Polyadenylation of Na(+)-K(+)-ATPase beta 1-subunit during early development of Xenopus laevis

Leucine-rich repeat containing 8A contributes to the expansion of brain ventricles in zebrafish embryos

The sodium osmotic gradient is necessary for the initiation of brain ventricle inflation, but a previous study predicted that organic and inorganic osmolytes play equivalently important roles in osmotic homeostasis in astrocytes. To test whether organic osmoregulation also plays a role in brain ventricle inflation, the core component for volume-regulated anion and organic osmolyte channel, lrrc8a, was investigated in the zebrafish model. RT-PCR and whole-mount in situ hybridization indicated that both genes were ubiquitously expressed through to 12 hpf, and around the ventricular layer of neural tubes and the cardiogenic region at 24 hpf. Knocking down either one lrrc8a paralog with morpholino oligos resulted in abnormalities in circulation at 32 hpf. Morpholino oligos or CRISPR interference against either paralog led to smaller brain ventricles at 24 hpf. Either lrrc8aa or lrrc8ab mRNA rescued the phenotypic penetrance in both lrrc8aa and lrrc8ab morphants. Supplementation of taurine in the E3 medium and overexpression csad mRNA also rescued lrrc8aa and lrrc8ab morphants. Our results indicate that the two zebrafish lrrc8a paralogs are maternal message genes and are ubiquitously expressed in early embryos. The two genes play redundant roles in the expansion of brain ventricles and the circulatory system and taurine contributes to brain ventricle expansion via the volume-regulated anion and organic osmolyte channels.

Epithelial sodium transport and its control by aldosterone: the story of our internal environment revisited

Transcription and translation require a high concentration of potassium across the entire tree of life. The conservation of a high intracellular potassium was an absolute requirement for the evolution of life on Earth. This was achieved by the interplay of P- and V-ATPases that can set up electrochemical gradients across the cell membrane, an energetically costly process requiring the synthesis of ATP by F-ATPases. In animals, the control of an extracellular compartment was achieved by the emergence of multicellular organisms able to produce tight epithelial barriers creating a stable extracellular milieu. Finally, the adaptation to a terrestrian environment was achieved by the evolution of distinct regulatory pathways allowing salt and water conservation. In this review we emphasize the critical and dual role of Na(+)-K(+)-ATPase in the control of the ionic composition of the extracellular fluid and the renin-angiotensin-aldosterone system (RAAS) in salt and water conservation in vertebrates. The action of aldosterone on transepithelial sodium transport by activation of the epithelial sodium channel (ENaC) at the apical membrane and that of Na(+)-K(+)-ATPase at the basolateral membrane may have evolved in lungfish before the emergence of tetrapods. Finally, we discuss the implication of RAAS in the origin of the present pandemia of hypertension and its associated cardiovascular diseases.

Bioelectromagnetics in morphogenesis

Understanding the factors that allow biological systems to reliably self-assemble consistent, highly complex, four dimensional patterns on many scales is crucial for the biomedicine of cancer, regeneration, and birth defects. The role of chemical signaling factors in controlling embryonic morphogenesis has been a central focus in modern developmental biology. While the role of tensile forces is also beginning to be appreciated, another major aspect of physics remains largely neglected by molecular embryology: electromagnetic fields and radiations. The continued progress of molecular approaches to understanding biological form and function in the post genome era now requires the merging of genetics with functional understanding of biophysics and physiology in vivo. The literature contains much data hinting at an important role for bioelectromagnetic phenomena as a mediator of morphogenetic information in many contexts relevant to embryonic development. This review attempts to highlight briefly some of the most promising (and often underappreciated) findings that are of high relevance for understanding the biophysical factors mediating morphogenetic signals in biological systems. These data originate from contexts including embryonic development, neoplasm, and regeneration.

Early embryonic expression of ion channels and pumps in chick and Xenopus development

An extensive body of literature implicates endogenous ion currents and standing voltage potential differences in the control of events during embryonic morphogenesis. Although the expression of ion channel and pump genes, which are responsible for ion flux, has been investigated in detail in nervous tissues, little data are available on the distribution and function of specific channels and pumps in early embryogenesis. To provide a necessary basis for the molecular understanding of the role of ion flux in development, we surveyed the expression of ion channel and pump mRNAs, as well as other genes that help to regulate membrane potential. Analysis in two species, chick and Xenopus, shows that several ion channel and pump mRNAs are present in specific and dynamic expression patterns in early embryos, well before the appearance of neurons. Examination of the distribution of maternal mRNAs reveals complex spatiotemporal subcellular localization patterns of transcripts in early blastomeres in Xenopus. Taken together, these data are consistent with an important role for ion flux in early embryonic morphogenesis; this survey characterizes candidate genes and provides information on likely embryonic contexts for their function, setting the stage for functional studies of the morphogenetic roles of ion transport.

