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The blastula Chordin- and Noggin-expressing (BCNE) center comprises animal-dorsal and marginal-dorsal cells of the amphibian blastula and contains the precursors of the brain and the gastrula organizer. Previous findings suggested that the BCNE behaves as a homogeneous cell population that only depends on nuclear ß-catenin activity but does not require Nodal and later segregates into its descendants during gastrulation. In contrast to previous findings, in this work, we show that the BCNE does not behave as a homogeneous cell population in response to Nodal antagonists. In fact, we found that chordin.1 expression in a marginal subpopulation of notochordal precursors indeed requires Nodal input. We also establish that an animal BCNE subpopulation of cells that express both, chordin.1 and sox2 (a marker of pluripotent neuroectodermal cells), and gives rise to most of the brain, persisted at blastula stage after blocking Nodal. Therefore, Nodal signaling is required to define a population of chordin.1+ cells and to restrict the recruitment of brain precursors within the BCNE as early as at blastula stage. We discuss our findings in Xenopus in comparison to other vertebrate models, uncovering similitudes in early brain induction and delimitation through Nodal signaling.

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Marine angelfish (family: Pomacanthidae) are among the most sought-after fish species in the saltwater aquarium trade. However, there is a lack of information in the literature on their early ontogeny. The objective of this study was to describe the embryonic and early larval development of two dwarf angelfish, the bicolour angelfish, Centropyge bicolor and the coral beauty angelfish, Centropyge bispinosa. The eggs of these two species were obtained from spontaneous spawning of the broodstock fish in captivity and incubated at 26.0 ± 0.2°C throughout the study. Fertilized eggs (n = 15) of both species are transparent, pelagic and spherical; the mean diameters of the eggs were measured at 703.6 ± 7.8 µm for C. bicolor and 627.6 ± 7.8 µm for C. bispinosa. The eggs of both species possessed a narrow perivitelline space, smooth and thin chorion, a homogenous and non-segmented yolk as well as a single oil globule. Overall, the observed embryonic development pattern of C. bicolor and C. bispinosa was very similar, and the main difference was the embryonic pigmentation pattern, which only became evident close to hatching. Larvae of both species started hatching at 13 h 30 min after fertilization, and the larval characteristics of both species also showed high levels of similarities. However, the mouth opening time for C. bicolor was 72 h after hatching (AH) and 96 AH for C. bispinosa. In general, the observed early ontogeny of C. bicolor and C. bispinosa also resembled that of other Centropyge species documented in the literature.

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The developmental adaptations of the marsupial frogs Gastrotheca riobambae and Flectonotus pygmaeus (Hemiphractidae) are described and compared with frogs belonging to seven additional families. Incubation of embryos by the mother in marsupial frogs is associated with changes in the anatomy and physiology of the female, modifications of oogenesis, and extraordinary changes in embryonic development. The comparison of early development reveals that gene expression is highly conserved. However, the timing of gene expression varies between frog species. There are two modes of gastrulation according to the onset of convergent extension. In gastrulation mode 1, convergent extension is an intrinsic mechanism of gastrulation. This gastrulation mode occurs in frogs with aquatic reproduction, such as Xenopus laevis. In gastrulation mode 2, convergent extension occurs after the completion of gastrulation movements. Gastrulation mode 2 occurs in frogs with terrestrial reproduction, such as the marsupial frog, G. riobambae. The two modes of frog gastrulation resemble the two transitions toward meroblastic cleavage of ray-finned fishes (Actinopterygii). The comparison indicates that a major event in the evolution of frog terrestrial development is the separation of convergent extension from gastrulation.

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The vestigial gene (vg) was first characterized in Drosophila and several homologues were identified in vertebrates and called vestigial like 1-4 (vgll1-4). Vgll proteins interact with the transcription factors TEF-1 and MEF-2 through a conserved region called TONDU (TDU). Vgll4s are characterized by two tandem TDU domains which differentiate them from other members of the vestigial family. In Xenopus two genes were identified as vgll4. Our bioinformatic analysis demonstrated that these two genes are paralogues and must be named differently. We designated them as vgll4 and vgll4l. In situ hybridization analysis revealed that the expression of these two genes is rather different. At gastrula stage, both were expressed in the animal pole. However, at neurula stage, vgll4 was mainly expressed in the neural plate and neural folds, while vgll4l prevailed in the neural folds and epidermis. From the advanced neurula stage onward, expression of both genes was strongly enhanced in neural tissues, anterior neural plate, migrating neural crest, optic and otic vesicles. Nevertheless, there were some differences: vgll4 presented somite expression and vgll4l was localized at the skin and notochord. Our results demonstrate that Xenopus has two orthologues of the vgll4 gene, vgll4 and vgll4l with differential expression in Xenopus embryos and they may well have different roles during development.

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El pargo colorado (Lutjanus colorado) es una especie con un alto valor comercial en el mercado mexicano, con potencial para su cultivo. Hasta la fecha no existen estudios sobre su reproducción, cultivo larvario y engorda en cautiverio. El presente trabajo es el primer reporte sobre la descripción a detalle del desarrollo embrionario de la especie bajo condiciones de cultivo. Los huevos fertilizados viables del pargo colorado son pelágicos, esféricos, transparentes y con una sola gota de aceite. Midieron 0,77±0,09 mm de diámetro y la gota de aceite 0,14±0,01 mm. La primera división ocurrió a las 0,05 horas post fertilización (HPF). La eclosión se llevó a cabo a las 17,22 HPF bajo las condiciones del presente estudio. Las larvas recién eclosionadas midieron 1,8±0,1 mm de longitud total (LT). El desarrollo embrionario de esta especie fue similar a la descrita para especies de la misma familia. Los resultados del presente estudio aportan información básica para iniciar el desarrollo de la biotecnología para la producción de semilla de esta especie a escala comercial.

