Xepac protein and IP3/Ca2+ pathway implication during Xenopus laevis vitellogenesis

Are Cell Junctions Implicated in the Regulation of Vitellogenin Uptake? Insights from an RNAseq-Based Study in Eel, Anguilla australis

At the onset of puberty, ovarian follicles become competent to incorporate large amounts of vitellogenin (Vtg). Using an RNAseq-based approach, transcriptomes from pre-vitellogenic (PV) and early vitellogenic (EV) ovaries from wild-caught eel, Anguilla australis, were compared to investigate the expression of specific genes encoding cell junction proteins that could be involved in regulating Vtg uptake. Partial support was found for the mechanical barrier hypothesis proposing that the access of Vtg to the oolemma is restricted by a tight junction (TJ) network within the granulosa cell layer, which changes between the PV and EV stage. Among 25 genes encoding TJ-constituting proteins, five were down-regulated and two were up-regulated. A chemical barrier hypothesis stating that gap junctions (GJs) are involved in modulating Vtg uptake was not supported, as only five GJs were found to be expressed in the ovary with no significant changes in expression between stages. Furthermore, the endocytic pathway was found to be up-regulated during the PV-EV transition. Finally, the study showed that gene expression patterns may help identify suitable candidates involved in the regulation of Vtg uptake, and provided novel sequence data for A. australis, including putative Vtg receptors corresponding to Lr8 and Lrp13 members of the low-density lipoprotein receptor family.

Dynamic changes in mitochondrial DNA, morphology, and fission during oogenesis of a seasonal-breeding teleost, Pampus argenteus

Mitochondria play crucial roles during oocyte development. In this study, we have investigated mitochondrial morphology, mtDNA, Ca²⁺-ATP enzyme activity, and mitochondrial fission factor (mff) expression levels during oogenesis of the silver pomfret Pampus argenteus. The mtDNA increased with oocyte development, and mitochondrial morphology and distribution were stage-specific. In the perinucleolar oocytes, oval mitochondria were dispersed in the cytoplasm. In previtellogenic oocytes, mitochondria massively increased and aggregated, forming mitochondrial clouds. At the same time, two morphologically different types of mitochondria had been distinguished, one of which was elongated with well-developed cristae, and the other was round with distorted and fused cristae. During vitellogenesis, the increases in mitochondria with well-developed cristae and in Ca²⁺-ATPase enzymatic activity were accompanied by an accumulation of yolk substance, suggesting the possible participation of mitochondria in the formation of vitellogenesis. Furthermore, we examined the cDNA of mff its transcript levels in relation to oocyte development. The transcript levels of mff were high in the perinucleolar stage, increasing to the highest level at the previtellogenic stage. Immunocytochemistry showed that MFF was detected in the cytoplasm of previtellogenic and midvitellogenic oocytes. We speculated that the mff-mediated mitochondrial fission may play a crucial role in oocyte development, especially in vitellogenesis.

Hydrogen Peroxide Signaling in Plant Development and Abiotic Responses: Crosstalk with Nitric Oxide and Calcium

Hydrogen peroxide (H2O2), as a reactive oxygen species, is widely generated in many biological systems. It has been considered as an important signaling molecule that mediates various physiological and biochemical processes in plants. Normal metabolism in plant cells results in H2O2 generation, from a variety of sources. Also, it is now clear that nitric oxide (NO) and calcium (Ca(2+)) function as signaling molecules in plants. Both H2O2 and NO are involved in plant development and abiotic responses. A wide range of evidences suggest that NO could be generated under similar stress conditions and with similar kinetics as H2O2. The interplay between H2O2 and NO has important functional implications to modulate transduction processes in plants. Moreover, close interaction also exists between H2O2 and Ca(2+) in response to development and abiotic stresses in plants. Cellular responses to H2O2 and Ca(2+) signaling systems are complex. There is quite a bit of interaction between H2O2 and Ca(2+) signaling in responses to several stimuli. This review aims to introduce these evidences in our understanding of the crosstalk among H2O2, NO, and Ca(2+) signaling which regulates plant growth and development, and other cellular and physiological responses to abiotic stresses.