JEB desktop wallpaper calendar 2016

JEB desktop wallpaper calendar 2016

Control of luminescence from pygmy shark (Squaliolus aliae) photophores
Julien M. Claes, Hsuan-Ching Ho, Jérôme Mallefet

SUMMARY

The smalleye pygmy shark (Squaliolus aliae) is a dwarf pelagic shark from the Dalatiidae family that harbours thousands of tiny photophores. In this work, we studied the organisation and physiological control of these photogenic organs. Results show that they are mainly situated on the ventral side of the shark, forming a homogeneous ventral photogenic area that appears well suited for counterillumination, a well-known camouflage technique of pelagic organisms. Isolated ventral skin patches containing photophores did not respond to classical neurotransmitters and nitric oxide but produced light after melatonin (MT) application. Prolactin and α-melanocyte-stimulating hormone inhibited this hormonally induced luminescence as well as the spontaneous luminescence from the photogenic tissue. The action of MT seems to be mediated by binding to the MT2 receptor subtype, as the MT2 receptor agonist 4P-PDOT inhibited the luminescence induced by this hormone. Binding to this receptor probably decreases the intracellular cAMP concentration because forskolin inhibited spontaneous and MT-induced luminescence. In addition, a GABA inhibitory tonus seems to be present in the photogenic tissue as well, as GABA inhibited MT-induced luminescence and the application of bicuculline provoked luminescence from S. aliae photophores. Similarly to what has been found in Etmopteridae, the other luminous shark family, the main target of the luminescence control appears to be the melanophores covering the photocytes. Results suggest that bioluminescence first appeared in Dalatiidae when they adopted a pelagic style at the Cretaceous/Tertiary boundary, and was modified by Etmopteridae when they started to colonize deep-water niches and rely on this light for intraspecific behaviours.

FOOTNOTES

  • FUNDING

    Financial support was provided by an FNRS grant.

  • LIST OF SYMBOLS AND ABBREVIATIONS

    α-MSH
    α-melanocyte stimulating hormone
    BICU
    bicuculline
    5-HT
    5-hydroxytryptamin (serotonin)
    FSK
    forskolin
    GABA
    γ-aminobutyric acid
    GABAA
    GABA receptor A
    Lmax
    maximum intensity of light emission
    Ltot
    total quantity of light emitted during one experiment
    MT
    melatonin
    MT2
    melatonin receptor 2
    NO
    nitric oxide
    PC
    photogenic cover
    PD
    photophore density
    PDi
    photophore diameter
    PRL
    prolactin
    TL
    total length
    TLmax
    time elapsed from stimulation to reach Lmax
    VSP
    ventral skin patch
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