Are We Reaching the Limits of ?

Echoing scientific and industrial progress, the Twentieth century was an unprecedented period of improvement for human capabilities and performances, with a significant increase in lifespan, adult height, and maximal physiological performance. Analyses of historical data show a major slow down occurring in the most recent years. This triggered large and passionate debates in the academic scene within multiple disciplines; as such an observation could be interpreted as our upper biological limits.

Drastic neofunctionalization associated with evolution of the timezyme AANAT 500 Mya.

Melatonin (N-acetyl-5-methoxytrypamine) is the vertebrate hormone of the night: circulating levels at night are markedly higher than day levels. This increase is driven by precisely regulated increases in acetylation of serotonin in the pineal gland by arylalkylamine N-acetyltransferase (AANAT), the penultimate enzyme in the synthesis of melatonin. This unique essential role of AANAT in vertebrate timekeeping is recognized by the moniker the timezyme.

Somatotropic axis genes are expressed before pituitary onset during zebrafish and sea bass development.

The somatotropic axis, or growth hormone-insulin-like growth factor-1 (GH-IGF-1) axis, of fish is involved in numerous physiological process including regulation of ionic and osmotic balance, lipid, carbohydrate and protein metabolism, growth, reproduction, immune function and behavior. It is thought that GH plays a role in fish development but conflicting results have been obtained concerning the ontogeny of the somatotropic axis. Here we investigated the developmental expression of GH, GH-receptor (GHR) and IGF-1 genes and of a GH-like protein from fertilization until early stages of larval development in two Teleosts species, Danio rerio and Dicentrarchus labrax, by PCR, in situ hybridization and Western blotting.

Marine biodiversity characteristics.

Oceans contain the largest living volume of the "blue" planet, inhabited by approximately 235-250,000 described species, all groups included. They only represent some 13% of the known species on the Earth, but the marine biomasses are really huge. Marine phytoplankton alone represents half the production of organic matter on Earth while marine bacteria represent more than 10%.

Evolution of AANAT: expansion of the gene family in the cephalochordate amphioxus.

Background: The arylalkylamine N-acetyltransferase (AANAT) family is divided into structurally distinct vertebrate and non-vertebrate groups. Expression of vertebrate AANATs is limited primarily to the pineal gland and retina, where it plays a role in controlling the circadian rhythm in melatonin synthesis. Based on the role melatonin plays in biological timing, AANAT has been given the moniker "the Timezyme".

The timing of the shrew: continuous melatonin treatment maintains youthful rhythmic activity in aging Crocidura russula.

Background: Laboratory conditions nullify the extrinsic factors that determine the wild expected lifespan and release the intrinsic or potential lifespan. Thus, wild animals reared in a laboratory often show an increased lifespan, and consequently an increased senescence phase. Senescence is associated with a broad suite of physiological changes, including a decreased responsiveness of the circadian system.

Structural and functional evolution of the pineal melatonin system in vertebrates.

In most species daily rhythms are synchronized by the photoperiodic cycle. They are generated by the circadian system, which is made of a pacemaker, an entrainment pathway to this clock, and one or more output signals. In vertebrates, melatonin produced by the pineal organ is one of these outputs.

Cloning and retinal expression of melatonin receptors in the European sea bass, Dicentrarchus labrax.

Melatonin contributes to synchronizing behaviors and physiological functions to daily and seasonal rhythm in fish. However, no coherent vision emerges because the effects vary with the species, sex, age, moment of the year or sexual cycle. And, scarce information is available concerning the melatonin receptors, which is crucial to our understanding of the role melatonin plays.

[Melatonin and neuroendocrine regulations in fish].

Melatonin is the time-keeping molecule of the organism. The production by the pineal organ is responsible for the diurnal and annual rhythms of plasma melatonin content. This contributes to synchronizing behavioural, biochemical and physiological processes to the environmental variations in photoperiod and temperature.

[Photoperiodic control of melatonin synthesis in fish pineal and retina].

Melatonin is the time-keeping molecule of vertebrates. The daily and annual variations of its rhythmic production allow synchronizing physiological functions and behaviours to the variations of the environment. In fish, melatonin is produced by the photoreceptor cells of the retina and pineal organ.

Cloning and early expression pattern of two melatonin biosynthesis enzymes in the turbot (Scophthalmus maximus).

Melatonin biosynthesis from serotonin involves the sequential activation of the arylalkylamine N-acetyltransferase (AANAT) and hydroxyindole-O-methyltransferase (HIOMT). Photoperiod synchronizes a daily rhythm in pineal and retinal melatonin secretion through controlling AANAT activity. Teleost fish possess two Aanat, one expressed in the retina (AANAT1) and the other expressed in the pineal gland (AANAT2).

Melatonin effects on the hypothalamo-pituitary axis in fish.

Melatonin, a hormonal output signal of vertebrate circadian clocks, contributes to synchronizing behaviors and neuroendocrine regulations with the daily and annual variations of the photoperiod. Conservation and diversity characterize the melatonin system: conservation because its pattern of production and synchronizing properties are a constant among vertebrates; and diversity because regulation of both its synthesis and modes of action have been profoundly modified during vertebrate evolution. Studies of the targets and modes of action of melatonin in fish, and their parallels in mammals, are of interest to our understanding of time-related neuroendocrine regulation and its evolution from fish to mammals, as well as for aquacultural purposes.

Retinal, pineal and diencephalic expression of frog arylalkylamine N-acetyltransferase-1.

The arylalkylamine N-acetyltransferase (AANAT) is a key enzyme in the rhythmic production of melatonin. Two Aanats are expressed in Teleost fish (Aanat1 in the retina and Aanat2 in the pineal organ) but only Aanat1 is found in tetrapods. This study reports the cloning of Aanat1 from R.

Starting the zebrafish pineal circadian clock with a single photic transition.

The issue of what starts the circadian clock ticking was addressed by studying the developmental appearance of the daily rhythm in the expression of two genes in the zebrafish pineal gland that are part of the circadian clock system. One encodes the photopigment exorhodopsin and the other the melatonin synthesizing enzyme arylalkylamine N-acetyltransferase (AANAT2). Significant daily rhythms in AANAT2 mRNA abundance were detectable for several days after fertilization in animals maintained in a normal or reversed lighting cycle providing 12 h of light and 12 h of dark.

Melatonin pathway: breaking the 'high-at-night' rule in trout retina.

Pineal melatonin synthesis increases at night in all vertebrates, due to an increase in the activity of arylalkylamine N-acetyltransferase (AANAT). Melatonin is also synthesized in the retina of some vertebrates and it is generally assumed that patterns of pineal and retinal AANAT activity and melatonin production are similar, i.e.

Preliminary observations on the spawning conditions of the European amphioxus (Branchiostoma lanceolatum) in captivity.

Members of the subphylum Cephalochordata, which include the genus Branchiostoma (i.e. amphioxus), represent the closest living invertebrate relatives of the vertebrates.