The Origin and Evolution of the Surfactant System in Fish: Insights into the Evolution of Lungs and Swim Bladders

Origin and stepwise evolution of vertebrate lungs

Lungs are essential respiratory organs in terrestrial vertebrates, present in most bony fishes but absent in cartilaginous fishes, making them an ideal model for studying organ evolution. Here we analysed single-cell RNA sequencing data from adult and developing lungs across vertebrate species, revealing significant similarities in cell composition, developmental trajectories and gene expression patterns. Surprisingly, a large proportion of lung-related genes, coexpression patterns and many lung enhancers are present in cartilaginous fishes despite their lack of lungs, suggesting that a substantial genetic foundation for lung development existed in the last common ancestor of jawed vertebrates. In addition, the 1,040 enhancers that emerged since the last common ancestor of bony fishes probably contain lung-specific elements that led to the development of lungs. We further identified alveolar type 1 cells as a mammal-specific alveolar cell type, along with several mammal-specific genes, including ager and sfta2, that are highly expressed in lungs. Functional validation showed that deletion of sfta2 in mice leads to severe respiratory defects, highlighting its critical role in mammalian lung features. Our study provides comprehensive insights into the evolution of vertebrate lungs, demonstrating how both regulatory network modifications and the emergence of new genes have shaped lung development and specialization across species.

Symbiogenesis redicts the monism of the cosmos

Symbiogenesis has been systematically exploited to understand consciousness as the aggregate of our physiology. The Symbiogenic mechanism for assimilation of factors in the environment formulates the continuum from inside the cell to the Cosmos, both consciousness and cosmology complying with the Laws of Nature. Since Symbiogenesis is 'constructive', whereas eliminating what threatens us is 'destructive', why do we largely practice Symbiogenesis? Hypothetically, Symbiogenesis recursively simulates the monism of our origin, recognizing 'something bigger than ourselves'. That perspective explains many heretofore unexplained aspects of consciousness, such as mind, epigenetic inheritance, physiology, behaviors, social systems, mathematics, the Arts, from an a priori perspective. Moreover, there is an energetic continuum from Newtonian to Quantum Mechanics, opening up to a novel way of understanding the 'true nature of our being', not as 'materialism', but instead being the serial homeostatic control of energy. The latter is consistent with the spirit of Claude Bernard and Walter B. Cannon's perspectives on physiology. Such a paradigm shift is overdue, given that materialism is causing the destruction of the Earth and ourselves.

Pulmonary arteries in coelacanths shed light on the vasculature evolution of air-breathing organs in vertebrates

To date, the presence of pulmonary organs in the fossil record is extremely rare. Among extant vertebrates, lungs are described in actinopterygian polypterids and in all sarcopterygians, including coelacanths and lungfish. However, vasculature of pulmonary arteries has never been accurately identified neither in fossil nor extant coelacanths due to the paucity of fossil preservation of pulmonary organs and limitations of invasive studies in extant specimens. Here we present the first description of the pulmonary vasculature in both fossil and extant actinistian, a non-tetrapod sarcopterygian clade, contributing to a more in-depth discussion on the morphology of these structures and on the possible homology between vertebrate air-filled organs (lungs of sarcopterygians, lungs of actinopterygians, and gas bladders of actinopterygians).

Toxicogenomics of Five Cytostatics in Fathead Minnow (Pimephales promelas) Larvae

In this study, the toxicogenomic effects of five cytostatics (tamoxifen, methotrexate, capecitabine, cyclophosphamide, and ifosfamide) on fathead minnow (Pimephales promelas) larvae were evaluated. Post-fertilization eggs were exposed to increasing concentrations of the drugs for six days. The expression levels of two genetic biomarkers for toxicity and four thyroid hormone-related gene pathways were measured. Interestingly, the results showed that all concentrations of the five cytostatics affect the transcription levels of both toxicity biomarker genes. Additionally, the thyroid hormone-related genes had different expression levels than the control, with the most significant changes observed in those larvae exposed to cyclophosphamide and ifosfamide. While a previous study found no effects on fish morphology, this study suggests that the five cytostatics modify subtle molecular responses of P. promelas, highlighting the importance of assessing multibiological level endpoints throughout the lifecycle of animals to understand the full portrait of potential effects of cytostatics and other contaminants.

Ecotoxicity of commonly used oilfield-based emulsifiers on Guinean Tilapia (Tilapia guineensis) using histopathology and behavioral alterations as protocol

This study examined the histological aberrations in the gill and liver tissues and behavioural changes of Tilapia guineensis fingerlings exposed to lethal concentrations of used Oilfield-based emulsifiers for 96 h. Various concentrations of the surfactants were tested, ranging from 0.0 to 15.0 ml/L. The behaviour of the fish was observed throughout the experiment, and the results showed that increasing concentrations of the surfactants led to progressively abnormal behaviour, including hyperventilation and altered opercular beat frequency. These behavioural changes indicated respiratory distress and neurotoxic effects. Histological analysis revealed structural aberrations in the gill and liver tissues, with higher concentrations causing more severe damage, such as lesions, necrosis, inflammation, and cellular degeneration. This implies that surfactants released even at low concentrations are capable of inducing changes in the tissues of aquatic organisms. These findings highlight the toxic effects of the surfactants on fish health and provide biomarkers of toxicity. Future research should focus on understanding the specific mechanisms and long-term consequences of surfactant toxicity on fish genetic composition, populations, and ecosystems to implement effective conservation measures.

Surface tension in biological systems - a common problem with a variety of solutions

Water is of fundamental importance to living organisms, not only as a universal solvent to maintain metabolic activity but also due to the effects the physical properties of water have on different organismal structures. In this review, we explore some examples of how living organisms deal with surfaces covered with or in contact with water. While we do not intend to describe all possible forms of interactions in every minute detail, we would like to draw attention to this intriguing interdisciplinary subject and discuss the positive and negative effects of the interaction forces between water molecules and organisms. Topics explored include locomotion on water, wettability of surfaces, benefits of retaining a film of air while submerged (Salvinia effect), surface tension of water inhibiting air-breathing, accumulation of water in small tubes, surface tension in non-mammalian and mammalian respiratory systems. In each topic, we address the importance of interactions with water and the adaptations seen in an organism to solve the surface-related challenges, trying to explore the different selective pressures acting onto different organisms allowing exploring or compensating these surface-related interactions.

