Pattern formation in the egg of the leafhopper Euscelis plebejus Fall. (Homoptera): Developmental capacities of fragments isolated from the polar egg regions

The egg of the leafhopper Euscelis plebejus has been separated into three fragments [for nomenclature, see Sander, K. (1976). Advan. Insect Physiol.12, 125–238] by two constrictions in order to exclude the middle egg part from possible terminal influences on pattern specification. Middle fragments of freshly laid eggs (two pronuclei or one nucleus) differentiate middle segments of the embryonic pattern. The segment composition of those partial patterns varies with the position of the two constrictions. Eggs subdivided at later stages of development produce similar partial patterns in the middle fragment, but with more segments. The mode of segment expression in single and double fragmented eggs is compatible with the assumption that the metameric pattern is differentiated by a sequence of short-range inductions rather than by an extensive gradient field.     

Regionalisation of segment-forming capacities during early embryogenesis inDrosophila melanogaster

Summary Transverse fragmentation of the egg ofDrosophila melanogaster results in the formation of partial larvae. Anterior and posterior egg fragments develop the respective partial larval patterns. The partial patterns do not add up to the complete pattern.Fragmentation near the middle of the egg during early cleavage causes a gap of 3–4 segments on average in the larva. This gap is reduced to 2 segments on average if operations are performed at the early syncytial blastoderm stage. Fragmentation near the pole regions from early cleavage stages onwards causes a gap of only 2 larval segments on average. When the egg is fragmented at the columnar cellular blastoderm stage or later, the gap at all positions amounts to the size of one segment or less. A gap is also found after incomplete fragmentation, when the ooplasmic bridge between both egg parts was constricted beyond a certain limit.A specific shift of the segment-forming capacities along the egg axis is observed from syncytial blastoderm stages onwards.After partial longitudinal fragmentation no additional structures are observed. In general, the partial transverse patterns add up to the complete pattern, but minor structures like single denticles are missing near the fragmentation site.The results are discussed with respect to current concepts of segment pattern formation during early embryogenesis in dipterans.     

Development of the embryonic segment pattern in the pea-beetle Callosobruchus maculatus. Supracellular,cellular and molecular aspects

Summary

This review deals with the question of how cells in the early embryo of the pea-beetle differentiate into a sequential pattern of segments. Anterior and posterior fragments of an egg have different options for development depending on whether they are exposed, before cellularization, to decaying ooplasm in the complementary fragment. Without such exposure all fragments produce fewer segments than corresponding fragments obtained at cellularization. With exposure a fraction of anterior and posterior fragments produces considerably more segments than corresponding fragments obtained at cellularization. In addition, posterior fragments are uniquely different from anterior ones in that they also produce reversal of segment sequence which can be restricted to longitudinal strips of the larval cuticle.

The difference in reaction to decaying ooplasm between anterior and posterior fragments suggests an asymmetry in the control of metamerization. Lateral inhibition by an asymmetric gradient of a diffusible morphogen can describe these observations [18] except for the restriction of reversal to longitudinal strips. The latter requires either that morphogen transport be polarized, possibly by a voltage gradient in the egg, or that the interpretation of cell position is polarized. The induction of double abdomens with UV-light and RNase suggests that RNA is part of the control mechanism. This and strip-restricted reversal are features shared by eggs of Coleoptera and Diptera.     

Parameters influencing reversal of segment sequence in posterior egg fragments ofCallosobruchus (Coleoptera)

Summary The double abdomen type of embryonic segment pattern can develop in posterior fragments ofCallosobruchus eggs. In this type of pattern, a series of posterior segments is joined in reversed polarity to an equal set from the original pattern persisting in normal polarity. Reversed and non-reversed sets are fused in a plane of mirror symmetry, which shows in the larval cuticle as a symmetry line. This line may be located anywhere in the posterior thorax or the anterior abdomen. The reversed abdomen may be incomplete caudally due to secondary causes. Polarity reversal and concomitant double abdomen formation occurred only when temporary constriction was terminated before cellularization of the blastoderm, and only when the anterior fragment was degenerating. Maximum reversal frequency was 94% of analyzable posterior partial larvae when the constriction was applied slightly anterior to the middle of the egg when the egg contained 4–32 nuclei. Reversal was often restricted to longitudinal strips of the larval cuticle. The longitudinal borderlines between the reversed and the non-reversed strips ran predominantly along the larval midlines. Such borderlines probably existed in the blastoderm anywhere around its circumference, but borderlines in the future mesoderm and serosa would be internalized during gastrulation and dorsal closure, respectively, and the embryonic midlines would then become secondary borderlines visible in the larval cuticle. If a morphogen is involved in segment pattern formation, its transport in the egg must be polarized longitudinally in order to account for reversals restricted to longitudinal cuticular strips.     

