Maternal-Fetal Oxygen Transfer in Lower Vertebrates

There exists a difference in oxygen affinity between fetal andmaternal bloods in almost all vertebrates examined and thisdifference in affinities probably facilitates oxygen transferto the fetus. It is likely that the high oxygen affinity offetal blood represents a biochemical pre-adaptation from anancestral oviparous embryo for oxygen uptake in a relativelyhypoxic environment. In most cases, the maternal-fetal differencein blood oxygen affinities is due to the characteristics ofthe fetal red cell and not due to any changes in the adult redcell during pregnancy. These characteristics are based on thepresence of a unique fetal hemoglobin with an intrinsicallyhigh affinity for oxygen or on the absence of high red cellconcentrations of organic phosphates—allosteric modulatorsof hemoglobin function. However, in several species of snake,representing different families, it appears that pregnancy isassociated with apronounced decrease in the oxygen affinityof the adult red cell. This suggests that the blood of the pregnantfemale is better able to unload oxygen to the fetus than couldthe blood of thenonpregnant adult. The maternal-fetal differencein blood oxygen affinities in these species isprobably due tothe characteristics of the fetal red cell as well as to thechange in the affinity of the adult cell during pregnancy. Nonetheless,although the magnitude of the pregnancy-associated change inoxygen affinity of the adult cell in these snakes suggests thatit is physiologically significant, the actual significance remainsto be determined.     

Chronophysiology of Prolactin in the Lower Vertebrates

In every instance tested, responses to prolactin in fish, frogs,lizards, birds and mammals vary markedly during the day. Atcertain intervals prolactin may stimulate gains in body fatstores, whereas at other intervals it may cause fat losses.Similarly, there are specific times for gonadal prosteroidogenicand antisteroidogenic activities, augmentation of body growth,inhibition of amphibian metamorphosis, pigeon cropsac stimulation,induction of migratory restlessness, and the control of migratoryorientation. Prolactin interacts with other hormones in severalways depending on their temporal relations. Changing relationsbetween the daily rhythms of prolactin and the corticosteroidrhythms are thought to control the orderly and coordinated sequencesof physiological and behavioral conditions during the annualcycle and in development.     

Cutaneous Exchange of Ions in Lower Vertebrates

SYNOPSIS. Cutaneous ion transport has long been studied forits role in osmotic and ionic regulation in amphibians. In additionto this role, it is becoming clear that cutaneous ion exchangeinfluences, and is influenced by, a number of other physiologicaland morphological factors. The exchange of Na^$ and Cl^–across the skin of larval Ambystoma tigrinum is clearly involvedin acid-base balance. The animals require NaCl in their bathingmedia in order to compensate for a respiratory acidosis or torecover normally from a metabolic acidosis. Conversely, Na^$influx is stimulated and Cl^– influx is inhibited duringhypercapnia. Cutaneous ion transport in larval A. tigrinum appearsto be at least partially influenced by cutaneous circulationas immersion in isosmotic media to reduce skin blood flow alsoslows Na^$ influx. Allometric analysis of Na^$ influx yieldeda slope of 0.52, which is significantly less than the slopepredicted for surface area. The lower slope for ion transportmay reflect changes in capillary recruitment, skin thicknessor distribution of ion transporters over the skin. In additionto the well known cutaneous ion transport of amphibians, a numberof fish and reptilian species have also been discovered to exchangeions across skin in ways which may have homeostatic consequences.     

Integumentary Effects of Prolactin in the Lower Vertebrates

Prolactin was first known as a stimulator of mammary secretion.It has since been found to induce secretion in the sebaceousglands of the mammal as well. It likewise stimulates secretoryactivity in the avian cropsac and in the mucous glands of fishesand of amphibians when thyroid hormone is also present. Prolactinhas mitogenetic effects on a variety of structures includingthe amphibian stratum corneum and induces growth of the tailfin in larval anurans and in both larval and adult newts. Prolactincauses the regression of cornified tubercles in the skin ofthe newt yetsynergizes with androgen in the presence of thethyroid hormone to induce the formation of keratinized nuptialpads. A similar synergism between prolactin and steroidal hormonesproduces avian incubation patches. There is indication thatprolactin may facilitate the growth of hair in mammals but detailedinformation is lacking. Effects on pigmentation are attributedto prolactin in two fishes.     

