Fish and amphibian models for developmental endocrinology

Abstract

The hormonal control of ontogeny in fish and amphibians is reviewed. Neuroendocrine regulation and actions of metabolic and osmoregulatory hormones (thyroid, interrenal, pituitary, pancreas, and gut) during amphibian and fish metamorphosis and the parr-smolt transformation of juvenile salmon are considered. The developmental significance of hormones in egg yolk is discussed. It is concluded that the transitions between life-history stages provide many unique opportunities for studying basic endocrine phenomena.The study of hormones in ontogeny is particularly interesting and challenging because the endocrinology of the animals under investigation is continually changing through time, e.g., the embryo progresses to larva, juvenile, and adult. The transitions between life-history stages provide many unique opportunities for studying basic endocrine phenomena. For example, during development a tissue can gain or lose status as an endocrine target, and such events can be exploited to investigate mechanisms and control of cellular responses to hormones. The endocrine system not only influences and directs development, but also is itself a subject of a developmental program. Complex neuroendocrine systems evolve from simpler ones, and this can also present valuable opportunities for research. Studies in developmental endocrinology can focus on the appearance of hormones in endocrine tissue, the appearance and disappearance of hormone receptors in endocrine targets, changes in the functions of hormones during development, the ontogeny of hormone feedback mechanisms, and other regulatory processes. In contrast, endocrine studies of adult animals are usually conducted with the assumption that the basic function and control of the endocrine glands and their relationships with the target tissues are unchanging.As alternates to mammalian models, there are numerous examples in fish and amphibian ontogeny that are appealing to the endocrinologist. The best known and most utilized of these are metamorphoses. Fish and amphibian metamorphoses include many dramatic and quantifiable developmental changes that are under hormone control. The metamorphosis of the tadpole into the adult frog, and its control by thyroid hormones, have been a long-standing subject of investigation. It was perhaps the first "model" used to study hormonal control of ontogeny (Gudernatsch, '12). Generations of developmental endocrinologists have been trained with this model and its investigation continues to yield important insights into the actions, interactions, and mechanisms of action of hormones in development. Several parallels to amphibian metamorphosis and its hormonal control occur in fish, including flounder metamorphosis and the parr-smolt transformation of migratory salmonids. The more recent investigations of fish and amphibians emphasize the multihormonal nature of developmental control mechanisms.With respect to the earliest stages of development, fish and amphibians have been less well studied. Thyroid hormones have long been known t...

Quantitative Trait Loci × Maternal Cytoplasmic Environment Interaction for Development Rate in Oncorhynchus mykiss

“…Maternal corticosteriods have been shown to affect growth rate pulses in damselfish prior to hatching (McCormick and Nechaev 2002), but this study and a study in coho salmon (Stratholt et al 1997) did not find differences in hatching time or development rate as a result of maternal corticosteroids. Maternal thyroid hormones in eggs have long been known for their role in growth and metamorphosis in teleosts and other vertebrate animals (Dickhoff et al 1990 and references therein). In rainbow trout, maternal mRNA has been shown to direct the progression of embryonic development until gastrulation when transcription of the embryonic nuclear genome begins (Nagler 2000).…”

Maternal Thyroid and Glucocorticoid Hormone Interactions in Larval Fish Development, and Their Applications in Aquaculture

“…A possible significance of THs in early fish growth and development was implied by the acute responsiveness of very young fish to antithyroid drugs and hormone supplementation treatments (reviewed by Youson, 1988;Brown and Bern, 1989;Dickhoff et al, 1990). The sensitivity of newly hatched fish to THs was reported by Lam and others who found that T 4 treatment accelerated development and larval metamorphosis, and increased survival rates (Lam, 1980;Lam, 1985;Lam and Sharma, 1985).…”

L'argenture de l'Anguille : métamorphose, anticipation, adaptation

“…On connaît le rôle majeur des hormones thyroïdiennes dans la métamorphose des amphibiens. Au cours de cette dernière, des pics plasmatiques successifs de thyroxine, de cortisone et de prolactine (PRL) ont été mis en évidence chez Rana catesbeiana (DICKHOFF et al, 1990). Une augmentation, dans l'hypophyse, de la sous-unité a des hormones glycoprotéiques (TANAKA et al, 1991) et des ARN messagers codant pour l'hormone de croissance (TAKAHASHI et al, 1992) a également été démontrée.…”

“…Il s'agit, comme pour l'argenture, de l'expression d'adaptats anticipateurs qui prépare le poisson, en eau douce, à sa migration marine. Au cours de la transformation du parr en smolt, des pics plasmatiques successifs d'insuline, de prolactine, de T3 et de T4, d'hormone de croissance et de Cortisol ont été mis en évidence (DICKHOFF et al, 1990 ;BOEUF, 1993). Des travaux effectués sur les Salmonidés, au cours de l'accommodation à l'eau de mer, nous renseignent de plus sur certains des effets de ces hormones.…”