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Animal Pole (animal + pole)
Selected AbstractsOoplasmic segregation in the zebrafish zygote and early embryo: Pattern of ooplasmic movements and transport pathwaysDEVELOPMENTAL DYNAMICS, Issue 8 2010Ricardo Fuentes Abstract Patterns of cytoplasmic movements and organization of transport pathways were examined in live or fixed zygotes and early zebrafish embryos using a variety of techniques. The zygote blastodisc grows by accumulation of ooplasm, transported to the animal pole from distinct sectors of ecto- and endoplasm at different speeds and developmental periods, using specific pathways or streamers. Slow transport (5 ,m/min) occurs during the first interphase along short streamers, whereas fast transport (9.6,40 ,m/min) takes place during the first cleavage division along axial and meridional streamers. Interconnections between streamers allow cargoes to change their speed and final destination. A similar sequence of events occurs during the following divisions. A complex network of microtubules and actin filaments in the endo- and ectoplasm appears to be involved in the transport of inclusions and mRNAs. Actin-dependent intermittent pulsations provoked high-speed back-and-forth movements of cytoplasm that may contribute to redistribution of organelles and maternal determinants. Developmental Dynamics 239:2172,2189, 2010. © 2010 Wiley-Liss, Inc. [source] Developmental analysis of activin-like kinase receptor-4 (ALK4) expression in Xenopus laevisDEVELOPMENTAL DYNAMICS, Issue 2 2005Yumei Chen Abstract The type I transforming growth factor-beta (TGF,) receptor, activin-like kinase-4 (ALK4), is an important regulator of vertebrate development, with roles in mesoderm induction, primitive streak formation, gastrulation, dorsoanterior patterning, and left,right axis determination. To complement previous ALK4 functional studies, we have analyzed ALK4 expression in embryos of the frog, Xenopus laevis. Results obtained with reverse transcriptase-polymerase chain reaction indicate that ALK4 is present in both the animal and vegetal poles of blastula stage embryos and that expression levels are relatively constant amongst embryos examined at blastula, gastrula, neurula, and early tail bud stages. However, the tissue distribution of ALK4 mRNA, as assessed by whole-mount in situ hybridization, was found to change over this range of developmental stages. In the blastula stage embryo, ALK4 is detected in cells of the animal pole and the marginal zone. During gastrulation, ALK4 is detected in the outer ectoderm, involuting mesoderm, blastocoele roof, dorsal lip, and to a lesser extent, in the endoderm. At the onset of neurulation, ALK4 expression is prominent in the dorsoanterior region of the developing head, the paraxial mesoderm, and midline structures, including the prechordal plate and neural folds. Expression in older neurula stage embryos resolves to the developing brain, somites, notochord, and neural crest; thereafter, additional sites of ALK4 expression in tail bud stage embryos include the spinal cord, otic placode, developing eye, lateral plate mesoderm, branchial arches, and the bilateral heart fields. Together, these results not only reflect the multiple developmental roles that have been proposed for this TGF, receptor but also define spatiotemporal windows in which ALK4 may function to modulate fundamental embryological events. Developmental Dynamics 232:393,398, 2005. © 2004 Wiley-Liss, Inc. [source] Comparative folliculogenesis and spermatogenesis of four teleost fish from a Reservoir in south-eastern BrazilACTA ZOOLOGICA, Issue 4 2010Yuri Simões Martins Abstract Martins, Y.S., Moura, D.F., Santos, G.B., Rizzo, E. and Bazzoli, N. 2009. Comparative folliculogenesis and spermatogenesis of four teleost fish from a Reservoir in south-eastern Brazil. ,Acta Zoologica (Stockholm). 91: 466,473. This study provides a comparative analysis of gametogenesis of neotropical teleosts Metynnis maculatus, Megalancistrus parananus, Cichla kelberi and Satanoperca pappaterra, through histological, histochemical and histometric techniques. In the ooplasm of C. kelberi and S. pappaterra conspicuous lipid vesicles were observed, which are characteristic of pelagic eggs produced by marine fishes. Perinucleolar oocytes were identified in the testis of S. pappaterra suggesting that this species is protogynous without functional hermaphroditism, an unusual pattern for neotropical fresh-water fishes. The spermatozoa of the studied species have rounded heads, a characteristic of fish that externally fertilise their eggs. The follicular (granulosa) cells of the vitellogenic oocytes from the studied species were cuboidal or columnar, however, in C. kelberi there were columnar follicular cells at the vegetal pole and cuboidal cells at the animal pole. Variations of the histochemical content were detected in the cortical alveoli and follicular cells of vitellogenic oocytes showing differences in the mechanisms to block polyspermy and egg adhesiveness. Larger oocytes were recorded in species which demonstrated parental care behaviour and smaller oocytes were noted