Evolution of Endocrine Regulation of Metamorphosis in Lower Vertebrates

Metamorphosis commonly occurs in lower vertebrates, but itsendocrine regulation is not well known outside of the Amphibia.Paedomorphosis (progenesis and neoteny) is a frequent occurrenceas well. The only endocrine-related hypothesis is that of Etkinfor amphibians. This hypothesis has been modified to accommodatesome of the recent findings, but other data have not been incorporatedand still other parts remain untested. Presumably, the hypothesisrelies entirely on endogeneous factors, and the importance ofexternal factors needs to be examined. Facultative neotenicamphibians may be useful animals for testing certain aspectsof the Etkin hypothesis. There are insufficient data for fishesat this time to evaluate the possible universality of the amphibianhypothesis.     

Evolution of Endocrine Regulation of Gastrointestinal Function in Lower Vertebrates

The information available concerning the evolution of endocrineregulation of three gastrointestinal functions in lower vertebrates—gastricacid secretion, gallbladder contraction, and pancreatic enzymesecretion—is reviewed. The actions of hormones of thecholecystokinin/gastrin family of peptides have been the mostwidely studied and are emphasized. It is concluded that regulationof pancreatic enzyme secretion is a primitive action of cholecystokininand that the sensitivity of gallbladder muscle and gastric acid-secretingcells to these peptides evolved later, possibly in the ancestrallineage that led to the gnathostomes. The need for increaseddigestive efficiency to support the higher levels of activitymade possible by the evolution of jaws is suggested as a strongselection pressure leading to this pattern of evolution of endocrineregulation of gastrointestinal function.     

Evolution of Pineal Control of Endocrine Function in Lower Vertebrates

Pineal bodies, and other associated parietal structures, areremarkably varied among vertebrates These organs apparentlyassumed, in the primitive vertebrates, a principal role in integrationof photic information. The pineal photoreceptor cell seems tohave evolved into the secretory pinealocyte that is found inmost of the higher vertebrates. Along with the evolution ofthe photoreceptor element into the pinealocyte, there is a concomitantshift in the neural connection of the pineal organ. The pinealo-fugal,sensory innervation gives way to an autonomic, pinealo-petalmotor innervation. Thus, direct photosensitivity was supercededby indirect, optically-mediated control of the now secretorypineal gland. Even though pineal organs display such unusual plasticity anddiversity across groups, responsivenses to light remains a constantfeature. Photoperiod may modify the diurnallyrhythmic patternsof melatonin secretion across seasons and invoke appropriate"programs" which permit an animal to anticipate seasonal changes.Thus, melatonin may be a key molecule, attuned to photoperiodicity,which has been selected through evolution to effect adaptationto annual events.     

Functional Evolution of Prolactin and Growth Hormone in Lower Vertebrates

Some aspects of prolactin and growth hormone biology in fishesand amphibians are considered, including the nature of the secretorycells, the regulation of their activity, the chemistry of thehormones, and their physiological activity in relation to hydromineralmetabolism and to growth and development. Inasmuch as most ofthe information is derived from only a small number of teleostand amphibian species, a broad evolutionary biology is difficultto derive without information from other fish groups especially,and a survey must be confined largely to a comparative biologyof some representative higher bony fishes with some representativeanurans and urodeles.     

Brain, Gut and Skin Peptide Hormones in Lower Vertebrates

Understanding of peptide hormone evolution rests primarily onstructural information, either direct or inferred. We summarizestudies of fishes and amphibians to provide initial informationwithin the vertebrate lineage for selected peptides which exhibitvarying structural heterogeneity. For these peptides, thyrotropin-releasinghormone, somatostatin, luteinizing hormone-releasing hormoneand cholecystokinin related peptides manifest increasing diversification.Members of these peptide families are found distributed amonga variety of tissues (e.g., brain, gut, skin, retina, sympatheticnervous system), yet the number of genes encoding for individualtypes of peptides is presently uncertain. We emphasize the needfor additional structural information, for a more thorough anddiverse taxonomic investigation within the vertebrate lineage,and for specification of those genetic elements which ultimatelydetermine evolutionary opportunities for peptide evolution.     

