Swimbladder gas gland cells cultured on permeable supports regain their characteristic polarity

Comparative transcriptome analysis of the swimbladder reveals expression signatures in response to low oxygen stress in channel catfish, Ictalurus punctatus

Channel catfish is the leading aquaculture species in the US, and one of the reasons for its application in aquaculture is its relatively high tolerance against hypoxia. However, hypoxia can still cause huge economic losses to the catfish industry. Studies on hypoxia tolerance, therefore, are important for aquaculture. Fish swimbladder has been considered as an accessory respiration organ surrounded by a dense capillary countercurrent exchange system. In this regard, we conducted RNA-Seq analysis with swimbladder samples of catfish under hypoxic and normal conditions to determine if swimbladder was responsive to low oxygen treatment and to reveal genes, their expression patterns, and pathways involved in hypoxia responses in catfish. A total of 155 differentially expressed genes (DEGs) were identified from swimbladder of adult catfish, whereas a total of 2,127 DEGs were identified from swimbladder of fingerling catfish under hypoxic condition as compared with untreated controls. Subsequent pathway analysis revealed that many DEGs under hypoxia were involved in HIF signaling pathway ( nos2, eno2, camk2d2, prkcb, cdkn1a, eno1, and tfrc), MAPK signaling pathway (voltage-dependent calcium channel subunit genes), PI3K/Akt/mTOR signaling pathway ( itga6, g6pc, and cdkn1a), Ras signaling pathway ( efna3 and ksr2), and signaling by VEGF ( fn1, wasf3, and hspb1) in catfish swimbladder. This study provided insights into regulation of gene expression and their involved gene pathways in catfish swimbladder in response to low oxygen stresses.

The role of extrinsic and intrinsic factors in the evolution of the control of pulmonary surfactant maturation during development in the amniotes

Pulmonary surfactant is a mixture of lipids and proteins that is secreted by alveolar Type II cells. It reduces alveolar surface tension and hence the work of breathing. Despite the tremendous diversity of lung structures amongst the vertebrates, the composition of surfactant is highly conserved. Conserved elements of the surfactant system amongst distantly related species are likely to be crucial factors for successful lung development. Understanding the mechanisms by which the surfactant system becomes operational in animals with dramatically different birthing strategies and in distantly related species will provide important information about the role of the surfactant system in the commencement of air breathing and the processes regulating surfactant maturation and secretion. In mammals, the embryonic maturation of the surfactant system is controlled by a host of factors, including glucocorticoids, thyroid hormones, and autonomic neurotransmitters. Here we review the mechanisms controlling the maturation of surfactant production, including birthing strategy, phylogeny, lung structure, and posthatching environment. Using four species of egg-laying amniote (chicken, dragon lizard, sea turtle, and crocodile) previously described in detail and the large amount of information available for mammals, we examine the hypothesis that the control of surfactant production is dependent on glucocorticoids (dexamethasone [Dex]), thyroid hormones (T3), and autonomic neurotransmitters (epinephrine and carbachol). We also examine whether the overall intrinsic pattern of the control of surfactant maturation is conserved throughout the vertebrate radiation and then how the environment (extrinsic factors) may account for the observed differences in the patterns of development. We also discuss the utility of a coculture system of embryonic Type II cells and fibroblasts to determine the evolutionary pattern behind the control of surfactant and to demonstrate that the surfactant system matures under multihormonal control. We demonstrate that Dex and T3 are stimulators of surfactant production during embryonic development, but they lose their efficacy closer to hatching or birth. Epinephrine stimulates surfactant secretion beyond 75% of development and also after hatching or birth. Carbachol stimulates surfactant secretion in the bearded dragon and saltwater crocodile but not in the sea turtle, chicken, or mammals. It is likely that the differences in control of surfactant development are likely to be primarily related to metabolic activity and the duration of incubation (i.e., the "speed" of development). Moreover, the hormones examined appear important in promoting development and therefore appear conserved within the amniotes. However, the autonomic neurotransmitters induced different responses in different species. Hence, some factors are crucial for the proper maturation of the surfactant system, whereas others vary throughout evolution without being detrimental to the overall function of the system.