Early Postembryonic Development Research Articles

Digestive tract ontogeny of Dicentrarchus labrax: Implication in osmoregulation

The ontogeny of the digestive tract (DT) and of Na(+)/K(+)-ATPase localization was investigated during the early postembryonic development (from yolk sac larva to juvenile) of the euryhaline teleost Dicentrarchus labrax reared at two salinities: seawater and diluted seawater. Histology, electron microscopy and immunocytochemistry were used to determine the presence and differentiation of ion transporting cells. At hatching, the DT is an undifferentiated straight tube over the yolk sac. At the mouth opening (day 5), it comprises six segments: buccopharynx, esophagus, stomach, anterior intestine, posterior intestine and rectum, well differentiated at the juvenile stage (day 72). The enterocytes displayed ultrastructural features similar to those of mitochondria-rich cells known to be involved in active ion transport. At hatching, ion transporting cells lining the intestine and the rectum exhibited a Na(+)/K(+)-ATPase activity which increased mainly after the larva/juvenile (20 mm) metamorphic transition. The immunofluorescence intensity was dependent upon the stage of development of the gut as well as on the histological configuration of the analyzed segment. The appearance and distribution of enteric ionocytes and the implication of the DT in osmoregulation are discussed.

Development of hypophysis and differentiation of its secretory cells at the early postembryonic development of silver carp Hypophthalmichthys molitrix (cyprinidae)

Silver carp Hypophthalmichthys molitrix hatches from the envelope at phase 19 a day after fecundation (water temperature 26–28°C) with body length 5.2 mm. The formation of hypophysis begins 7–8 h after hatching of the embryo. The first chromophilic cells (acidophiles in adenohypophysis) appear at the age of 9 days; the first basophilic cells (thyrotropocytes) at the age of 17–20 days, when juveniles are at stage III. The gonadotropic function is formed in the ontogenesis of silver carp at the age of 40–45 days, i.e., almost a month after the appearance of elementary sexual cells in the gonads. The differentiation of gonadotropocytes in mesoadenohypophysis to two functionally active types of cells (central and peripheral) is also completed by this time.

Manifestation of heterosis during early maize (Zea mays L.) root development

Heterosis is typically detected in adult hybrid plants as increased yield or vigor compared to their parental inbred lines. Only little is known about the manifestation of heterosis during early postembryonic development. Objective of this study was to identify heterotic traits during early maize root development. Four German inbred lines of the flint (UH002 and UH005) and dent (UH250 and UH301) pool and the 12 reciprocal hybrids generated from these inbred lines were subjected to a morphological and histological analysis during early root development. Primary root length and width were measured daily in a time course between 3 and 7 days after germination (DAG) and displayed average midparent heterosis (MPH) of 17-25% and 1-7%, respectively. Longitudinal size of cortical cells in primary roots was determined 5 DAG and displayed on average 24% MPH thus demonstrating that enlarged primary roots of hybrids can mainly be attributed to elongated cortical cells. The number of seminal roots determined 14 DAG showed on average 18% MPH. Lateral root density of all tested hybrids was determined 5 DAG. This root trait showed the highest degree of heterosis with an average MPH value of 51%. This study demonstrated that heterosis is already manifesting during the very early stages of root development a few days after germination. The young root system is therefore a suitable model for subsequent molecular studies of the early stages of heterosis manifestation during seedling development.

Plasticity of grasshopper vitellogenin production in response to diet is primarily a result of changes in fat body mass

Life history plasticity is the developmental production of different phenotypes by similar genotypes in response to different environments. Plasticity is common in early post-embryonic or adult development. Later in the developmental stage, the transition from developmentally plastic to canalized (i.e., inflexible) phases is often associated with the attainment of a threshold level of storage. Thresholds are often described simply as total body mass or cumulative consumption of food. The physiological characteristics of thresholds, such as the contributions of the growth of particular organs or the production rate of proteins, are largely unstudied. To address the physiology underlying a threshold-induced developmental transition, total vitellogenin production in response to diet quality in the lubber grasshopper was studied. For individuals that differed in age or dietary protein, somatic mass, ovarian mass, fat body mass, mass-specific vitellogenin production, vitellogenin titer, and storage protein titer were measured. Age and diet strongly affected these parameters, with ovarian mass and fat body mass contributing most to the differences. During mid vitellogenesis, females were highly plastic in response to changing food quality. Only during late vitellogenesis were females unresponsive to changes in food quality. Fat body mass was a more important component of plasticity than was mass-specific vitellogenin production. Because these two variables together make up total vitellogenin production, the greater contribution of fat body mass than mass-specific vitellogenin production suggests that growth factors may be more important than tissue stimulators in producing developmental changes in total vitellogenin production. To our knowledge, this is the first study to demonstrate that mass gain of an organ is more important to developmental plasticity than is the output of that same organ.

