo ofDrosophila melanogaster

Summary The mutationbicaudal (Bull, 1966) causes embryos to develop a longitudinal mirror image duplication of the posteriormost abdominal segments, while head and thorax are missing. These embryos occur with varying frequencies among eggs laid by mutant females, irrespective of the paternal genotype. Recombination and deletion mapping indicate thatbicaudal (bic) is a recessive, hypomorphic, maternal-effect mutation mapping at a single locus on the second chromosome ofDrosophila melanogaster close tovg (67.0±0.1). The frequency of bicaudal embryos depends on the age of the mother, her genetic constitution and the temperature at which she is raised. Best producers are very young females hemizygous forbic (bic/Df(2)vg ^B ) at 28° C. Under these conditions 80% to 90% of the eggs which differentiate can show the bicaudal embryo phenotype. Upon ageing of the mother the frequency of bicaudal embryos declines rapidly, and most of the eggs develop the normal body pattern. Temperature shift experiments suggest a temperature-sensitive period at the onset of vitellogenesis.The mutation causes several types of abnormalities in the segment pattern of theDrosophila embryo, which are interpreted as various degrees of expression of the mutant character. The most frequent abnormal phenotype is the symmetrical bicaudal embryo with one to five abdominal segments duplicated. Less frequent are asymmetrical types, in which the smaller number of segments is always in the anterior reversed part. Other phenotypes are embryos with missing or rudimentary heads, and embryos with irregular gaps in the segment pattern. In bicaudal embryos, the pole cells, formed at the posterior pole of the egg prior to blastoderm formation, are not duplicated at the anterior. The significance of thebicaudal phenotypes for embryonic pattern-formation inDrosophila is discussed.     

A scanning electron microscope study of the developing embryo of Manduca sexta (L.) (Lepidoptera : Sphingidae)

Scanning electron microscopy of the developing Manduca sexta (Lepidoptera : Sphingidae) embryo reveals that the body wall of the insect undergoes considerable morphogenesis beginning at 20 hr post-oviposition. The elongated 19 hr embryo contracts in length, which gives rise to the formation of rudimentary segments. By 33 hr, many of the appendage anlagen are visible, the presumptive spiracles appear as bifurcate pits and the proctodeum begins invagination. During this same period, prior to katatrepsis, the body walls become established, and the segments and appendages develop. Between 50 and 60 hr post-oviposition, involution of the oral cavity and reorientation of the associated gnathal appendages occurs. During this same period, katatrepsis and provisional dorsal closure take place. Developmental polarity is evident as a distinctive wave of specialization proceeding posterior to anterior in the thorax/abdomen, and anterior to posterior in the head. Configuration of the oral cavity is strikingly prognathous until just prior to eclosion. Two embryonic molts are apparent, as determined by the remnants of ecdysed “embryonic cuticles”.     

Homoeotic Gene ETc Controls the Cell Number of Embryonic Ectodermal Layers of Bombyx mori

The formation of segments of Bombyx larvae involves differentiation of legged and legless segments during embryogenesis. Observations by light microscopy of serial sections of developing embryos of Bombyx showed that the cell number of the ectodermal layers increased more rapidly in segments where legs were being extruded than in those where no appendages were formed. In the embryos of a homoeotic mutant for the E -pseudoallelic locus (about 0.0–VI), E^Tc/E^Tc , in which all the abdominal segments were legless, the cell number of the ectodermal layers did not increase as in normal embryos. These findings suggest that the E^Tc gene controls the cell number of the ectodermal layers in relation to the differentiation of abdominal segments.     

l(1)pole hole is required maternally for pattern formation in the terminal regions of the embryo

Maternal expression of the l(1)pole hole (l(1)ph) gene product is required for the development of the Drosophila embryo. When maternal l(1)ph+ activity is absent, alterations in the embryonic fate map occur as visualized by the expression of segmentation genes fushitarazu and engrailed. If both maternal and zygotic activity is absent, embryos degenerate around 7 h of development. If only maternal activity is missing, embryos complete embryogenesis and show deletions of both anterior and posterior structures. Anteriorly, structures originating from labral and acron head regions are missing. Posteriorly, abdominal segments A8, 9 and 10, the telson and the proctodeum are missing. Similar pattern deletions are observed in embryos derived from the terminal class of female sterile mutations. Thus, the maternal l(1)ph+ gene product is required for the establishment of cell identities at the anterior and posterior poles of the Drosophila embryo.