Na+ /H+ Exchanger in Tissues of Lower Vertebrates

Na⁺/H⁺ exchange is one of the major pathways of ion transport in cells of pro- and eukaryots and plays an important role in intracellular pH and cell volume regulation, in cell division, proliferation, as well as in epithelial transport processes. Since 1989, investigations on the molecular nature of this transporter have revealed six isoforms (NHE1–NHE6) in mammalian tissues. Most works on studies of properties of the Na/H antiporter and regulation of its activity have been carried out on mammalian tissues. This review summarizes results of studies on the Na⁺/H⁺ exchange in tissues of lower vertebrates. Of the greatest interest are investigations on the rainbow trout, whose erythrocytes were found to contain a Na⁺/H⁺ exchanger activated by catecholamines. This carrier in trout erythrocytes has been cloned and called beta-NHE ( ;NHE). Another exchanger isoform, atNHE, was isolated from the red blood cells of the giant salamander Amphiuma tridactulum. Isoforms of antiporter isolated from oocytes (XL-NHE) and renal cells of the clawed frog Xenopus laevis (XNHE) have also been described.     

Transdifferentiation Potential of Ciliary and Pigment Epithelial Cells in Lower Vertebrates and Mammals

Cellular composition of the peripheral region of the eye in amphibians and mammals as well as embryonic fissure in amphibians was studied. Different distributions of proliferating cells in retinal pigment epithelium have been revealed in adult amphibians (newt, axolotl, and Xenopus). Single cells incorporated [³H]thymidine in the newt and Xenopus; 0.4% cells, in the axolotl. An embryonic fissure was observed in the eye of the axolotl. Pigment epithelial cells in the embryonic palpebral region actively proliferated: about 20% cells incorporated [³H]thymidine. Proliferating cells were also localized in the ciliary marginal zone of the retina in all studied amphibians, particularly, in the axolotl. In newborn hamsters, [³H]thymidine-labeled cells have been revealed in the pigment epithelium as well as in the outer pigmented and inner unpigmented layers of the ciliary body. Proliferative activity of the peripheral regions of the eye is due to eye growth in adult amphibians and newborn hamsters. After retinectomy, the retina is regenerated from the cells of the growth ciliary marginal zone in all amphibians, pigment epithelial cells in the newt, and pigment epithelial cells of the embryonic fissure in the axolotl. Heterogeneous composition of the pigment epithelium in the newt and axolotl reflects high transdifferentiation potential of these regions. Structural comparison of the peripheral region of the eye in amphibians and mammals demonstrate that the ciliary body of mammals containing stem cells is homologous to the ciliary marginal zone of amphibians containing multipotent cells.     

The Latero-sensory Component of the Dermal Skeleton in Lower Vertebrates and Its Phyletic Significance

Ørvig, T. (Section of Palaeozoology, Swedish Museum of Natural History, Stockholm, Sweden.) The latero-sensory component of the dermal skeleton in lower vertebrates and its phyletic significance. Zool. Scripta 1(3–4): 139–155, 1972.–A latero-sensory component of the dermal skeleton is met with not only in teleostomian fishes, but also in arthrodires, holocephalians (the lateral line canal “rings”), some fossil selachians, bradyodonts and acanthodians, and a few, at least, of the Osteostraci. Although not yet traceable with certainty in the Heterostraci, such a component probably existed even in early stages of vertebrate history. The persistence in the adult of this component as separate ossicles embracing the lateral line canals is surely the result of regression or other modifications of the dermal skeleton in fishes like arthrodires, coelacanthids and actinopterygians, but is apparently a primitive feature in e.g. acanthodians. In discussing the phyletic relations between the latero-sensory and membranous components of the dermal skeleton, it is concluded that these probably were separate formations from the very beginning. A condition (exemplified by certain acanthodians) where separate latero-sensory ossicles of the lateral line canals are surrounded by a mosaic of small scales of membranous origin is presumably that from which the various dermal bone-patterns in lower vertebrates are all derived. A discussion is also included in this paper of the scales and otoliths in acanthodians.     

A Method for Staining Reticulum and Red Cells in Hematopoietic Tissues of Lower Vertebrates

An aqueous solution of amido black 10B with ferric ammonium sulfate was found satisfactory for staining collagen and reticular fibrils after mordant-staining with a mixture of alizarin red S-phosphomolybdic acid, tannic acid, and toiuidine blue. This staining sequence simultaneously shows reticulum, reticular cells, and red cells in fishes, and is a new procedure useful as a routine stain for hematopoietic and lymphoid organs of lower vertebrates.     