Effect of Temperature on the Rate of Oxygen Consumption during the Second Half of Embryonic and Early Postembryonic Development of European Pond Turtle Emys orbicularis (Reptilia: Emydidae)

Oxygen consumption by eggs of European pond turtle was determined at two constant incubation temperatures of 25 and 28 degrees C during the second half of embryogenesis. During development at both temperatures, the rate of oxygen consumption initially increased to remain constant during the last quarter of embryogenesis. The difference between the rates of oxygen consumption at these temperatures decreased during the studied period. The coefficient Q10 for the rate of oxygen consumption decreased from 9 to 1.7. At an incubation temperature of 28 degrees C, the changes in the rate of oxygen consumption in response to a short-term temperature decrease to 25 degrees C or increase to 30 degrees C depended on the developmental stage and were most pronounced at the beginning of the studied period. During late embryonic and first 2.5 months of postembryonic development, the rate of oxygen consumption did not significantly differ after such temperature changes. The regulatory mechanisms formed during embryonic development are proposed to maintain the level of oxygen consumption during temperature changes.

Growth and oxygen consumption in embryonic and early postembryonic development of European pond turtle Emys orbicularis (Reptilia: Emydidae)

Experiments on developing eggs of European pond turtle (Emys orbicularis) demonstrated S-shaped changes in the rate of oxygen consumption and body weight during embryonic development. The rate of oxygen consumption and weight progressively increased within 70 days after hatching. During embryogenesis, the rate of oxygen consumption decreased. After hatching, it increased but then decreased to a certain level, which remained constant to the end of the studied period. We observed unidirectional changes in oxygen consumption rate during embryonic period and this pattern was maintained after hatching as well. The coefficients of the allometric relationship between oxygen consumption and body weight were a = 0.33 and k = 0.52 during the embryonic period and a = 0.17 and k = 0.89 during the postembryonic period.

Newborn cells in the adult crayfish brain differentiate into distinct neuronal types

Mitotically active regions persist in the brains of decapod crustaceans throughout their lifetimes, as they do in many vertebrates. The most well-studied of these regions in decapods occurs within a soma cluster, known as cluster 10, located in the deutocerebrum. Cluster 10 in crayfish and lobsters is composed of the somata of two anatomically and functionally distinct classes of projection neurons: olfactory lobe (OL) projection neurons and accessory lobe (AL) projection neurons. While adult-generated cells in cluster 10 survive for at least a year, their final phenotypes remain unknown. To address this question, we combined BrdU labeling of proliferating cells with specific neuronal and glial markers and tracers to examine the differentiation of newborn cells in cluster 10 of the crayfish, Cherax destructor. Our results show that large numbers of adult-generated cells in cluster 10 differentiate into neurons expressing the neuropeptide crustacean-SIFamide. No evidence was obtained suggesting that cells differentiate into glia. The functional phenotypes of newborn neurons in cluster 10 were examined by combining BrdU immunocytochemistry with the application of dextran dyes to different brain neuropils. These studies showed that while the majority of cells born during the early postembryonic development of C. destructor differentiate in AL projection neurons, neurogenesis in adult crayfish is characterized by the addition of both OL and AL projection neurons. In addition to our examination of neurogenesis in the olfactory pathway, we provide the first evidence that adult neurogenesis is also a characteristic feature of the optic neuropils of decapod crustaceans.