The evolution of the various structures required for hearing in Latimeria and tetrapods

Sarcopterygians evolved around 415 Ma and have developed a unique set of features, including the basilar papilla and the cochlear aqueduct of the inner ear. We provide an overview that shows the morphological integration of the various parts needed for hearing, e.g., basilar papilla, tectorial membrane, cochlear aqueduct, lungs, and tympanic membranes. The lagena of the inner ear evolved from a common macula of the saccule several times. It is near this lagena where the basilar papilla forms in Latimeria and tetrapods. The basilar papilla is lost in lungfish, certain caecilians and salamanders, but is transformed into the cochlea of mammals. Hearing in bony fish and tetrapods involves particle motion to improve sound pressure reception within the ear but also works without air. Lungs evolved after the chondrichthyans diverged and are present in sarcopterygians and actinopterygians. Lungs open to the outside in tetraposomorph sarcopterygians but are transformed from a lung into a swim bladder in ray-finned fishes. Elasmobranchs, polypterids, and many fossil fishes have open spiracles. In Latimeria, most frogs, and all amniotes, a tympanic membrane covering the spiracle evolved independently. The tympanic membrane is displaced by pressure changes and enabled tetrapods to perceive airborne sound pressure waves. The hyomandibular bone is associated with the spiracle/tympanic membrane in actinopterygians and piscine sarcopterygians. In tetrapods, it transforms into the stapes that connects the oval window of the inner ear with the tympanic membrane and allows hearing at higher frequencies by providing an impedance matching and amplification mechanism. The three characters-basilar papilla, cochlear aqueduct, and tympanic membrane-are fluid related elements in sarcopterygians, which interact with a set of unique features in Latimeria. Finally, we explore the possible interaction between the unique intracranial joint, basicranial muscle, and an enlarged notochord that allows fluid flow to the foramen magnum and the cochlear aqueduct which houses a comparatively small brain.

Ontogeny, phylogeny and cellular energy flows for evolution

The case has previously been made for the 'Singularity of Nature" based on homologies between the inorganic and the organic. But a causal explanation for those homologies was not provided. The following is a hypothetical way to understand how and why physiology emerged from physics, providing a predictive model for cell-molecular evolution.

Avian surfactant protein (SP)-A2 first arose in an early tetrapod before the divergence of amphibians and gradually lost the collagen domain

The air-liquid interface of the mammalian lung is lined with pulmonary surfactants, a mixture of specific proteins and lipids that serve a dual purpose-enabling air-breathing and protection against pathogens. In mammals, surfactant proteins A (SP-A) and D (SP -D) are involved in innate defence of the lung. Birds seem to lack the SP-D gene, but possess SP-A2, an additional SP-A-like gene. Here we investigated the evolution of the SP-A and SP-D genes using computational gene prediction, homology, simulation modelling and phylogeny with published avian and other vertebrate genomes. PCR was used to confirm the identity and expression of SP-A analogues in various tissue homogenates of zebra finch and turkey. In silico analysis confirmed the absence of SP-D-like genes in all 47 published avian genomes. Zebra finch and turkey SP-A1 and SP-A2 sequences, confirmed by PCR of lung homogenates, were compared with sequenced and in silico predicted vertebrate homologs to construct a phylogenetic tree. The collagen domain of avian SP-A1, especially that of zebra finch, was dramatically shorter than that of mammalian SP-A. Amphibian and reptilian genomes also contain avian-like SP-A2 protein sequences with a collagen domain. NCBI Gnomon-predicted avian and alligator SP-A2 proteins all lacked the collagen domain completely. Both avian SP-A1 and SP-A2 sequences form separate clades, which are most closely related to their closest relatives, the alligators. The C-terminal carbohydrate recognition domain (CRD) of zebra finch SP-A1 was structurally almost identical to that of rat SP-A. In fact, the CRD of SP-A is highly conserved among all the vertebrates. Birds retained a truncated version of mammalian type SP-A1 as well as a non-collagenous C-type lectin, designated SP-A2, while losing the large collagenous SP-D lectin, reflecting their evolutionary trajectory towards a unidirectional respiratory system. In the context of zoonotic infections, how these evolutionary changes affect avian pulmonary surface protection is not clear.

Using the swimbladder as a respiratory organ and/or a buoyancy structure-Benefits and consequences

A swimbladder is a special organ present in several orders of Actinopterygians. As a gas-filled cavity it contributes to a reduction in overall density, but on descend from the water surface its contribution as a buoyancy device is very limited because the swimbladder is compressed by increasing hydrostatic pressure. It serves, however, as a very efficient organ for aerial gas exchange. To avoid the loss of oxygen to hypoxic water at the gills many air-breathing fish show a reduced gill surface area. This, in turn, also reduces surface area available for other functions, so that breathing air is connected to a number of physiological adjustments with respect to ion homeostasis, acid-base regulation and nitrogen excretion. Using the swimbladder as a buoyancy structure resulted in the loss of its function as an air-breathing organ and required the development of a gas secreting mechanism. This was achieved via the Root effect and a countercurrent arrangement of the blood supply to the swimbladder. In addition, a detachable air space with separated blood supply was necessary to allow the resorption of gas from the swimbladder. Gas secretion as well as gas resorption are slow phenomena, so that rapid changes in depth cannot instantaneously be compensated by appropriate volume changes. As gas-filled cavities the respiratory swimbladder and the buoyancy device require surfactant. Due to high oxygen partial pressures inside the bladder air-exposed tissues need an effective reactive oxygen species defense system, which is particularly important for a swimbladder at depth.

Life is a mobius strip

If you cut a mobius strip in half, the edges form a Trefoil Knot, which can be untied to form a circle, proving it's a true mathematical knot. The cell is a homologue of the mathematical knot since it, too, must be able to unknot itself to form the egg and sperm meiotically in order to reproduce. The homology between a knot and a cell is thought-provoking biologically because the Trefoil Knot is a metaphor for the endoderm, ectoderm and mesoderm, the three germ layers of the gastrula that ultimately produce the embryo, beginning with the zygote. Upon further consideration, the cell membrane is like a mobius strip, forming one continuous surface between the inner environment of the cell and the outer environment. However, it is not formed by taking a circular surface, cutting it, twisting it and attaching the two ends as you would conventionally to form a mobius strip. Conversely, David Bohm's Explicate Order forms a boundary with the Implicate Order. That lipid boundary is the prima facie mobius strip that divides the infinite surface of the Implicate Order into inside and outside by 'recalling' its pre-adapted state as lipid molecules before there was an inside or outside.

Changes in Nkx2.1, Sox2, Bmp4, and Bmp16 expression underlying the lung-to-gas bladder evolutionary transition in ray-finned fishes

The key to understanding the evolutionary origin and modification of phenotypic traits is revealing the responsible underlying developmental genetic mechanisms. An important organismal trait of ray-finned fishes is the gas bladder, an air-filled organ that, in most fishes, functions for buoyancy control, and is homologous to the lungs of lobe-finned fishes. The critical morphological difference between lungs and gas bladders, which otherwise share many characteristics, is the general direction of budding during development. Lungs bud ventrally and the gas bladder buds dorsally from the anterior foregut. We investigated the genetic underpinnings of this ventral-to-dorsal shift in budding direction by studying the expression patterns of known lung genes (Nkx2.1, Sox2, and Bmp4) during the development of lungs or gas bladder in three fishes: bichir, bowfin, and zebrafish. Nkx2.1 and Sox2 show reciprocal dorsoventral expression patterns during tetrapod lung development and are important regulators of lung budding; their expression during bichir lung development is conserved. Surprisingly, we find during gas bladder development, Nkx2.1 and Sox2 expression are inconsistent with the hypothesis that they regulate the direction of gas bladder budding. Bmp4 is expressed ventrally during lung development in bichir, akin to the pattern during mouse lung development. During gas bladder development, Bmp4 is not expressed. However, Bmp16, a paralogue of Bmp4, is expressed dorsally in the developing gas bladder of bowfin. Bmp16 is present in the known genomes of Actinopteri (ray-finned fishes excluding bichir) but absent from mammalian genomes. We hypothesize that Bmp16 was recruited to regulate gas bladder development in the Actinopteri in place of Bmp4.

