RESUMO
Nuclear and plastid division in the monoplastidic, unicellular eustigmatophyte alga Nannochloropsis oculata (Heterokonta) was investigated by electron microscopy. The outermost of four membranes of the secondary plastid is continuous with the outer nuclear envelope membrane to form a nucleus-plastid continuum (NPC). Such physical continuity between the nucleus and the plastid is maintained throughout the cell cycle. Mitosis takes place in a closed spindle. In prophase, a barrel-shaped nuclear pole body (BR-NPB), emanating microtubules towards the cytoplasm, was detected in the vicinity of the nuclear poles. In metaphase, instead of the BR-NPB, a boomerang-shaped nuclear pole body (BM-NPB) occupied the spindle poles, projecting microtubules towards the opposite pole. The BR- and BM-NPB may function as a microtubule organizing centre (MTOC) but are distinct in morphology from any known MTOCs. During anaphase/telophase, the nucleus undergoes constriction with the microtubules penetrating the nucleus along the pole-to-pole spindle axis. The final stage of the nuclear division takes place in an unusual fashion such that the compartment of the inner nuclear envelope divides in advance of that of the outer nuclear envelope. Such unusual nuclear division is discussed in relevance to transmission of the secondary plastid. The present study provides the first report for nuclear and plastid division in Eustigmatophyceae.
Assuntos
Divisão do Núcleo Celular , Eucariotos/fisiologia , Plastídeos/fisiologia , Eucariotos/citologia , Eucariotos/ultraestrutura , Microscopia Eletrônica , Centro Organizador dos Microtúbulos/fisiologia , Mitose , Fuso Acromático/fisiologiaRESUMO
We have isolated and characterized a ventralized mutant in medaka (the Japanese killifish; Oryzias latipes), which turned out to have a mutation in the chordin gene. The mutant exhibits ventralization of the body axis, malformation of axial bones, over-bifurcation of yolk sac blood vessels, and laterality defects in internal organs. The mutant exhibits variability of phenotypes, depending on the culture temperature, from embryos with a slightly ventralized phenotype to those without any head and trunk structures. Taking advantages of these variable and severe phenotypes, we analyzed the role of Chordin-dependent tissues such as the notochord and Kupffer's vesicle (KV) in the establishment of left-right axis in fish. The results demonstrate that, in the absence of the notochord and KV, the medaka lateral plate mesoderm autonomously and bilaterally expresses spaw gene in a default state.
Assuntos
Padronização Corporal/genética , Glicoproteínas/genética , Peptídeos e Proteínas de Sinalização Intercelular/genética , Mutação , Oryzias/genética , Animais , Células Cultivadas , Embrião não Mamífero , Notocorda , Oryzias/embriologia , Fenótipo , TemperaturaRESUMO
Recent studies have revealed that a cilium-generated liquid flow in the node has a crucial role in the establishment of the left-right (LR) axis in the mouse. In fish, Kupffer's vesicle (KV), a teleost-specific spherical organ attached to the tail region, is known to have an equivalent role to the mouse node during LR axis formation. However, at present, there has been no report of an asymmetric gene expressed in KV under the control of fluid flow. Here we report the earliest asymmetric gene in teleost KV, medaka charon, and its regulation. Charon is a member of the Cerberus/DAN family of proteins, first identified in zebrafish. Although zebrafish charon was reported to be symmetrically expressed in KV, medaka charon displays asymmetric expression with more intense expression on the right side. This asymmetric expression was found to be regulated by KV flow because symmetric and up-regulated charon expression was observed in flow-defective embryos with immotile cilia or disrupted KV. Taken together, medaka charon is a reliable gene marker for LR asymmetry in KV and thus, will be useful for the analysis of the early steps downstream of the fluid flow.
Assuntos
Oryzias/embriologia , Oryzias/genética , Sequência de Aminoácidos , Estruturas Animais/embriologia , Estruturas Animais/fisiologia , Animais , Sequência de Bases , Líquidos Corporais/fisiologia , Padronização Corporal , Clonagem Molecular , DNA Complementar/genética , Proteínas de Peixes/genética , Regulação da Expressão Gênica no Desenvolvimento , Dados de Sequência Molecular , Mutação , Proteína Nodal , Oligodesoxirribonucleotídeos Antissenso/genética , Oryzias/fisiologia , Interferência de RNA , Homologia de Sequência de Aminoácidos , Transdução de Sinais , Fator de Crescimento Transformador beta/genéticaRESUMO
Somitogenesis is a critical step during the formation of metameric structures in vertebrates. Recent studies in mouse, chick, zebrafish and Xenopus have revealed that several factors, such as T-box genes, Notch/Delta, Wnt, retinoic acid and FGF signaling, are involved in the specification of nascent somites. By interacting with these pathways, the Mesp2-like bHLH transcription factors are transiently expressed in the anterior presomitic mesoderm and play a crucial role in somite formation. The regulatory mechanisms of Mesp2 and its related genes during somitogenesis have been studied in mouse and Xenopus. However, the precise mechanism that regulates the transcriptional activity of Mesp2 has yet to be determined. In our current report, we identify the essential enhancer element of medaka mesp-b, an orthologue of mouse Mesp2, using transgenic techniques and embryo manipulation. Our results demonstrate that a region of approximately 2.8 kb, upstream of the mesp-b gene, is responsible for both the initiation and anterior localization of mesp-b transcription within a somite primordium. Furthermore, putative motifs for both T-box transcription factors and Notch/Delta signaling are present in this enhancer region and are essential for activity.