Immunolocalization of Na+,K+-ATPase in the branchial cavity during the early development of the crayfish Astacus leptodactylus (Crustacea, Decapoda)

The ontogeny of osmoregulation was examined in the branchial cavity of embryonic and early post-embryonic stages of the crayfish Astacus leptodactylus maintained in freshwater, at the sub-cellular level through the detection of the sodium-potassium adenosine triphosphatase (Na(+),K(+)-ATPase). The embryonic rate of development was calculated according to the eye index (EI) which was 430-450 microm at hatching. The distribution of the enzyme was identified by immunofluorescence microscopy using a monoclonal antibody IgGalpha5 raised against the avian alpha-subunit of the Na(+),K(+)-ATPase. Immunoreactivity staining, indicating the presence of Na(+), K(+)-ATPase appeared in the gills of late embryos (EI>/=400 microm), i.e. a few days before hatching time, and steadily increased throughout the late embryonic and early post-embryonic development. The appearance of the enzyme correlates with the ability to osmoregulate which also occurs late in the embryonic development at EI 410-420 microm and with tissue differentiation within the gill filaments. These observations indicate that the physiological shift from osmoconforming embryos to hyper-regulating late embryos and post-hatching stages in freshwater must originate partly from the differentiation in the gill epithelia of ionocytes which are the site of ion pumping, as suggested by the location of Na(+),K(+)-ATPase. Only the gills were immunostained and a lack of specific staining was noted in the lamina and the branchiostegites. Therefore, osmoregulation through Na(+)active uptake is likely achieved in embryos at the gill level; all the newly formed gills in embryos function in ion regulation; other parts of the branchial chamber such as the branchiostegites and lamina do not appear to be involved in osmoregulation.

Embryonic and early postembryonic development of the burrowing crayfish, Virilastacus araucanius (Faxon, 1914) (Decapoda, Parastacidae) under laboratory conditions

The stages and duration of the embryonic and early postembryonic development of the burrowing crayfish, Virilastacus araucanius are described, in water at temperatures between 10.0 and 21.0?C, with 8.5 to 9.0 mg/1 of dissolved oxygen, pH 6.8 to 8.5, and hardness of 49.8 ppm CaC03. The morphological changes observed on the egg surface allow to distinguish 5 embryonic stages. After hatching, two moults separate three juvenile stages. The first two juvenile stages lack uropods and remain attached to the female. In stage 3, the juvenile is similar to the adult, both in morphology and behaviour, and becomes independent from the mother. Embryonic development lasts 120 days, and the postembryonic stages take another 20 days until the emergence of juvenile stage 3. The development is direct, with incubation of large eggs, rich in yolk, and parental care over juvenile stages 1 and 2.

Insulin and hepatic cholestasis during the early post-embryonic development of gilt-head sea bream, Sparus aurata

This work is aimed at demonstrating the influence of insulin in the triggering of hepatic cholestasis in young gilt-head sea bream larvae reared under experimental conditions. The results are based on an immunological assay of insulin and an ultrastructural study of the yolk syncytial layer and the liver. Compared to fed larvae, fasting gilt-head sea bream larvae displayed a substantial increase in insulin level correlated with dysfunction of the yolk syncytial layer and hepatic histopathology. This correlation was verified in larvae reared in sea water containing insulin. Ultrastructural observations suggested that insulin affects lipoprotein secretion by the yolk syncytial layer. The failure of plasmatic lipoproteins would then cause dysfunction of the biliary lipid secretion mechanisms and, hence, trigger hepatic cholestasis. These results in gilt-head sea bream show for the first time the influence of insulin in the triggering of hepatic cholestasis during the early development of a vertebrate.

Cytological detection of the main phases of lipid metabolism during early post-embryonic development in three teleost species: Dicentrarchus labrax, Sparus aurata and Stizostedion lucioperca

The aim of this report is the synthetic presentation of observations related to ultrastructural aspects of the lipid metabolism during the ontogenesis of trophic mechanisms in three teleost species, the sea bass, Dicentrarchus labrax, the sea bream, Sparus aurata and the pike-perch, Stizostedion lucioperca. The results have shown the respective roles of the vitelline syncytium, the intestine, the liver and the exocrine pancreas during the change from an endogenous lipid source, the yolk vesicle, to an exogenous lipid one, food. They make it possible to stress the close correlation between the development of the biliary function, that of the exocrine function of the pancreas and that of the intestinal absorption of lipids. These activities established during the endotrophic stage are slight at the beginning of trophic life and then increase at the end of the endo-exotrophic stage. Analysis of the results suggests the occurrence of four physiological phases characteristic in early lipid metabolism establishing the main heads in acquisition of the trophic autonomy according to a pattern similar to that of mammals.

Cooperative action of SLR1 and SLR2 is required for lateral root-specific cell elongation in maize.