Histological Study of Suprabranchial Chamber Membranes in Anabantoidei and Clariidae Fishes

Simple Summary

Air-breathing fish constitute a broad evolutionary group of fish, which are generally characterized by distinctive phenotypical plasticity. These fishes usually inhabit waters where oxygen deficiency occurs periodically, which is why they have developed a variety of accessory respiratory organs (AROs) that may be used in an obligatory or a facultative manner. Knowledge of the structure of these organs is important for both the breeding and the conservation of these fish species. The aim of this study was to conduct a comparative histological analysis of two types of AROs found in the Anabantoidei suborder and the Clariidae family, both of which are freshwater fish taxa of high ecological and commercial importance.

Abstract

Accessory respiratory organs (AROs) are a group of anatomical structures found in fish, which support the gills and skin in the process of oxygen uptake. AROs are found in many fish taxa and differ significantly, but in the suborder Anabantoidei, which has a labyrinth organ (LO), and the family Clariidae, which has a dendritic organ (DO), these structures are found in the suprabranchial cavity (SBC). In this study, the SBC walls, AROs, and gills were studied in anabantoid (Betta splendens, Ctenopoma acutirostre, Helostoma temminckii) and clariid (Clarias angolensis, Clarias batrachus) fishes. The histological structure of the investigated organs was partially similar, especially in relation to their connective tissue core; however, there were noticeable differences in the epithelial layer. There were no significant species-specific differences in the structure of the AROs within the two taxa, but the SBC walls had diversified structures, depending on the observed location. The observed differences between species suggest that the remarkable physiological and morphological plasticity of the five investigated species can be associated with structural variety within their AROs. Furthermore, based on the observed histology of the SBC walls, it is reasonable to conclude that this structure participates in the process of gas exchange, not only in clariid fish but also in anabantoids.

Autophagy Is Required for Maturation of Surfactant-Containing Lamellar Bodies in the Lung and Swim Bladder

Autophagy is an intracellular degradation system, but its physiological functions in vertebrates are not yet fully understood. Here, we show that autophagy is required for inflation of air-filled organs: zebrafish swim bladder and mouse lung. In wild-type zebrafish swim bladder and mouse lung type II pulmonary epithelial cells, autophagosomes are formed and frequently fuse with lamellar bodies. The lamellar body is a lysosome-related organelle that stores a phospholipid-containing surfactant complex that lines the air-liquid interface and reduces surface tension. We find that autophagy is critical for maturation of the lamellar body. Accordingly, atg-deficient zebrafish fail to maintain their position in the water, and type-II-pneumocyte-specific Fip200-deficient mice show neonatal lethality with respiratory failure. Autophagy suppression does not affect synthesis of the surfactant phospholipid, suggesting that autophagy supplies lipids and membranes to lamellar bodies. These results demonstrate an evolutionarily conserved role of autophagy in lamellar body maturation.

A comparative perspective on lung and gill regeneration

The ability to continuously grow and regenerate the gills throughout life is a remarkable property of fish and amphibians. Considering that gill regeneration was first described over one century ago, it is surprising that the underlying mechanisms of cell and tissue replacement in the gills remain poorly understood. By contrast, the mammalian lung is a largely quiescent organ in adults but is capable of facultative regeneration following injury. In the course of the past decade, it has been recognized that lungs contain a population of stem or progenitor cells with an extensive ability to restore tissue; however, despite recent advances in regenerative biology of the lung, the signaling pathways that underlie regeneration are poorly understood. In this Review, we discuss the common evolutionary and embryological origins shared by gills and mammalian lungs. These are evident in homologies in tissue structure, cell populations, cellular function and genetic pathways. An integration of the literature on gill and lung regeneration in vertebrates is presented using a comparative approach in order to outline the challenges that remain in these areas, and to highlight the importance of using aquatic vertebrates as model organisms. The study of gill regeneration in fish and amphibians, which have a high regenerative potential and for which genetic tools are widely available, represents a unique opportunity to uncover common signaling mechanisms that may be important for regeneration of respiratory organs in all vertebrates. This may lead to new advances in tissue repair following lung disease.

Dorsoventral inversion of the air-filled organ (lungs, gas bladder) in vertebrates: RNAsequencing of laser capture microdissected embryonic tissue

How modification of gene expression generates novel traits is key to understanding the evolutionary process. We investigated the genetic basis for the origin of the piscine gas bladder from lungs of ancestral bony vertebrates. Distinguishing these homologous organs is the direction of budding from the foregut during development; lungs bud ventrally and the gas bladder buds dorsally.

Expression of three P4-phospholipid flippases-atp11a, atp11b, and atp11c in zebrafish (Danio rerio)

Cellular membrane asymmetry is a hallmark characteristic of all eukaryotic cells. The balance of phospholipid composition within the cytoplasmic inner leaflet and the extracellular outer leaflet of the plasma membrane (PM) maintains cellular function and vitality. The proper exposure of particular phospholipids is necessary to maintain cellular signalling, controlled apoptosis, and vesicle transportation among other roles. Phospholipid asymmetry is coordinated by P4-type phospholipid transferases (flippases or ATPases). ATP11A, ATP11B, and ATP11C belong to class VI of the P4-flippase family (vertebrates) and are responsible for the movement of phosphatidylserine (PS) from the outer leaflet to the inner leaflet of the PM. To date, there is a lack of knowledge of the tissue specific expression of these three flippases on a whole-organism level in a vertebrate system. Here we have determined the spatial-temporal expression profiles of each gene in a zebrafish model using in situ hybridization and performed comparative phylogenetic analyses with other vertebrates. Our data reveals sequence similarity between vertebrate flippases and specific synteny of zebrafish and human chromosomes. Both atp11b and atp11c are maternally expressed in zebrafish, while zygotic expression analysis demonstrates tissue and temporal specificity for all three genes. atp11a is expressed in the neural crest cells as well as in the developing eye and ear, while atp11b is expressed early in the ventricular epithelial lining and later in the ear. atp11c is expressed in the anterior most rhombomeres of the hindbrain, pharyngeal arches, and liver. Our expression data suggests that each of the three flippases are integral for the development of specific tissues, and aberrant function of either could lead to visual, hearing, neural, or liver dysfunction.