Activation of Transducin by Bistable Pigment Parapinopsin in the Pineal Organ of Lower Vertebrates

Pineal organs of lower vertebrates contain several kinds of photosensitive molecules, opsins that are suggested to be involved in different light-regulated physiological functions. We previously reported that parapinopsin is an ultraviolet (UV)-sensitive opsin that underlies hyperpolarization of the pineal photoreceptor cells of lower vertebrates to achieve pineal wavelength discrimination. Although, parapinopsin is phylogenetically close to vertebrate visual opsins, it exhibits a property similar to invertebrate visual opsins and melanopsin: the photoproduct of parapinopsin is stable and reverts to the original dark states, demonstrating the nature of bistable pigments. Therefore, it is of evolutionary interest to identify a phototransduction cascade driven by parapinopsin and to compare it with that in vertebrate visual cells. Here, we showed that parapinopsin is coupled to vertebrate visual G protein transducin in the pufferfish, zebrafish, and lamprey pineal organs. Biochemical analyses demonstrated that parapinopsins activated transducin in vitro in a light-dependent manner, similar to vertebrate visual opsins. Interestingly, transducin activation by parapinopsin was provoked and terminated by UV- and subsequent orange-lights irradiations, respectively, due to the bistable nature of parapinopsin, which could contribute to a wavelength-dependent control of a second messenger level in the cell as a unique optogenetic tool. Immunohistochemical examination revealed that parapinopsin was colocalized with Gt2 in the teleost, which possesses rod and cone types of transducin, Gt1, and Gt2. On the other hand, in the lamprey, which does not possess the Gt2 gene, in situ hybridization suggested that parapinopsin-expressing photoreceptor cells contained Gt1 type transducin GtS, indicating that lamprey parapinopsin may use GtS in place of Gt2. Because it is widely accepted that vertebrate visual opsins having a bleaching nature have evolved from non-bleaching opsins similar to parapinopsin, these results implied that ancestral bistable opsins might acquire coupling to the transducin-mediated cascade and achieve light-dependent hyperpolarizing response of the photoreceptor cells.     

Vertebrates in phylocenogenesis

Phylocenogenesis of vertebrates differs from successions and phylocenogenesis of phytocenoses in that vertebrates do not die off but only change their habitat upon transition between stages of succession. Phylocenogenesis of vertebrates is independent of that of plant communities. Changes in species composition, including speciation, that do not lead to the rearrangement of relationships in the native vertebrate community are not phytocenological events. Phylocenogenesis is initiated by the origination or invasion of life forms that are new for a given ecosystem, which leads to changes in the structure of ecological connections and redistribution of matter and energy fluxes. A phylogenetic change at the level of vertebrate community implies irreversible alteration in the composition of life forms and ecological interactions in the ecosystem.     

Specific Association of Growth-associated Protein 43 with Calcium Release Units in Skeletal Muscles of Lower Vertebrates

Growth-associated protein 43 (GAP43), is a strictly conserved protein among vertebrates implicated in neuronal development and neurite branching. Since GAP43 structure contains a calmodulin-binding domain, this protein is able to bind calmodulin and gather it nearby membrane network, thus regulating cytosolic calcium and consequently calcium-dependent intracellular events. Even if for many years GAP43 has been considered a neuronal-specific protein, evidence from different laboratories described its presence in myoblasts, myotubes and adult skeletal muscle fibers. Data from our laboratory showed that GAP43 is localized between calcium release units (CRUs) and mitochondria in mammalian skeletal muscle suggesting that, also in skeletal muscle, this protein can be a key player in calcium/calmodulin homeostasis. However, the previous studies could not clearly distinguish between a mitochondrion- or a triad-related positioning of GAP43. To solve this question, the expression and localization of GAP43 was studied in skeletal muscle of Xenopus and Zebrafish known to have triads located at the level of the Z-lines and mitochondria not closely associated with them. Western blotting and immunostaining experiments revealed the expression of GAP43 also in skeletal muscle of lower vertebrates (like amphibians and fishes), and that the protein is localized closely to the triad junction. Once more, these results and GAP43 structural features, support an involvement of the protein in the dynamic intracellular Ca²⁺ homeostasis, a common conserved role among the different species.Key words: GAP43, RyR, skeletal muscle, Xenopus, Zebrafish