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      Effects of Melatonin on Anterior Pituitary Plasticity: A Comparison Between Mammals and Teleosts

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          Abstract

          Melatonin is a key hormone involved in the photoperiodic signaling pathway. In both teleosts and mammals, melatonin produced in the pineal gland at night is released into the blood and cerebrospinal fluid, providing rhythmic information to the whole organism. Melatonin acts via specific receptors, allowing the synchronization of daily and annual physiological rhythms to environmental conditions. The pituitary gland, which produces several hormones involved in a variety of physiological processes such as growth, metabolism, stress and reproduction, is an important target of melatonin. Melatonin modulates pituitary cellular activities, adjusting the synthesis and release of the different pituitary hormones to the functional demands, which changes during the day, seasons and life stages. It is, however, not always clear whether melatonin acts directly or indirectly on the pituitary. Indeed, melatonin also acts both upstream, on brain centers that control the pituitary hormone production and release, as well as downstream, on the tissues targeted by the pituitary hormones, which provide positive and negative feedback to the pituitary gland. In this review, we describe the known pathways through which melatonin modulates anterior pituitary hormonal production, distinguishing indirect effects mediated by brain centers from direct effects on the anterior pituitary. We also highlight similarities and differences between teleosts and mammals, drawing attention to knowledge gaps, and suggesting aims for future research.

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          Most cited references213

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          The amphioxus genome and the evolution of the chordate karyotype.

          Lancelets ('amphioxus') are the modern survivors of an ancient chordate lineage, with a fossil record dating back to the Cambrian period. Here we describe the structure and gene content of the highly polymorphic approximately 520-megabase genome of the Florida lancelet Branchiostoma floridae, and analyse it in the context of chordate evolution. Whole-genome comparisons illuminate the murky relationships among the three chordate groups (tunicates, lancelets and vertebrates), and allow not only reconstruction of the gene complement of the last common chordate ancestor but also partial reconstruction of its genomic organization, as well as a description of two genome-wide duplications and subsequent reorganizations in the vertebrate lineage. These genome-scale events shaped the vertebrate genome and provided additional genetic variation for exploitation during vertebrate evolution.
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            Zebrafish hox clusters and vertebrate genome evolution.

            HOX genes specify cell fate in the anterior-posterior axis of animal embryos. Invertebrate chordates have one HOX cluster, but mammals have four, suggesting that cluster duplication facilitated the evolution of vertebrate body plans. This report shows that zebrafish have seven hox clusters. Phylogenetic analysis and genetic mapping suggest a chromosome doubling event, probably by whole genome duplication, after the divergence of ray-finned and lobe-finned fishes but before the teleost radiation. Thus, teleosts, the most species-rich group of vertebrates, appear to have more copies of these developmental regulatory genes than do mammals, despite less complexity in the anterior-posterior axis.
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              Prolactin: structure, function, and regulation of secretion.

              Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.
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                Author and article information

                Contributors
                Journal
                Front Endocrinol (Lausanne)
                Front Endocrinol (Lausanne)
                Front. Endocrinol.
                Frontiers in Endocrinology
                Frontiers Media S.A.
                1664-2392
                11 January 2021
                2020
                : 11
                : 605111
                Affiliations
                [1] 1Department of Pharmacy, Faculty of Mathematics and Natural Sciences, University of Oslo , Oslo, Norway
                [2] 2Department of Oral Biology, Faculty of Dentistry, University of Oslo , Oslo, Norway
                [3] 3Physiology Unit, Faculty of Veterinary Medicine, Norwegian University of Life Sciences , Oslo, Norway
                [4] 4Laboratoire Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), MNHN, CNRS FRE 2030, SU, IRD 207, UCN, UA , Paris, France
                Author notes

                Edited by: Vance L. Trudeau, University of Ottawa, Canada

                Reviewed by: Hélène Volkoff, Memorial University of Newfoundland, Canada; Hana Zemkova, Academy of Sciences of the Czech Republic (ASCR), Czechia

                *Correspondence: Romain Fontaine, romain.fontaine@ 123456nmbu.no

                This article was submitted to Neuroendocrine Science, a section of the journal Frontiers in Endocrinology

                Article
                10.3389/fendo.2020.605111
                7831660
                33505357
                9a0fc19c-1c3e-40fb-9675-8db11f86d793
                Copyright © 2021 Ciani, Haug, Maugars, Weltzien, Falcón and Fontaine

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 11 September 2020
                : 12 November 2020
                Page count
                Figures: 5, Tables: 4, Equations: 0, References: 213, Pages: 20, Words: 10254
                Funding
                Funded by: Norges Miljø- og Biovitenskapelige Universitet 10.13039/501100008119
                Funded by: Universitetet i Oslo 10.13039/501100005366
                Categories
                Endocrinology
                Review

                Endocrinology & Diabetes
                melatonin,adenohypophysis,photoperiod,melatonin receptors,seasonal reproduction,plasticity,endocrinology,light

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