Leger J. Morphology of the Amazonian Teleost Genus Arapaima Using Advanced 3D Imaging

The arapaima is the largest of the extant air-breathing freshwater fishes. Their respiratory gas bladder is arguably the most striking of all the adaptations to living in the hypoxic waters of the Amazon basin, in which dissolved oxygen can reach 0 ppm (0 mg/l) at night. As obligatory air-breathers, arapaima have undergone extensive anatomical and physiological adaptations in almost every organ system. These changes were evaluated using magnetic resonance and computed tomography imaging, gross necropsy, and histology to create a comprehensive morphological assessment of this unique fish. Segmentation of advanced imaging data allowed for creation of anatomically accurate and quantitative 3D models of organs and their spatial relationships. The deflated gas bladder [1.96% body volume (BV)] runs the length of the coelomic cavity, and encompasses the kidneys (0.35% BV). It is compartmentalized by a highly vascularized webbing comprising of ediculae and inter-edicular septa lined with epithelium acting as a gas exchange surface analogous to a lung. Gills have reduced surface area, with severe blunting and broadening of the lamellae. The kidneys are not divided into separate regions, and have hematopoietic and excretory tissue interspersed throughout. The heart (0.21% BV) is encased in a thick layer of lipid rich tissue. Arapaima have an unusually large telencephalon (28.3% brain volume) for teleosts. The characteristics that allow arapaima to perfectly exploit their native environment also make them easy targets for overfishing. In addition, their habitat is at high risk from climate change and anthropogenic activities which are likely to result is fewer specimens living in the wild, or achieving their growth potential of up to 4.5 m in length.

Expression of Acetylcholine- and G protein coupled Muscarinic receptor in the Neuroepithelial cells (NECs) of the obligated air-breathing fish, Arapaima gigas (Arapaimatidae: Teleostei)

The air-breathing specialization has evolved idependently in vertebrates, as many different organs can perfom gas exchange. The largest obligate air-breathing fish from South America Arapaima gigas breathe air using its gas bladder, and its dependence on air breathing increases during its growth. During its development, gill morphology shows a dramatic change, remodeling with a gradual reduction of gill lamellae during the transition from water breathing to air breathing . It has been suggested that in this species the gills remain the main site of O₂ and CO₂ sensing. Consistent with this, we demonstrate for the first time the occurrence of the neuroepithelial cells (NECs) in the glottis, and in the gill filament epithelia and their distal halves. These cells contain a broader spectrum of neurotransmitters (5-HT, acetylcholine, nNOS), G-protein subunits and the muscarininic receptors that are coupled to G proteins (G-protein coupled receptors). We report also for the first time the presence of G alpha proteins coupled with muscarinic receptors on the NECs, that are thought as receptors that initiate the cardiorespiratory reflexes in aquatic vertebrates. Based on the specific orientation in the epithelia and their closest vicinity to efferent vasculatures, the gill and glottal NECs of A. gigas could be regarded as potential O₂ and CO₂ sensing receptors. However, future studies are needed to ascertain the neurophysiological characterization of these cells.

The Lung and Esophagus: Developmental and Regenerative Overlap

Lung and esophageal development and organogenesis involve a complex interplay of signaling pathways and transcriptional factors. Once the lung and esophagus do separate, their epithelial proliferation and differentiation programs share certain common properties that may fuel adaptive responses to injury and subsequent regeneration. Lung and esophageal tissue organogenesis and regeneration provide perspectives on squamous cell cancers and adenocarcinomas in each tissue.

Unitary Physiology

The common relationships among a great variety of biological phenomena seem enigmatic when considered solely at the level of the phenotype. The deep connections in physiology, for example, between the effects of maternal food restriction in utero and the subsequent incidence of metabolic syndrome in offspring, the effects of microgravity on cell polarity and reproduction in yeast, stress effects on jellyfish, and their endless longevity, or the relationship between nutrient abundance and the colonial form in slime molds, are not apparent by phenotypic observation. Yet all of these phenomena are ultimately determined by the Target of Rapamycin (TOR) gene and its associated signaling complexes. In the same manner, the unfolding of evolutionary physiology can be explained by a comparable application of the common principle of cell-cell signaling extending across complex developmental and phylogenetic traits. It is asserted that a critical set of physiologic and phenotypic adaptations emanated from a few crucial, ancestral receptor gene duplications that enabled the successful terrestrial transition of vertebrates from water to land. In combination, mTor and its cognate receptors and a few crucial genetic duplications provide a mechanistic common denominator across a diverse spectrum of biological responses. The proper understanding of their purpose yields a unified concept of physiology and its evolutionary development. © 2018 American Physiological Society. Compr Physiol 8:761-771, 2018.

Thyroid disrupting effects of halogenated and next generation chemicals on the swim bladder development of zebrafish

Endocrine disrupting chemicals (EDCs) can alter thyroid function and adversely affect growth and development. Halogenated compounds, such as perfluorinated chemicals commonly used in food packaging, and brominated flame retardants used in a broad range of products from clothing to electronics, can act as thyroid disruptors. Due to the adverse effects of these compounds, there is a need for the development of safer next generation chemicals. The objective of this study was to test the thyroid disruption potential of old use and next generation halogenated chemicals. Zebrafish embryos were exposed to three old use compounds, perfluorooctanoic acid (PFOA), tetrabromobisphenol A (TBBPA) and tris (1,3-dichloro-2-propyl) phosphate (TDCPP) and two next generation chemicals, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxdie (DOPO) and perfluorobutyric acid (PFBA). Sub-chronic (0-6days post fertilization (dpf)) and chronic (0-28dpf) exposures were conducted at 1% of the concentration known to kill 50% (LC₅₀) of the population. Changes in the surface area of the swim bladder as well as in expression levels of genes involved in the thyroid control of swim bladder inflation were measured. At 6dpf, zebrafish exposed to all halogenated chemicals, both old use and next generation, had smaller posterior swim bladder and increased expression in the gene encoding thyroid peroxidase, tpo and the genes encoding two swim bladder surfactant proteins, sp-a and sp-c. These results mirrored the effects of thyroid hormone-exposed positive controls. Fish exposed to a TPO inhibitor (methimazole, MMI) had a decrease in tpo expression levels at 28dpf. Effects on the anterior swim bladder at 28dpf, after exposure to MMI as well as both old and new halogenated chemicals, were the same, i.e., absence of SB in ∼50% of fish, which were also of smaller body size. Overall, our results suggest thyroid disruption by the halogenated compounds tested via the swim bladder surfactant system. However, with the exception of TBBPA and TDCPP, the concentrations tested (∼5-137ppm) are not likely to be found in the environment.