Lateral roots play an important role in water and nutrient uptake largely by increasing the root surface area. In an effort to characterize lateral root development in maize (Zea mays), we have isolated from Mutator (Mu) transposon stocks and characterized two nonallelic monogenic recessive mutants: slr1 and slr2 (short lateral roots1 and 2), which display short lateral roots as a result of impaired root cell elongation. The defects in both mutants act specifically during early postembryonic root development, affecting only the lateral roots emerging from the embryonic primary and seminal roots but not from the postembryonic nodal roots. These mutations have no major influence on the aboveground performance of the affected plants. The double mutant slr1; slr2 displays a strikingly different phenotype than the single mutants. The defect in slr1; slr2 does not only influence lateral root specific cell elongation, but also leads to disarranged cellular patterns in the primary and seminal roots. However, the phase-specific nature of the single mutants is retained in the double mutant, indicating that the two loci cooperate in the wild type to maintain the lateral root specificity during a short time of early root development.

Early Postembryonic Neural Development in the Zebrafish: A 3-D Reconstruction of Forebrain Proliferation Zones Shows their Relation to Prosomeres

Early Postembryonic Neural Development in the Zebrafish: A 3-D Reconstruction of Forebrain Proliferation Zones Shows their Relation to Prosomeres

Early postembryonic neural development in the zebrafish: a 3-D reconstruction of forebrain proliferation zones shows their relation to prosomeres.

Based on a section-by-section analysis of the morphology (combined silver/Nissl stain) and of the distribution of proliferation zones (immunohistochemical detection of the proliferating cell nuclear antigen) in the zebrafish (Danio rerio) forebrain at 5 days postfertilization, we created a three-dimensional reconstruction of proliferation zones of that developmental stage. The resulting model visualizes the size, number, location and morphology of forebrain proliferation zones. The latter foreshadow closely adult neuroanatomical forebrain entities. Furthermore, the detailed distribution of proliferation zones in the posterior forebrain - but not in the more anterior secondary prosencephalon - supports a segmental prosomeric organization.

Late postembryonic development of the symbiotic light organ of Euprymna scolopes (Cephalopoda: Sepiolidae).

The symbiotic light organ of the sepiolid squid Euprymna scolopes undergoes significant anatomical, morphological, and biochemical changes during development. Previously we described the embryonic organogenesis and early postembryonic development of the light organ. During embryogenesis, tissues are developed that will promote the onset of an association with Vibrio fischeri, the light organ symbiont. Upon inoculation, and in response to the first interactions with the bacterial symbionts, the light organ undergoes a dramatic morphogenesis during the first 4-5 days of postembryonic development. Here we describe the final developmental stage of the light organ system, a period of late postembryonic development in which particular tissues of the light organ mature that eventually mediate the functional symbiosis. The maturation of the light organ occurs within 1 to 2 weeks posthatch and entails two principal processes: (1) changes in the shape of the organ and elaboration of the accessory tissues that modify the bacterially produced light; and (2) branching of the epithelial crypts, where the bacterial symbionts reside, and restriction of epithelial cell proliferation to the deepest branches of the crypts. The gross morphological changes of the organ occur in the absence of V. fischeri, although rudiments of the ciliated field of the hatchling remain in animals not exposed to the microbial symbiont.

NADPH-diaphorase activity in the nervous system of the embryonic and juvenile pond snail, Lymnaea stagnalis.

Nicotinamide-adenine-dinucleotide-phosphate-diaphorase (NADPH-d) histochemistry has been applied in the present study to determine the distribution of putative nitric oxide (nitric oxide synthase)-producing cells during embryonic and early postembryonic development in the pond snail, Lymnaea stagnalis L., with special reference to the nervous system. The first NADPH-d-positive structures appear as early as 18% of development (E18, trochophore stage) and correspond to the pair of protonephridia. These structures later show disintegration, although after metamorphosis (E26=75%) staining of their individually spreading cells can be observed until hatching. Peripheral sensory neurons in the foot, mantle edge and lips, and their afferents projecting to the central nervous system reveal NADPH-d activity in the postmetamorphosis period (E25-E27=E60%-E80%) of embryogenesis. After hatching (P1-P3), a number of stained sensory cells appear in the pharynx and esophagus. Some NADPH-d positive neuronal perikarya occur in the pedal and pleural ganglia, and a few weakly stained cells in the cerebral and buccal ganglia of juvenile snails. At the same time, a continuous bundle of reactive fibers is formed in the neuropil both through and through around the circumesophageal ganglion ring. The localization of NADPH-d activity in the developing nervous system of Lymnaea suggests that nitric oxide participates mainly in sensory processes. However, its role in specific intraganglionic integrative events cannot be excluded following embryonic metamorphosis.

