Two beta-pigment-dispersing hormone (β-PDH) isoforms in the mud crab, Scylla paramamosain: Implication for regulation of ovarian maturation and a photoperiod-related daily rhythmicity

Sep 29, 2014Animal reproduction science

Two forms of a hormone in mud crabs linked to ovarian maturation and daily rhythms influenced by light cycles

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Abstract

Two isoforms of the neuropeptide pigment dispersing hormone (PDH) were cloned in the mud crab Scylla paramamosain.

Sp-β-PDH-I shows high expression levels in the eyestalk and ovary, peaking during the vitellogenic stage and decreasing in maturity.
Sp-β-PDH-II is exclusively found in the eyestalk and has high expression only during the vitellogenic stage, with lower levels in other stages.
Daily expression analysis reveals that Sp-β-PDH-II displays a rhythmic pattern over a 24-hour period, influenced by light conditions.
Bright light exposure significantly inhibits the expression of both Sp-β-PDH isoforms.
The findings indicate that PDH may play a role in ovarian maturation regulation and suggest a connection between photoperiods and PDH expression in juvenile crabs.

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In crustaceans, the neuropeptide pigment dispersing hormone (PDH), including α- and β-PDH, is mainly involved in color changes related to the dispersion of integumental pigments and shielding pigments in the compound eye. In this study, we cloned two β-PDH isoforms in the mud crab Scylla paramamosain (termed Sp-β-PDH-I and II, respectively). The tissue distribution analysis in the females showed that Sp-β-PDH-I was mainly expressed in the eyestalk and to a much lesser extent in the brain, thoracic ganglion and ovary; however, Sp-β-PDH-II was exclusively distributed in the eyestalk. From there, we detected Sp-β-PDHs expression levels in the eyestalks (for Sp-β-PDH-I and II) and ovaries (for Sp-β-PDH-I) at different stages of ovarian development. The expression of Sp-β-PDH-I was consistent between the eyestalk and ovary; it maintained high levels from the pre-vitellogenic stage to the vitellogenic stage and then decreased significantly during the mature stage. By contrast, Sp-β-PDH-II expression levels were high only during the vitellogenic stage and significantly lower during the pre-vitellogenic and mature stages. Additionally daily expression analysis of the first stage crabs during the 24-h period showed that the expression level of Sp-β-PDH-II had an obvious daily rhythmicity and bright light could inhibit Sp-β-PDHs expressions. Moreover, photoresponses of Sp-β-PDHs further indicated that the daily rhythmicity was closely regulated by photoperiods. The combined results suggested for the first time that PDH is involved in regulating ovarian maturation in crustaceans and that a photoperiod-related daily rhythmicity of PDH exists in the juvenile crabs.

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