Evolution of Shh endoderm enhancers during morphological transition from ventral lungs to dorsal gas bladder

Shh signalling plays a crucial role for endoderm development. A Shh endoderm enhancer, MACS1, is well conserved across terrestrial animals with lungs. Here, we first show that eliminating mouse MACS1 causes severe defects in laryngeal development, indicating that MACS1-directed Shh signalling is indispensable for respiratory organogenesis. Extensive phylogenetic analyses revealed that MACS1 emerged prior to the divergence of cartilaginous and bony fishes, and even euteleost fishes have a MACS1 orthologue. Meanwhile, ray-finned fishes evolved a novel conserved non-coding sequence in the neighbouring region. Transgenic assays showed that MACS1 drives reporter expression ventrally in laryngeal epithelium. This activity has been lost in the euteleost lineage, and instead, the conserved non-coding sequence of euteleosts acquired an enhancer activity to elicit dorsal epithelial expression in the posterior pharynx and oesophagus. These results implicate that evolution of these two enhancers is relevant to the morphological transition from ventral lungs to dorsal gas bladder.

Endoderm enhancer MACS1 of Sonic Hedgehog is conserved in animals with lungs. Here, the authors show that mouse without MACS1 has defective laryngeal development, and use phylogenetic analyses to show association of evolutionary lung-gas bladder transition with change of the enhancer.

Critical appraisal of some factors pertinent to the functional designs of the gas exchangers

Respiration acquires O₂ from the external fluid milieu and eliminates CO₂ back into the same. Gas exchangers evolved under certain immutable physicochemical laws upon which their elemental functional design is hardwired. Adaptive changes have occurred within the constraints set by such laws to satisfy metabolic needs for O₂, environmental conditions, respiratory medium utilized, lifestyle pursued and phylogenetic level of development: correlation between structure and function exists. After the inaugural simple cell membrane, as body size and structural complexity increased, respiratory organs formed by evagination or invagination: the gills developed by the former process and the lungs by the latter. Conservation of water on land was the main driver for invagination of the lungs. In gills, respiratory surface area increases by stratified arrangement of the structural components while in lungs it occurs by internal subdivision. The minuscule terminal respiratory units of lungs are stabilized by surfactant. In gas exchangers, respiratory fluid media are transported by convection over long distances, a process that requires energy. However, movement of respiratory gases across tissue barriers occurs by simple passive diffusion. Short distances and large surface areas are needed for diffusion to occur efficiently. Certain properties, e.g., diffusion of gases through the tissue barrier, stabilization of the respiratory units by surfactant and a thin tripartite tissue barrier, have been conserved during the evolution of the gas exchangers. In biology, such rare features are called Bauplans, blueprints or frozen cores. That several of them (Bauplans) exist in gas exchangers almost certainly indicates the importance of respiration to life.

Phenotype as Agent for Epigenetic Inheritance

The conventional understanding of phenotype is as a derivative of descent with modification through Darwinian random mutation and natural selection. Recent research has revealed Lamarckian inheritance as a major transgenerational mechanism for environmental action on genomes whose extent is determined, in significant part, by germ line cells during meiosis and subsequent stages of embryological development. In consequence, the role of phenotype can productively be reconsidered. The possibility that phenotype is directed towards the effective acquisition of epigenetic marks in consistent reciprocation with the environment during the life cycle of an organism is explored. It is proposed that phenotype is an active agent in niche construction for the active acquisition of epigenetic marks as a dominant evolutionary mechanism rather than a consequence of Darwinian selection towards reproductive success. The reproductive phase of the life cycle can then be appraised as a robust framework in which epigenetic inheritance is entrained to affect growth and development in continued reciprocal responsiveness to environmental stresses. Furthermore, as first principles of physiology determine the limits of epigenetic inheritance, a coherent justification can thereby be provided for the obligate return of all multicellular eukaryotes to the unicellular state.

The Unicellular State as a Point Source in a Quantum Biological System

A point source is the central and most important point or place for any group of cohering phenomena. Evolutionary development presumes that biological processes are sequentially linked, but neither directed from, nor centralized within, any specific biologic structure or stage. However, such an epigenomic entity exists and its transforming effects can be understood through the obligatory recapitulation of all eukaryotic lifeforms through a zygotic unicellular phase. This requisite biological conjunction can now be properly assessed as the focal point of reconciliation between biology and quantum phenomena, illustrated by deconvoluting complex physiologic traits back to their unicellular origins.

Life Is Simple-Biologic Complexity Is an Epiphenomenon

Life originated from unicellular organisms by circumventing the Second Law of Thermodynamics using the First Principles of Physiology, namely negentropy, chemiosmosis and homeostatic regulation of calcium and lipids. It is hypothesized that multicellular organisms are merely contrivances or tools, used by unicellular organisms as agents for the acquisition of epigenetic inheritance. The First Principles of Physiology, which initially evolved in unicellular organisms are the exapted constraints that maintain, sustain and perpetuate that process. To ensure fidelity to this mechanism, we must return to the first principles of the unicellular state as the determinants of the primary level of selection pressure during the life cycle. The power of this approach is reflected by examples of its predictive value. This perspective on life is a "game changer", mechanistically rendering transparent many dogmas, teleologies and tautologies that constrain the current descriptive view of Biology.

Improved ROS defense in the swimbladder of a facultative air-breathing erythrinid fish, jeju, compared to a non-air-breathing close relative, traira

The jeju Hoplerythrinus unitaeniatus and the traira Hoplias malabaricus are two closely related erythrinid fish, both possessing a two-chambered physostomous swimbladder. In the jeju the anterior section of the posterior bladder is highly vascularized and the swimbladder is used for aerial respiration; the traira, in turn, is a water-breather that uses the swimbladder as a buoyancy organ and not for aerial oxygen uptake. Observation of the breathing behavior under different levels of water oxygenation revealed that the traira started aquatic surface respiration only under severe hypoxic conditions and did not breathe air. In the jeju air-breathing behavior was observed under normoxic conditions, and the frequency of air-breathing was significantly increased under hypoxic conditions. Unexpectedly, even under hyperoxic conditions (30 mg O₂ L⁻¹) the jeju continued to take air breaths, and compared with normoxic conditions the frequency was not reduced. Because the frequently air-exposed swimbladder tissue faces higher oxygen partial pressures than normally experienced by other fish tissues, it was hypothesized that in the facultative air-breathing jeju, swimbladder tissue would have a higher antioxidative capacity than the swimbladder tissue of the water breathing traira. Measurement of total glutathione (GSSG/GSH) concentration in anterior and posterior swimbladder tissue revealed a higher concentration of this antioxidant in swimbladder tissue as compared to muscle tissue in the jeju. Furthermore, the GSSG/GSH concentration in jeju tissues was significantly higher than in traira tissues. Similarly, activities of enzymes involved in the breakdown of reactive oxygen species were significantly higher in the jeju swimbladder as compared to the traira swimbladder. The results show that the jeju, using the swimbladder as an additional breathing organ, has an enhanced antioxidative capacity in the swimbladder as compared to the traira, using the swimbladder only as a buoyancy organ.