The specification of metameric order in the insectCallosobruchus maculatus Fabr. (Coleoptera)

Summary Mechanically dividing an insect egg into anterior and posterior fragments results in a segment gap (Sander 1976), a loss of non-terminal segments in the constricted region. By altering the stage and duration of constriction, we produced different types of egg fragments in the pea beetleCallosobruchus. The patterns formed by these fragments suggest the existence of interactions between anterior and posterior egg regions that influence segment patterning and placement. Segments in excess of the numbers expected on the basis of permanent constrictions were produced in fragments when: (1) the constriction was released before cellularization occurred and (2) in addition the complementary fragment degenerated. Apparently the degenerating fragment induced the formation of excess segments in the developing fragment. Differences in the time and extent of excess segment formation in anterior versus posterior fragments suggest an asymmetric distribution of prerequisites for segment formation. This conclusion is consistent with our finding that a partial reversal of segment sequence (double abdomen formation) can be induced only in posterior fragments by a degenerating fragment, but not in anterior fragments (see companion paper).The formation of excess segments shows that the segment gap observed after permanent separation cannot be due to non-specific damage, caused by the process of constriction as such, to the egg or to localized putative segment precursors.     

Localized synthesis of specific proteins during oogenesis and early embryogenesis inDrosophila melanogaster

Summary Protein synthesis in egg follicles and blastoderm embryos ofDrosophila melanogaster has been studied by means of two-dimensional gel electrophoresis. Up to 400 polypeptide spots have been resolved on autoradiographs. Stage 10 follicles (for stages see King, 1970) were labelled in vitro for 10 to 60 min with³⁵S-methionine and cut with tungsten needles into an anterior fragment containing the nurse cells and a posterior fragment containing the oocyte and follicle cells. The nurse cells were found to synthesize a complex pattern of proteins. At least two proteins were detected only in nurse cells but not in the oocyte even after a one hour labelling period. Nurse cells isolated from stages 9, 10 and 12 follicles were shown to synthesize stage specific patterns of proteins. Several proteins are synthesized in posterior fragments of stage 10 follicles but not in anterior fragments. These proteins are only found in follicle cells. No oocyte specific proteins have been detected. Striking differences between the protein patterns of anterior and posterior fragments persist until the nurse cells degenerate. In mature stage 14 follicles, labelled in vivo, no significant differences in the protein patterns of isolated anterior and posterior fragments could be detected; this may be due to technical limitations. At the blastoderm stage localized synthesis of specific proteins becomes detectable again. When blastoderm embryos, labelled in vivo, are cut with tungsten needles and the cells are isolated from anterior and posterior halves, differences become apparent. The pole cells located at the posterior pole are highly active in protein synthesis and contribute several specific proteins which are found exclusively in the posterior region of the embryo. In this study synthesis of specific proteins could only be demonstrated at those developmental stages which are characterized by the presence of different cell types within the egg chamber, while no differences were detected when stage 14 follicles were cut and anterior and posterior fragments analyzed separately. The differences in the pattern of protein synthesis by pole cells and blastoderm cells indicate that even the earliest stages of determination are reflected by marked changes at the biochemical level.     

Spermatogenesis in pharate adult testes of Drosophila in tissue cultures without ecdysones

The process of spermatogenesis in explanted testicular fragments from pharate adults (48 hr after puparium formation) of Drosophila melanogaster was examined under in vitro conditions without any added ecdysone substances. In the anterior fragments, which contained spermatogonia, no or only slight changes were found. In the middle fragments which contained germ cells at more advanced stages of spermatogenesis, spermatocytes, and spermatids, a slight increase in the number of spermatocytes or spermatids was observed. In the posterior fragments, which contained sperms at early stages of spermiogenesis, there was a marked elongation of the sperm bundles along their long axis.     