Xenopus Na,K-ATPase: primary sequence of the beta2 subunit and in situ localization of alpha1, beta1, and gamma expression during pronephric kidney development

The osmoregulatory function of the pronephric kidney, the first excretory organ of the vertebrate embryo, is essential for embryonic survival. The transport systems engaged in pronephric osmotic regulation are however poorly understood. The Na,K-ATPase is the key component in renal solute transport and water homeostasis. In the present study, we characterized the alpha, beta, and gamma subunits of the Na,K-ATPase of the developing Xenopus embryo. In addition to the known alpha1, beta1, beta3 and gamma subunits, we report here the identification of a novel cDNA encoding the Xenopus beta2 subunit. We demonstrate by in situ hybridization that each Xenopus Na,K-ATPase subunit exhibits a distinct tissue-specific and developmentally regulated expression pattern. We found that the developing pronephric kidney expresses alpha1, beta1, and gamma subunits uniformly along the entire length of the nephron. Onset of pronephric Na,K-ATPase subunit expression occurred in a coordinated fashion indicating that a common regulatory mechanism may initiate pronephric transcription of these genes. The ability to engage in active Na+ reabsorption appears to be established early in pronephric development, since Na,K-ATPase expression was detected well before the completion of pronephric organogenesis. Furthermore, Na,K-ATPase expression defines at the molecular level the onset of maturation phase during pronephric kidney organogenesis. Taken together, our studies reveal a striking conservation of Na,K-ATPase subunit expression between pronephric and metanephric kidneys. The pronephric kidney may therefore represent a simplified model to dissect the regulatory mechanisms underlying renal Na,K-ATPase subunit expression.

Primary neuronal differentiation in Xenopus embryos is linked to the beta(3) subunit of the sodium pump

In amphibian embryos, activation of additional sodium pumps in neural plate cell membranes ensures that neural plate-derived neurons differentiate subsequently in the neural tube. When the sodium pump is inhibited during the mid-neural fold stages, neuronal differentiation fails. The effect is irreversible. We find that these events operate through the Na pump beta(3) subunit. When neural plate-specific Na pumps are activated, transcripts for beta(3) decline precipitately during the mid-neural fold stages, first in the neural plate and then in the dorsal mesoderm. As the neural tube closes, beta(3) returns, specifically in motor neurons and interneurons. Inhibition of the Na pump with the cardiac glycoside strophanthidin prevents the normal fall in beta(3) during neurulation: beta(3) is maintained in the neural plate until the neural tube closes, but lost from the dorsal mesoderm. Complete elimination of beta(3) transcripts from dorsal structures then occurs. Inhibiting the Na pump does not induce cell death (assessed by TUNEL staining) in the nervous system. Transcripts for X-Delta, NeuroD, and GSK3beta are not affected by inhibition of the Na pump. Xotch and N-tubulin transcripts fall to very low levels and Xotch disappears permanently from the nervous system. When beta(3) transcript expression is maintained throughout neurulation, by over expression of injected mRNAs, Xotch is eliminated from the neural tube and somites and switches to the ectoderm.

Expression of the beta2-subunit and apical localization of Na+-K+-ATPase in metanephric kidney

During kidney organogenesis, the Na+-K+-ATPase pump is not restricted to the basolateral plasma membrane of the renal epithelial cell but is instead either localized to the apical and lateral membrane sites of the early nephron or expressed in a nonpolarized distribution in the newly formed collecting ducts. The importance of Na+-K+-ATPase beta-subunit expression in the translocation of the Na+-K+-ATPase to the plasma membrane raises the question as to which beta-subunit isoform is expressed during kidney organogenesis. Immunocytochemical, Western analysis and RNase protection studies showed that both beta2-subunit protein and beta2 mRNA are expressed in the early gestation to midgestation human metanephric kidney. In contrast, although beta1 mRNA abundance is equivalent to that of the beta2-subunit in the metanephric kidney, the beta1-subunit protein was not detected in early to midgestation metanephric kidney samples. Immunocytochemical analysis revealed that both alpha1- and beta2-subunits were present in the apical epithelial plasma membranes of distal nephron segments of early stage nephrons, maturing loops of Henle, and collecting ducts during kidney development. We also detected a significant increase in alpha1 and beta1 mRNA after birth with a marked reduction in beta2 mRNA abundance associated with an increase in alpha1- and beta1-subunit proteins and loss of beta2 protein expression. These studies support the conclusion that the expression of the beta2-subunit in the fetal kidney may be an important mechanism controlling polarization of the Na+-K+-ATPase pump in the epithelia of the developing nephron during kidney organogenesis.