Heterochrony as Diachronically Modified Cell-Cell Interactions

Heterochrony is an enabling concept in evolution theory that metaphorically captures the mechanism of biologic change due to mechanisms of growth and development. The spatio-temporal patterns of morphogenesis are determined by cell-to-cell signaling mediated by specific soluble growth factors and their cognate receptors on nearby cells of different germline origins. Subsequently, down-stream production of second messengers generates patterns of form and function. Environmental upheavals such as Romer’s hypothesized drying up of bodies of water globally caused the vertebrate water-land transition. That transition caused physiologic stress, modifying cell-cell signaling to generate terrestrial adaptations of the skeleton, lung, skin, kidney and brain. These tissue-specific remodeling events occurred as a result of the duplication of the Parathyroid Hormone-related Protein Receptor (PTHrPR) gene, expressed in mesodermal fibroblasts in close proximity to ubiquitously expressed endodermal PTHrP, amplifying this signaling pathway. Examples of how and why PTHrPR amplification affected the ontogeny, phylogeny, physiology and pathophysiology of the lung are used to substantiate and further our understanding through insights to the heterochronic mechanisms of evolution, such as the fish swim bladder evolving into the vertebrate lung, interrelated by such functional homologies as surfactant and mechanotransduction. Instead of the conventional description of this phenomenon, lung evolution can now be understood as adaptive changes in the cellular-molecular signaling mechanisms underlying its ontogeny and phylogeny.

What We Talk About When We Talk About Evolution

Currently, the biologic sciences are a Tower of Babel, having become so highly specialized that one discipline cannot effectively communicate with another. A mechanism for evolution that integrates development and physiologic homeostasis phylogenetically has been identified—cell-cell interactions. By reducing this process to ligand-receptor interactions and their intermediate down-stream signaling partners, it is possible, for example, to envision the functional homologies between such seemingly disparate structures and functions as the lung alveolus and kidney glomerulus, the skin and brain, or the skin and lung. For example, by showing the continuum of the lung phenotype for gas exchange at the cell-molecular level, being selected for increased surface area by augmenting lung surfactant production and function in lowering surface tension, we have determined an unprecedented structural-functional continuum from proximate to ultimate causation in evolution. It is maintained that tracing the changes in structure and function that have occurred over both the short-term history of the organism (as ontogeny), and the long-term history of the organism (as phylogeny), and how the mechanisms shared in common can account for both biologic stability and novelty, will provide the key to understanding the mechanisms of evolution. We need to better understand evolution from its unicellular origins as the Big Bang of biology.

Evolution, Development, and Function of the Pulmonary Surfactant System in Normal and Perturbed Environments

Surfactant lipids and proteins form a surface active film at the air-liquid interface of internal gas exchange organs, including swim bladders and lungs. The system is uniquely positioned to meet both the physical challenges associated with a dynamically changing internal air-liquid interface, and the environmental challenges associated with the foreign pathogens and particles to which the internal surface is exposed. Lungs range from simple, transparent, bag-like units to complex, multilobed, compartmentalized structures. Despite this anatomical variability, the surfactant system is remarkably conserved. Here, we discuss the evolutionary origin of the surfactant system, which likely predates lungs. We describe the evolution of surfactant structure and function in invertebrates and vertebrates. We focus on changes in lipid and protein composition and surfactant function from its antiadhesive and innate immune to its alveolar stability and structural integrity functions. We discuss the biochemical, hormonal, autonomic, and mechanical factors that regulate normal surfactant secretion in mature animals. We present an analysis of the ontogeny of surfactant development among the vertebrates and the contribution of different regulatory mechanisms that control this development. We also discuss environmental (oxygen), hormonal and biochemical (glucocorticoids and glucose) and pollutant (maternal smoking, alcohol, and common "recreational" drugs) effects that impact surfactant development. On the adult surfactant system, we focus on environmental variables including temperature, pressure, and hypoxia that have shaped its evolution and we discuss the resultant biochemical, biophysical, and cellular adaptations. Finally, we discuss the effect of major modern gaseous and particulate pollutants on the lung and surfactant system.

Lung endoderm morphogenesis: gasping for form and function

The respiratory endoderm develops from a small cluster of cells located on the ventral anterior foregut. This population of progenitors generates the myriad epithelial lineages required for proper lung function in adults through a complex and delicately balanced series of developmental events controlled by many critical signaling and transcription factor pathways. In the past decade, understanding of this process has grown enormously, helped in part by cell lineage fate analysis and deep sequencing of the transcriptomes of various progenitors and differentiated cell types. This review explores how these new techniques, coupled with more traditional approaches, have provided a detailed picture of development of the epithelial lineages in the lung and insight into how aberrant development can lead to lung disease.

Pleiotropy as the Mechanism for Evolving Novelty: Same Signal, Different Result

In contrast to the probabilistic way of thinking about pleiotropy as the random expression of a single gene that generates two or more distinct phenotypic traits, it is actually a deterministic consequence of the evolution of complex physiology from the unicellular state. Pleiotropic novelties emerge through recombinations and permutations of cell-cell signaling exercised during reproduction based on both past and present physical and physiologic conditions, in service to the future needs of the organism for its continued survival. Functional homologies ranging from the lung to the kidney, skin, brain, thyroid and pituitary exemplify the evolutionary mechanistic strategy of pleiotropy. The power of this perspective is exemplified by the resolution of evolutionary gradualism and punctuated equilibrium in much the same way that Niels Bohr resolved the paradoxical duality of light as Complementarity.

Developmental Expression and Hypoxic Induction of Hypoxia Inducible Transcription Factors in the Zebrafish

The hypoxia inducible transcription factor (HIF) has been shown to coordinate the hypoxic response of vertebrates and is expressed in three different isoforms, HIF-1α, HIF-2α and HIF-3α. Knock down of either Hif-1α or Hif-2α in mice results in lethality in embryonic or perinatal stages, suggesting that this transcription factor is not only controlling the hypoxic response, but is also involved in developmental phenomena. In the translucent zebrafish embryo the performance of the cardiovascular system is not essential for early development, therefore this study was designed to analyze the expression of the three Hif-isoforms during zebrafish development and to test the hypoxic inducibility of these transcription factors. To complement the existing zfHif-1α antibody we expressed the whole zfHif-2α protein and used it for immunization and antibody generation. Similarly, fragments of the zfHif-3α protein were used for immunization and generation of a zfHif-3α specific antibody. To demonstrate presence of the Hif-isoforms during development [between 1 day post fertilization (1 dpf) and 9 dpf] affinity-purified antibodies were used. Hif-1α protein was present under normoxic conditions in all developmental stages, but no significant differences between the different developmental stages could be detected. Hif-2α was also present from 1 dpf onwards, but in post hatching stages (between 5 and 9 dpf) the expression level was significantly higher than prior to hatching. Similarly, Hif-3α was expressed from 1 dpf onwards, and the expression level significantly increased until 5 dpf, suggesting that Hif-2α and Hif-3α play a particular role in early development. Hypoxic exposure (oxygen partial pressure = 5 kPa) in turn caused a significant increase in the level of Hif-1α protein even at 1 dpf and in later stages, while neither Hif-2α nor Hif-3α protein level were affected. In these early developmental stages Hif-1α therefore appears to be more important for the coordination of hypoxic responsiveness.