L'oeuf de Myrmeleotettix maculatus Thunb. (Orthoptera : Acrididae): Absorption d'eau et structure fine des enveloppes

Water absorption and fine structure of the egg shell have been studied in the eggs of Myrmeleotettix maculatus (Orthoptera : Acrididae). At the anterior pole of these eggs, there is a respiratory plastron and at the posterior end, behind the ring of micropyles, many minute holes can be seen. Eggs of M. maculatus incubated on wet filter paper at 30°C absorb water before diapause between the 5th and the 25th day after oviposition. The period of water absorption coincides with the serosal cuticle secretion. The increase in volume of the egg does not seem to involve any fragmentation in the chorion. The chorion is composed of 3 layers (upper, middle and lower). The middle layer, the thickest one, contains twisted elements with a paracrystalline structure. During the first days of incubation, the vitelline membrane becomes changed. In the newly laid egg, it is granular and homogeneous. Five days later, 4 layers with different structures can be distinguished. After 30 days, the serosal cuticle presents a thin epicuticule and a thick lamellated endocuticule with many pore canals.     

Proteins foretelling head or abdomen development in the embryo of Smittia spec. (Chironomidae,Diptera)

The development of the segment pattern in Smittia embryos can be manipulated experimentally. Centrifugation during intravitelline cleavage leads to a mirror image duplication of most of the head in the absence of abdominal segments (“double cephalons”). Conversely, mirror image duplications of abdominal segments in the absence of head and thorax (“double abdomens”) can be generated by UV-irradiation of the anterior pole before blastoderm formation. By subsequent exposure to blue light, UV-irradiated embryos can be reprogrammed for normal development (photoreversal). We have characterized an “anterior indicator” protein (designated AI₁; M_r ? 35,000; IEP ? 4.9). Its synthesis was restricted to anterior fragments of embryos during a late blastoderm stage (Bl_VI). This protein was synthesized, however, in both anterior and posterior fragments of prospective double cephalons. Conversely, this protein was synthesized neither in anterior nor in posterior fragments of UV-induced double abdomens. Upon photoreversal, the protein was synthesized again in anterior fragments. Thus, synthesis of this protein in a given fragment always indicated development of head and thorax there. Likewise, we have characterized a “posterior indicator protein” (designated PI₁, M_r ? 50,000, IEP ? 5.5). Its synthesis during early blastoderm stages (Bl_I and Bl_II) was restricted to posterior fragments but not to pole cells in normal embryos. In UV-induced double abdomens, PI_I was synthesized in both anterior and posterior fragments at stage Bl_II. Photoreversal again led to restriction of PI_I synthesis to posterior fragments. Thus, the synthesis of PI_I in a given fragment at stage Bl_II always foreshadowed the formation of an abdomen several hours before this can be discerned morphologically. The synthesis of two other proteins (designated a₁ and p₁) was also restricted, during certain blastoderm stages, to anterior or posterior fragments, respectively. However, UV-irradiation or centrifugation had little or no effect on the synthesis of these proteins. Conversely, programming embryos for double abdomen development by UV-irradiation caused a set of reproducible, and mostly photoreversible, changes in the pattern of proteins synthesized in anterior embryonic fragments. However, the synthesis of most of the affected proteins was not region-specific in normal embryos.     

Morphology of the egg shell and the developing embryo of the Red Palm Weevil,Rhynchophorus ferrugineus (Oliver)

The harvested eggs of Rhynchophorus ferrugineus are ovo-cylindrical shaped, averaged 1.09 mm in length and 0.43 mm in width, with ratio of L\W 4.42. The chorionic layer of electron dense material is seen covering the exochorion structure of the eggs. The egg main body chorion exhibits a polygonal pattern and architecture surface of the egg is supported by a system of irregular interconnecting grooves. The micropylar apparatus of the eggs of the Red Palm Weevil, R. ferrugineus is described in the present study for the first time. Two micropylar openings are found closed to the center of the posterior wide pole of the egg. Each micropylar opening presents a single small orifice and its surrounding chorion is porous and densely set with tiny projections allowing the spermatozoa to penetrate the egg. Respiratory aeropyles are distributed on the borders of reticulations in the area chorionic surface of egg capsule. The hatching region is detected on the anterior part at the opposite side of the egg. Changes in the appearance and shape of R. ferrugineus eggs as well as the incidence of embryonic development are observed.     

