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  • Molecular and cellular changes in skin and muscle during metamorphosis of Atlantic halibut (Hippoglossus hippoglossus) are accompanied by changes in deiodinases expression
    Publication . Campinho, Marco António; Galay-Burgos, M.; Silva, Nádia; Costa, R. A.; Alves, Ricardo N.; Sweeney, Glen E.; Power, Deborah
    Flatfish metamorphosis is the most dramatic postnatal developmental event in teleosts. Thyroid hormones (TH), thyroxine (T4) and 3,3′-5′-triiodothyronine (T3) are the necessary and sufficient factors that induce and regulate flatfish metamorphosis. Most of the cellular and molecular action of TH is directed through the binding of T3 to thyroid nuclear receptors bound to promoters with consequent changes in the expression of target genes. The conversion of T4 to T3 and nuclear availability of T3 depends on the expression and activity of a family of 3 selenocysteine deiodinases that activate T4 into T3 or degrade T4 and T3.
  • Teleost metamorphosis: the role of thyroid hormone
    Publication . Campinho, Marco António
    In most teleosts, metamorphosis encompasses a dramatic post-natal developmental process where the free-swimming larvae undergo a series of morphological, cellular and physiological changes that enable the larvae to become a fully formed, albeit sexually immature, juvenile fish. In all teleosts studied to date thyroid hormones (TH) drive metamorphosis, being the necessary and sufficient factors behind this developmental transition. During metamorphosis, negative regulation of thyrotropin by thyroxine (T4) is relaxed allowing higher whole-body levels of T4 that enable specific responses at the tissue/cellular level. Higher local thyroid cellular signaling leads to cell-specific responses that bring about localized developmental events. TH orchestrate in a spatial-temporal manner all local developmental changes so that in the end a fully functional organism arises. In bilateral teleost species, the most evident metamorphic morphological change underlies a transition to a more streamlined body. In the pleuronectiform lineage (flatfishes), these metamorphic morphological changes are more dramatic. The most evident is the migration of one eye to the opposite side of the head and the symmetric pelagic larva development into an asymmetric benthic juvenile. This transition encompasses a dramatic loss of the embryonic derived dorsal-ventral and left-right axis. The embryonic dorsal-ventral axis becomes the left-right axis, whereas the embryonic left-right axis becomes, irrespectively, the dorsal-ventral axis of the juvenile animal. This event is an unparalleled morphological change in vertebrate development and a remarkable display of the capacity of TH-signaling in shaping adaptation and evolution in teleosts. Notwithstanding all this knowledge, there are still fundamental questions in teleost metamorphosis left unanswered: how the central regulation of metamorphosis is achieved and the neuroendocrine network involved is unclear; the detailed cellular and molecular events that give rise to the developmental processes occurring during teleost metamorphosis are still mostly unknown. Also in flatfish, comparatively little is still known about the developmental processes behind asymmetric development. This review summarizes the current knowledge on teleost metamorphosis and explores the gaps that still need to be challenged.
  • Molecular, cellular and histological changes in skin from a larval to an adult phenotype during bony fish metamorphosis
    Publication . Campinho, Marco António; Silva, Nadia; Sweeney, Glen E.; Power, Deborah
    Developmental models for skin exist in terrestrial and amphibious vertebrates but there is a lack of information in aquatic vertebrates. We have analysed skin epidermal development of a bony fish (teleost), the most successful group of extant vertebrates. A specific epidermal type I keratin cDNA (hhKer1), which may be a bony-fishspecific adaptation associated with the divergence of skin development (scale formation) compared with other vertebrates, has been cloned and characterized. The expression of hhKer1 and collagen 1α1 in skin taken together with the presence or absence of keratin bundle-like structures have made it possible to distinguish between larval and adult epidermal cells during skin development. The use of a flatfish with a well-defined larval to juvenile transition as a model of skin development has revealed that epidermal larval basal cells differentiate directly to epidermal adult basal cells at the climax of metamorphosis. Moreover,hhKer1 expression is downregulated at the climax of metamorphosis and is inversely correlated with increasing thyroxin levels. We suggest that, whereas early mechanisms of skin development between aquatic and terrestrial vertebrates are conserved, later mechanisms diverge.