The lineage-specific evolution of aquaporin gene clusters facilitated tetrapod terrestrial adaptation

A major physiological barrier for aquatic organisms adapting to terrestrial life is dessication in the aerial environment. This barrier was nevertheless overcome by the Devonian ancestors of extant Tetrapoda, but the origin of specific molecular mechanisms that solved this water problem remains largely unknown. Here we show that an ancient aquaporin gene cluster evolved specifically in the sarcopterygian lineage, and subsequently diverged into paralogous forms of AQP2, -5, or -6 to mediate water conservation in extant Tetrapoda. To determine the origin of these apomorphic genomic traits, we combined aquaporin sequencing from jawless and jawed vertebrates with broad taxon assembly of >2,000 transcripts amongst 131 deuterostome genomes and developed a model based upon Bayesian inference that traces their convergent roots to stem subfamilies in basal Metazoa and Prokaryota. This approach uncovered an unexpected diversity of aquaporins in every lineage investigated, and revealed that the vertebrate superfamily consists of 17 classes of aquaporins (Aqp0 - Aqp16). The oldest orthologs associated with water conservation in modern Tetrapoda are traced to a cluster of three aqp2-like genes in Actinistia that likely arose >500 Ma through duplication of an aqp0-like gene present in a jawless ancestor. In sea lamprey, we show that aqp0 first arose in a protocluster comprised of a novel aqp14 paralog and a fused aqp01 gene. To corroborate these findings, we conducted phylogenetic analyses of five syntenic nuclear receptor subfamilies, which, together with observations of extensive genome rearrangements, support the coincident loss of ancestral aqp2-like orthologs in Actinopterygii. We thus conclude that the divergence of sarcopterygian-specific aquaporin gene clusters was permissive for the evolution of water conservation mechanisms that facilitated tetrapod terrestrial adaptation.

Rapid diversification of FoxP2 in teleosts through gene duplication in the teleost-specific whole genome duplication event

As one of the most conserved genes in vertebrates, FoxP2 is widely involved in a number of important physiological and developmental processes. We systematically studied the evolutionary history and functional adaptations of FoxP2 in teleosts. The duplicated FoxP2 genes (FoxP2a and FoxP2b), which were identified in teleosts using synteny and paralogon analysis on genome databases of eight organisms, were probably generated in the teleost-specific whole genome duplication event. A credible classification with FoxP2, FoxP2a and FoxP2b in phylogenetic reconstructions confirmed the teleost-specific FoxP2 duplication. The unavailability of FoxP2b in Danio rerio suggests that the gene was deleted through nonfunctionalization of the redundant copy after the Otocephala-Euteleostei split. Heterogeneity in evolutionary rates among clusters consisting of FoxP2 in Sarcopterygii (Cluster 1), FoxP2a in Teleostei (Cluster 2) and FoxP2b in Teleostei (Cluster 3), particularly between Clusters 2 and 3, reveals asymmetric functional divergence after the gene duplication. Hierarchical cluster analyses of hydrophobicity profiles demonstrated significant structural divergence among the three clusters with verification of subsequent stepwise discriminant analysis, in which FoxP2 of Leucoraja erinacea and Lepisosteus oculatus were classified into Cluster 1, whereas FoxP2b of Salmo salar was grouped into Cluster 2 rather than Cluster 3. The simulated thermodynamic stability variations of the forkhead box domain (monomer and homodimer) showed remarkable divergence in FoxP2, FoxP2a and FoxP2b clusters. Relaxed purifying selection and positive Darwinian selection probably were complementary driving forces for the accelerated evolution of FoxP2 in ray-finned fishes, especially for the adaptive evolution of FoxP2a and FoxP2b in teleosts subsequent to the teleost-specific gene duplication.

The transcription factor Atonal homolog 8 regulates Gata4 and Friend of Gata-2 during vertebrate development

GATA and Friend of GATA (FOG) form a transcriptional complex that plays a key role in cardiovascular development in both fish and mammals. In the present study we demonstrate that the basic helix-loop-helix transcription factor Atonal homolog 8 (Atoh8) is required for development of the heart in fish but not in mice. Genetic studies reveal that Atoh8 interacts specifically with Gata4 and Fog1 during development of the heart and swim bladder in the fish. Biochemical studies reveal that ATOH8, GATA4, and FOG2 associate in a single complex in vitro. In contrast to fish, ATOH8-deficient mice exhibit normal cardiac development and loss of ATOH8 does not alter cardiac development in Gata4(+/-) mice. This species difference in the role of ATOH8 is explained in part by LacZ and GFP reporter alleles that reveal restriction of Atoh8 expression to atrial but not ventricular myocardium in the mouse. Our findings identify ATOH8 as a novel regulator of GATA-FOG function that is required for cardiac development in the fish but not the mouse. Whether ATOH8 modulates GATA-FOG function at other sites or in more subtle ways in mammals is not yet known.

A quantum model of exaptation: incorporating potentiality into evolutionary theory

The phenomenon of preadaptation, or exaptation (wherein a trait that originally evolved to solve one problem is co-opted to solve a new problem) presents a formidable challenge to efforts to describe biological phenomena using a classical (Kolmogorovian) mathematical framework. We develop a quantum framework for exaptation with examples from both biological and cultural evolution. The state of a trait is written as a linear superposition of a set of basis states, or possible forms the trait could evolve into, in a complex Hilbert space. These basis states are represented by mutually orthogonal unit vectors, each weighted by an amplitude term. The choice of possible forms (basis states) depends on the adaptive function of interest (e.g., ability to metabolize lactose or thermoregulate), which plays the role of the observable. Observables are represented by self-adjoint operators on the Hilbert space. The possible forms (basis states) corresponding to this adaptive function (observable) are called eigenstates. The framework incorporates key features of exaptation: potentiality, contextuality, nonseparability, and emergence of new features. However, since it requires that one enumerate all possible contexts, its predictive value is limited, consistent with the assertion that there exists no biological equivalent to "laws of motion" by which we can predict the evolution of the biosphere.

Why Do We have to Move Fluid to be Able to Breathe?

The ability to breathe air represents a fundamental step in vertebrate evolution that was accompanied by several anatomical and physiological adaptations. The morphology of the air-blood barrier is highly conserved within air-breathing vertebrates. It is formed by three different plies, which are represented by the alveolar epithelium, the basal lamina, and the endothelial layer. Besides these conserved morphological elements, another common feature of vertebrate lungs is that they contain a certain amount of fluid that covers the alveolar epithelium. The volume and composition of the alveolar fluid is regulated by transepithelial ion transport mechanisms expressed in alveolar epithelial cells. These transport mechanisms have been reviewed extensively. Therefore, the present review focuses on the properties and functional significance of the alveolar fluid. How does the fluid enter the alveoli? What is the fate of the fluid in the alveoli? What is the function of the alveolar fluid in the lungs? The review highlights the importance of the alveolar fluid, its volume and its composition. Maintenance of the fluid volume and composition within certain limits is critical to facilitate gas exchange. We propose that the alveolar fluid is an essential element of the air-blood barrier. Therefore, it is appropriate to refer to this barrier as being formed by four plies, namely (1) the thin fluid layer covering the apical membrane of the epithelial cells, (2) the epithelial cell layer, (3) the basal membrane, and (4) the endothelial cells.