in those species with fractioned spawning. [source] Localization of RNAs in oocytes of Eleutherodactylus coqui, a direct developing frog, differs from Xenopus laevisEVOLUTION AND DEVELOPMENT, Issue 6 2003Yvonne M. Beckham SummaryEleutherodactylus coqui develops directly on land to a frog. The large 3.5-mm oocyte of E. coqui has enough yolk to allow development without a feeding tadpole. In the smaller Xenopus laevis oocyte, 1.3 mm in diameter, mRNAs involved in germ layer formation, such as VegT and Vg1, are localized to the vegetal cortex of the oocyte. We hypothesized that an animal shift has occurred in the localization of the E. coqui Orthologs of VegT and Vg1 due to the large egg size. Through a combination of degenerate reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE), we cloned 1634 bp of EcVegT and 1377 bp of EcVg1. Northern blot analysis shows that the lengths of these transcripts are 2.5 kb and 1.3 kb, respectively. This result suggests that we have obtained the complete Vg1 transcript, although this transcript has an extremely short 3, untranslated region compared with X. laevis, 256 bp and 1268 bp, respectively. Zygotic expression of EcVegT closely resembles that of VegT, supporting their orthology. Radioactive RT-PCR and in situ hybridization demonstrated the presence of EcVegT and EcVg1 predominantly near the animal pole of the oocyte. RT-PCR showed that the animal blastomeres, formed from the first horizontal cleavage, inherit half of the EcVegT and EcVg1 transcripts, although they contain only about 1% of the embryo volume. Our results indicate major differences between the molecular organization of the eggs of X. laevis and E. coqui. [source] Reproductive biology of female big-bellied seahorsesJOURNAL OF FISH BIOLOGY, Issue 3 2004C. W. Poortenaar In this study, ovarian morphology, reproductive condition and sex steroid levels were investigated in the big-bellied seahorse Hippocampus abdominalis, collected by snorkel and SCUBA diving in Wellington Harbour, New Zealand. Within the ovary, oocytes were contained between an outer muscular wall and an inner layer of luminal epithelium. Two germinal ridges ran along the entire length of the ovary. In cross-section, oocytes were arranged in sequential order of development beginning at the germinal ridges and ending at the mature edge. Ovarian lamellae were absent. Vitellogenic and advanced cortical alveoli oocytes were elongated in shape, whereas maturing oocytes were distinctively pear-shaped. Mature oocytes were large (2·6 , 4·4 mm in length) and aligned with the animal pole towards the muscular wall. Reproductively mature females were found throughout the year indicating a protracted reproductive season. The gonado-somatic index was significantly different between all ovarian stages, but the hepato-somatic index was not. Females with previtellogenic ovaries had significantly higher plasma concentrations of testosterone than females with vitellogenic or maturing ovaries. There was no significant difference in plasma concentrations of testosterone between females with vitellogenic or maturing ovaries, or in plasma concentrations of 17,-oestradiol between females in all ovarian stages. This study contributes to the knowledge on the reproductive biology of female syngnathids. [source] Early development of the silver catfish Rhamdia quelen (Quoy & Gaimard, 1824) (Pisces:Heptapteridae) from the São Francisco River Basin, BrazilAQUACULTURE RESEARCH, Issue 2 2009Marcelo Pimenta De Amorim Abstract The silver catfish, Rhamdia quelen, is endemic to North, Central and South America with high aquaculture potential and wide acceptance in the market. Breeder fish were subjected to induced reproduction through hypophysation using a crude common carp pituitary extract. Egg characteristics, oocyte surface ultrastructure and histology of larval ontogenesis until whole yolk resorption were described for the first time for this species. Oocytes and semen were obtained by manual extrusion, and fertilization was conducted using the dry method. After fertilization, eggs were kept in incubators at 24 °C. The embryonic development was monitored using a stereomicroscope every 10 min until hatching. To analyse the larval development, larvae samples were collected from incubators daily until the fifth day, fixed in Bouin's fluid and subjected to routine histological techniques. The oocyte extrusion occurred 8 h after the second hormone dose at 26 °C. The oocytes were spherical, non-adhesive and yellow, with a diameter of 1471.75±47.63 ,m. Scanning electron microscopy revealed a thin jelly coat covering the zona radiata in the animal pole around the micropyle. The blastopore closure occurred within 8 h after fertilization, and the fertilization rate was 79.9±5.2% at 24 °C. Embryonic development was completed within 25 h 30 min after fertilization. The complete resorption of the yolk and the formation of the digestive system organs and the mouth opening occurred on the fifth day, indicating a need for exogenous feeding. The results of this study provide information important for improvement in R. quelen culture and management. [source] | |||||||||||||