Insulin during the Early Postembryonic Development of the Gilt-Head Sea Bream,Sparus aurata:Ultrastructural, Immunohistochemical, and Biochemical Studies

Insulin was sought during the early postembryonic development of gilt-head sea bream,Sparus aurata,using ultrastructural, immunohistochemical and biochemical techniques. The endocrine pancreas appeared at hatching (Day 0) as a single cluster of morphologically similar cells. Secretory granules formed from Day 1 onwards but the cells could only be identified as insulin-producing B cells at the end of the endotrophic period (Day 3–Day 4). Insulin-immunoreactive cells were detected in the pancreatic primordium from hatching onwards and their number increased after the end of the endo-exotrophic period. Early insulin production was also found using an ELISA method on homogenates of prelarvae and larvae. Insulin levels were fairly high during the endotrophic period, decreased strongly at mouth opening, and then increased at the end of the endo-exocrine period. The origin and role of the large amount of hormone detected during the strictly endotrophic phase of ontogenesis are discussed in light of data on other vertebrates.

Endocrine and neuroendocrine regulations in embryos and larvae of crustaceans

Summary This review deals with the studies which have been conducted for the past 30 years on the endocrine and neuroendocrine regulations in embryos and larvae of crustaceans, mostly in decapods. Y-organs, mandibular organs and the X-organ sinus gland complex of the eyestalks are present in the first post-embryonic instar of most investigated species. Y-organs, the X-organs and the sinus glands have also been located in embryos of a few species. Larval molting appears to be regulated in a way similar to that in adults involving a MIH-ecdysteroid system. Evidence points to a control of metamorphosis through the eyestalks. Experimental evidence points to a neuroendocrine control of changes in pigmentation and of osmoregulation. Progress in the isolation and characterization of the hormones and neurohormones controlling these metabolic changes in adults should help and promote further research on regulation during the embryonic and early postembryonic development.

Biliary lipid secretion during early post-embryonic development in three fishes of aquacultural interest: Sea bass, Dicentrarchus labrax L., sea bream, Sparus aurata L., and pike-perch, Stizostedion lucioperca (L)

The mechanism of biliary lipid secretion, which is poorly documented in high vertebrates and unknown in fish, was studied using cytochemistry and electron microscopy during early post-embryonic development in three teleostean species of aquacultural interest: sea bass, Dicentrarchus labrax L., sea bream, Sparus aurata L., and pike-perch, Stizostedion luciopera (L). Lipids that could be involved in biliary secretion were found in different parts of the hepatic system. VLDL-like particles were observed in the endoplasmic reticulum and in some Golgi vesicles of hepatocytes. In other vesicles of Golgi areas and in pericanalicular vesicles, lipids appear as finely granular and even homogenous materials. These vesicles present acid phosphatase activity. Lipids are also found in the lumen of bile canaliculi, cholangioles, cystic duct, and bile vesicle. These results suggest involvement of the hepatocyte endoplasmic reticulum and Golgi apparatus in the synthesis of biliary lipids that would then be transported by vesicles and secreted in the biliary tract through exocytosis. During ontogenesis, development of the Golgi apparatus in hepatocytes leads to high production of lipid-containing pericanalicular vesicles, at mouth opening. This process decreases in pike-perch and stops in sea bass and sea bream during the following 4 to 5 days. It then resumes and increases in all three species. These results are in agreement with data concerning the development of biliary secretion in mammals. J. Exp. Zool. 277:365–370, 1997. © 1997 Wiley-Liss, Inc.

Abbreviated Larval Development of the Freshwater Prawn, Magrobrachium Iheringi (Ortmann, 1897) (Decapoda, Palaemonidae), Reared in the Laboratory

The present paper describes and illustrates the early post-embryonic development of the freshwater prawn Macrobrachium iheringi (Ortmann, 1897) completely. This species presents an abbreviated larval development of the advanced type, consisting of two zoeal stages before metamorphosing to megalopa. Benthic behaviour is already displayed by the newly hatched zoea. Both zoeae and megalopa are lecithotrophic. Live or inert food particles are captured or collected only after the third moult (juvenile stage) when mouthparts and chelipeds become well developed and fully functional.