The Colorado snapper (Lutjanus colorado) is one of the most commercially important fish species in México and it is considered a suitable candidate for culture. Until now, no research has been carried out on its reproduction, larviculture and fattening in captivity. This study is the first description of embryonic development of this species under controlled conditions. Fertilized eggs of Colorado snapper are pelagic, spherical and transparent and contain one drop of oil. Eggs measured 0.77±0.09 mm and the drop of oil 0.14±0.01 mm. First cell division occurred at 0.05 h post-fertilization (HPF), hatching at 17.22 HPF under the above described conditions. Larvae total length (LT) was 1.8±0.1 mm. Embryonic development of this species was similar to other lutjanidae species. These results provide basic information for developing the necessary biotechnology for commercial seed production of the Colorado snapper.

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The morphology of the gastrocoel roof plate and the presence of cilia in this structure were examined in embryos of four species of frogs. Embryos of Ceratophrys stolzmanni (Ceratophryidae) and Engystomops randi (Leiuperidae) develop rapidly, provide comparison for the analysis of gastrocoel roof plate development in the slow-developing embryos of Epipedobates machalilla (Dendrobatidae) and Gastrotheca riobambae (Hemiphractidae). Embryos of the analyzed frogs develop from eggs of different sizes, and display different reproductive and developmental strategies. In particular, dorsal convergence and extension and archenteron elongation begin during gastrulation in embryos of rapidly developing frogs, as in Xenopus laevis. In contrast, cells that involute during gastrulation are stored in the large circumblastoporal collar that develops around the closed blastopore in embryos of slow-developing frogs. Dorsal convergence and extension only start after blastopore closure in slow-developing frog embryos. However, in the neurulae, a gastrocoel roof plate develops, despite the accumulation of superficial mesodermal cells in the circumblastoporal collar. Embryos of all four species develop a ciliated gastrocoel roof plate at the beginning of neurulation. Accordingly, fluid-flow across the gastrocoel roof plate is likely the mechanism of left-right asymmetry patterning in these frogs, as in X. laevis and other vertebrates. A ciliated gastrocoel roof plate, with a likely origin as superficial mesoderm, is conserved in frogs belonging to four different families and with different modes of gastrulation.

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Development of Pomacea canaliculata from the gastrula stage until the first day after hatching is described. Trochophore embryos are developed after gastrulation, showing the prototroch as a crown of ciliated orange-brownish cells. However, no true veliger embryos are formed, since the prototroch does not fully develop into a velum. Afterward, the connection between the fore- and midgut is permeated and the midgut becomes full of the pink-reddish albumen, which is stored into a central archenteron's lake, from where it is accumulated into the large cells forming the midgut wall ("giant cells"). Electron microscopy of giant cells in late embryos showed that albumen is engulfed by large endocytic vesicles formed between the irregular microvilli at the top of these cells. By the end of intracapsular development, giant cells become gradually replaced by two new epithelial cell types which are similar to those found in the adult midgut gland: the pre-columnar and the pre-pyramidal cells. Pre-columnar cells have inconspicuous basal nuclei and are crowned by stereocilia, between which small endocytic vesicles are formed. Pre-pyramidal cells have large nuclei with 2-3 nucleoli and show a striking development of the rough endoplasmic reticulum. The genesis of the three cell lineages (giant, pre-columnar and pre-pyramidal cells) is hypothetically attributed to epithelial streaks that occur at both sides of the midgut since early stages of development.

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BACKGROUND: Recent evidence from global studies of gene expression indicates that transcriptomes are more complex than expected. Xenopus has been typically used as a model organism to study early embryonic development, particularly dorso-ventral patterning. In order to identify novel transcripts involved in dorso-ventral patterning, we compared dorsal and ventral transcriptomes of Xenopus tropicalis at the gastrula stage using serial analysis of gene expression (SAGE). RESULTS: Of the experimental tags, 54.5% were confidently mapped to transcripts and 125 showed a significant difference in their frequency of occurrence between dorsal and ventral libraries. We selected 20 differentially expressed tags and assigned them to specific transcripts using bioinformatics and reverse SAGE. Five mapped to transcripts with known dorso-ventral expression and the frequency of appearance for these tags in each library is in agreement with the expression described by other methods. The other 15 tags mapped to transcripts with no previously described asymmetric expression along the dorso-ventral axis. The differential expression of ten of these novel transcripts was validated by in situ hybridization and/or RT-PCR. We can estimate that this SAGE experiment provides a list of at least 86 novel transcripts with differential expression along the dorso-ventral axis. Interestingly, the expression of some novel transcripts was independent of beta-catenin. CONCLUSIONS: Our SAGE analysis provides a list of novel transcripts with differential expression in the dorso-ventral axis and a large number of orphan tags that can be used to identify novel transcripts and to improve the current annotation of the X. tropicalis genome.

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