Expression of <Emphasis Type="Italic">hunchback</Emphasis> during oogenesis and embryogenesis in <Emphasis Type="Italic">Locusta migratoria manilensis</Emphasis> (Meyen)

hb (hunchback) is a contributing factor in anteroposterior axial patterning of insects. Although the hb function in Locusta migratoria manilensis has been investigated, its expression pattern remains unknown. Here, the mouse polyclonal antibody was produced against Hb fusion protein, and then its expression pattern during oogenesis and embryogenesis of L. migratoria manilensis was examined by immunohistochemical staining. Hb protein was detected in the oocyte nucleus which was positioned centrally within the developing oocyte. The oocyte nucleus gradually moved to the posterior end of the egg along with the oocyte maturing. In freshly laid eggs, Hb formed gradient at the posterior end of the egg, and then hb was expressed as a band in the middle of the blastodisc. As the blastodisc differentiated into the head and trunk, the expression region became wide, which would develop into spatial gnathal and thoracic segments. With abdominal segmentation, the expression domain in the gnathal and thoracic region became faint and eventually faded out, while the Hb expression domain appeared at the posterior growth zone in a discontinuous expression manner. The hb expression pattern of L. migratoria manilensis is greatly similar to that of other locusts, such as Schistocerca americana and another L. migratoria. Compared with other insects, hb expression is conserved in the gnathal and thoracic domains, while divergent in oogenesis and abdomen.     

Endosymbionts: factors on egg pattern formation

Elimination of the intracellular symbionts of Euscelis plebejus either by X-ray irradiation of the posterior pole of the freshly laid egg or by interruption of egg infection by application of tetracycline or lysozyme to female leafhoppers leads to the production of embryos without abdomens, ‘head-embryos’.Homogenates of symbiont-free eggs and symbiont-containing eggs in the state of invagination have a pH of 7·5±0·2 and 7·0±0·2 and an osmotic pressure (pO) of 8·3±0·2 and 7·8±0·2, respectively. The presence of symbionts leads to a decrease of both the pH and pO.These data indicate that the correct formation of the posterior gradient, necessary for normal abdomen development, is dependent on the presence of endosymbionts at the posterior pole. It is possible that the symbionts change the pH and pO of the posterior gradient. These results are consistent with a hypothetical model of early differentiation of the Euscelis egg.     

A Chemical and Physical Characterization of Echinoid RNA during Early Embryogenesis

The properties of the major RNA components prepared from Arbacia punctulata have been characterized by sedimentation in sucrose gradients and analysis of base composition. Comparison of the components found in the unfertilized egg with those observed subsequent to fertilization revealed no differences in any of the embryonic stages examined. The base composition and sedimentation profiles of RNA from unfertilized nuclear egg fragments and from 105,000 g pellet were similar to those of the intact egg. It is concluded that the early stages of embryogenesis are not accompanied by detectable alteration of the physical or chemical characteristics of the major RNA components found in the unfertilized egg.     

Recovery and Longevity of Egg Masses of Meloidogyne incognita during Simulated Winter Survival

Effects of soil matrix potential on longevity of egg masses of Meloidogyne incognita were determined during simulated winter conditions. Egg masses were recovered from isolated root fragments incubated in field soil at matrix potentials of -0.1, -0.3, -1.0, and -4.0 bars throughout winter survival periods of 10 weeks for tomato roots and 12 weeks for cotton roots. Egg masses were more superficial on cotton roots than on tomato roots and were more easily dislodged from cotton roots during recovery of root fragments by elutriation. The rate of decline in numbers of eggs and J2 per egg mass was greater in wet as compared to dry soils (P = 0.01), with the relationship between numbers of eggs and J2 per egg mass and time being best described by quadratic models. Percentage hatch of recovered eggs declines linearly with time at soil matrix potentials of -0.1 and -0.3 bars, but at -1.0 and -4.0 bars the percentage hatch of recovered eggs increased before declining. Effects of soil matrix potential on numbers of eggs per egg mass and percentage hatch of recovered eggs were consistent with previous reports that low soil moisture inhibits egg hatch before affecting egg development. Estimations of egg population densities during winter survival periods will be affected by ability to recover infected root fragments from the soil without dislodging associated egg masses. There is a need for procedures for extraction of egg masses not attached to roots from the soil.     