Chronic zebrafish PFOS exposure alters sex ratio and maternal related effects in F1 offspring

Perfluorooctanesulfonic acid (PFOS) is an organic contaminant ubiquitous in the environment, wildlife, and humans. Few studies have assessed its chronic toxicity on aquatic organisms. The present study defined the effects of long-term exposure to PFOS on zebrafish development and reproduction. Specifically, zebrafish at 8 h postfertilization (hpf) were exposed to PFOS at 0, 5, 50, and 250 µg/L for five months. Growth suppression was observed in the 250 µg/L PFOS-treated group. The sex ratio was altered, with a significant female dominance in the high-dose PFOS group. Male gonad development was also impaired in a dose-dependent manner by PFOS exposure. Although female fecundity was not impacted, the F1 embryos derived from high-dose exposed females paired with males without PFOS exposure developed severe deformity at early development stages and resulted in 100% larval mortality at 7 d postfertilization (dpf). Perfluorooctanesulfonic acid quantification in embryos indicated that decreased larval survival in F1 offspring was directly correlated to the PFOS body burden, and larval lethality was attributable to maternal transfer of PFOS to the eggs. Lower-dose parental PFOS exposure did not result in decreased F1 survival; however, the offspring displayed hyperactivity of basal swimming speed in a light-to-dark behavior assessment test. These findings demonstrate that chronic exposure to PFOS adversely impacts embryonic growth, reproduction, and subsequent offspring development.

Pattern recognition receptors and genetic risk for rsv infection: value for clinical decision-making?

Respiratory syncytial virus (RSV) causes respiratory tract infections, especially among young infants. Practically, all infants are infected during epidemics and the clinical presentation ranges from subclinical to fatal infection. Known risk factors for severe RSV infection include prematurity, age of <2 months, underlying chronic lung or heart diseases, serious neurological or metabolic disorders, immune deficiency (especially a disorder of cellular immunity), crowded living conditions, and indoor smoke pollution. Twin studies indicate that host genetic factors affect susceptibility to severe RSV infection. Pattern recognition receptors (PRRs) are the key mediators of the innate immune response to RSV. In the distal respiratory tract, RSV is recognized by the transmembrane Toll-like receptor 4 (TLR4) and adapter proteins, which lead to production of proinflammatory cytokines and subsequent activation of the adaptive immune response. Surfactant proteins A and D are able to bind both RSV and TLR4, modulating the inflammatory response. Genetic variations in TLR4, SP-A, and SP-D have been associated with the risk of severe RSV bronchiolitis, but the results have varied between studies. Both the homozygous hyporesponsive 299Gly genotype of TLR4 and the non-synonymous SP-A and SP-D polymorphism influence the presentation of RSV infection. The reported relative risks associated with these markers are not robust enough to justify clinical use. However, current evidence indicates that innate immune responses including pattern recognition receptors (PRRs) and other components in the distal airways and airspaces profoundly influence the innate immune responses, playing a key role in host resistance to RSV in young infants. This information is useful in guiding efforts to develop better means to identify the high-risk infants and to treat this potentially fatal infection effectively.

Exploiting cellular-developmental evolution as the scientific basis for preventive medicine

In the post-genomic era, we must make maximal use of this technological advancement to broaden our perspective on biology and medicine. Our understanding of the evolutionary process is undermined by looking at it retrospectively, perpetuating a descriptive rather than a mechanistic approach. The reintroduction of developmental biologic principles into evolutionary studies, or evo-devo, allows us to apply embryologic cell-molecular biologic principles to the mechanisms of phylogeny, obviating the artificial space and time barriers between ontogeny and phylogeny. This perspective allows us to consider the continuum between the proximate and ultimate causes of speciation, which was unthinkable when looked at from the descriptive perspective. Using a cell-cell interactive 'middle-out' approach, we have gained insight to the evolution of the lung from the swim bladder of fish based on gene regulatory networks that generate both lung ontogeny and phylogeny, i.e. decreased alveolar size, decreased alveolar wall thickness, and increased alveolar wall strength. Vertical integration of cell-cell interactions predicts the adaptivity and maladaptivity of the lung, leading to novel insights for chronic lung disease. Since we have employed principles involved in all of development, this approach is amenable to all biologic structures, functions, adaptations, maladaptations, and diseases, providing an operational basis for preventive medicine.

Characterization of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare (Schultz), and the effect of exposure to methylene blue

Failure to inflate the swim bladder is regarded a major obstacle in the rearing of many fish species. We present a study of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare. A normal developing primordial swim bladder was first discernable at the end of the first day post-hatch (p.h.) as a cluster of epithelial cells with a central lumen, surrounded by presumably mesenchymal cells. Initial inflation occurred on the fourth day p.h. Prior to inflation the swim bladder epithelium consisted of an outer squamous and inner columnar layer. Cells of the inner layer were filled at their basal region with an amorphous material, which disappeared upon inflation. A pneumatic duct was absent, and larvae presented no need to reach the water surface for inflation, suggesting that angelfish are pure physoclists. A model for the role of the amorphous material in normal initial inflation is proposed. Abnormal swim bladders were apparent from the fourth day p.h., and methylene blue (MB) at a concentration of 5 ppm significantly increased the prevalence of SBN. Histologically, abnormal swim bladders in larvae hatched in 5 ppm MB could not be distinguished from those in fish raised under routine conditions (0.5 ppm MB). We suggest that MB may have a teratogenic effect in angelfish.

Evolution of the lung surfactant proteins in birds and mammals

Phylogenetic analyses of the families of mammalian lung surfactant proteins (SP-A, SP-B, SP-C, and SP-D) supported the hypothesis that these proteins have diverged between birds and mammals as a result of lineage-specific gene duplications and deletions. Homologs of mammalian genes encoding SP-B, SP-C, and SP-D appear to have been deleted in chickens, whereas there was evidence of avian-specific duplications of the genes encoding SP-A and presaposin. Analysis of the genes closely linked to human SP-B, SP-C, and SP-D genes revealed that all three of these genes are closely linked to genes having orthologs on chicken chromosome 6 and also to genes lacking chicken orthologs. These relationships suggest that all of the lung surfactant protein genes, as well as certain related genes, may have been linked in the ancestor of humans and chickens. Further, they imply that the loss of surfactant protein genes in the avian lineages formed part of major genomic rearrangement events that involved the loss of other genes as well.