Modifying effects of ultraviolet irradiation on the development of abnormal body patterns in centrifuged insect embryos (Smittia sp., Chironomidae,Diptera)

In Smittia and other chironomid embryos, both anterior and posterior egg halves can give rise to either anterior or posterior segments. Upon various types of experimental interference, eggs may develop one of four basic body patterns: normal embryos, double cephalons, double abdomens, or inverted embryos. From a previous model of anteroposterior determination, we derive four sets of predictions for the results of combined ultraviolet irradiation and centrifugation experiments. While most of the actual results are in agreement with the predictions, some are not. Most of the discrepancies are resolved in a modified version of the model. According to the new model, anterior and posterior egg halves contain both anterior and posterior cytoplasmic determinants. These are thought to be mutually repressive, and to control an overall determination for either anterior or posterior development. Centrifugation and ultraviolet irradiation appear to affect the relative strength of anterior determinants in one or both of the egg halves, thus modifying the probabilities for the four basic body patterns to develop. Different frequencies of these patterns, which have been obtained after similar experimental treatment of different chironomid species, can be ascribed to species-specific variation in the ultraviolet sensitivity of anterior and posterior determinants.     

Heterodera glycines Cyst Components and Surface Disinfestants Affect H. glycines Hatching

We investigated the effects of Heterodera glycines cyst components and surface disinfestants on hatching of H. glycines eggs in vitro. Eggs were incubated in either H. glycines cyst wall fragments, cyst wall and egg rinsate, egg homogenate, or control solutions of soybean root diffusate, sterile distilled water, or zinc sulfate. Hatch in cyst wall and egg rinsate, and egg homogenate, was greater (α = 0.05) than hatch in sterile distilled water; however, it was not different from hatch in zinc sulfate according to Dunnett''s test. Hatch in cyst wall fragments was similar to hatch in sterile distilled water. To determine whether surface disinfestants affected hatch, eggs were treated first with chlorhexidine diacetate, mercuric chloride, sodium hypochlorite, or streptomycin sulfate and then incubated in H. glycines egg homogenate, soybean root diffusate, sterile distilled water, or zinc sulfate. Hatch of eggs treated with chlorhexidine diacetate, mercuric chloride, and streptomycin sulfate was reduced (α = 0.05), and hatch of eggs treated with sodium hypochlorite was increased (α = 0.05) relative to hatch of nontreated eggs in all incubation solutions except zinc sulfate according to Dunnett''s Test. Hatch in zinc sulfate was similar among all surface disinfestants except mercuric chloride, where hatch was reduced relative to hatch of nontreated and other surface disinfestant-treated eggs.     

Embryology and Life Cycle of Tylenchorhynchus claytoni Steiner, 1937 (Nematoda: Tylenchoidea)

Development of Tylenchorhynchus claytoni from unsegmented egg to hatching takes 135 hr at 22-25 C. The fourth molt lasts 5 to 6 days. During exsheathment the cast cuticle of the larva separated into two unequal parts, breaking near either the anterior or posterior end. The life cycle from egg to egg required from 31 to 38 days at 28 C on alfalfa seedlings and included four molts and four larval stages. Sexual differentiation was apparent in third-stage larvae.     

Le rôle du système nerveux central sur les mécanismes de l'oviposition chez Carausius morosus et Clitumnus extradentatus

Cephalic nervous connexions were found necessary for oviposition and normal egg maturation in the two species studied. Neurosecretory cells of A type from the brain, suboesophageal, thoracic, and four abdominal ganglia seem to elaborate a stimulating substance for egg laying. This neurosecretion type is not present in corpora cardiaca, corpora allata, the four last abdominal ganglia, or perisympathetic organs which have no clear-cut effect on oviposition. The circadian rhythm of egg laying appears to be entirely controlled by the liberation of this neurosecretion and by an inhibitory factor localized in the head.In Carausius, egg deposition by the valvulae of the ovipositor is regulated by these two factors whereas egg transit through the common oviduct is a distinct preliminary step under nervous control. This nervous effect from the posterior region does not exist in Clitumnus.     

The structure of the egg-shell of Porrocaecum ensicaudatum (Nematoda: Ascaridida)

Wharton D. A. 1979. The structure of the egg-shell of Porrocaecum enslcaudatum (Nematoda: Ascaridida). International Journal for Parasltology9: 127–131. The egg-shell of Porrocaecum ensicaudatum is oval with an opercular plug at either end. The shell consists of three layers: an inner lipid layer, a middle chitinous layer and an outer vitelline layer. The vitelline layer has strands of particulate material attached to its outer surface. The chitinous layer consists of 8.5 nrn fibrils which are made up of a chitin microfibril core surrounded by a protein coat. The fibrils are oriented randomly or in parallel, there being no indication of helicoidal architecture.The chitinous layer varies in thickness to form a pattern of interconnecting ridges on the surface of the egg. This pattern presumably increases the shell's structural strength.