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Molecular investigations on sex determination and differentiation pathways in the common carp, Cyprinus carpio


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Barney, Megan Louise 2010 , 'Molecular investigations on sex determination and differentiation pathways in the common carp, Cyprinus carpio', PhD thesis, University of Tasmania.

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Common carp is a highly important species, with significant aquaculture production
and frequent use for fish biology and aquaculture research. In Australia, New
Zealand and the US, common carp are declared as an invasive pest causing damage
to endemic ecosystems. This thesis aims to advance our understanding of the
molecular pathway of sex determination and differentiation in common carp with a
view to facilitate the development of genetic control mechanisms in this species. The
objective was addressed by the molecular cloning of six key genes involved in sexual
development, 3 each critical for female and male development. Spatial expression of
these genes was analysed in adult tissues and the onset and timing of expression was
determined during early ontogeny and through larval development at two
temperatures (20 and 25 °C) allowing investigation of the effect of temperature on
expression and final sex ratios.
The study confirms that there are two isoforms of the cytochrome P450 aromatase
gene in the species, namely the ovarian (cyp19a) and brain (cyp19b). Based on the
level of CYP19 expression, the brain was found to be the main site of aromatase
synthesis, contributed predominantly by the brain isoform. Also expressed highly in
the brain were both isoforms of SRY (sex-determining region Y)-box 9 (sox9) and
forkhead box L2 (foxL2). Within the gonad, cyp19a and foxL2 were predominantly
expressed in the ovary while doublesex and mab-3 related transcription factor 1
(dmrt1) was primarily expressed in the testis. Ontogenic expression indicated that
cyp19a and sox9a were maternally inherited. Female critical cyp19a showed sexually
dimorphic expression only in fish larger than 20 mm, with warmer conditions (25 °C)
suppressing expression and suggesting a male-skewed final sex ratio. This indicates
that differential expression maybe a result of sex differentiation rather than a cause.
Conversely, expression of cyp19b peaked prior to hatching possibly indicating that
sexual differentiation occurs first in the brain, before the gonads are present.
Expression of dmrt1, critical for male development, peaked soon after fertilisation in
the 25 °C treatment indicating a role early in the sex-determining pathway. Peak
expression of sox9 genes and foxL2 occurred prior to hatch, with consequent
expression failing to show any sexually dimorphic expression, suggesting that these
genes play a role in early larval development in the species, but not sex
This thesis found cyp19a and dmrt1 to be accurate markers of either ovarian or testis
differentiation respectively. The ability to influence the expression of these genes
may result in manipulation of sex ratios of common carp, and other fish. This would
be of benefit to both pest control, where population sex bias can result in extinction,
and also aquaculture, where monosex populations can improve production efficiency.
By developing a greater understanding of sex determination and differentiation
teleost fish it is possible to gain further insights into the evolution of sex
determination in all vertebrate species.

Item Type: Thesis - PhD
Authors/Creators:Barney, Megan Louise
Copyright Holders: The Author
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No access or viewing until 31 May 2013. After that date, available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2010. Includes bibliographical references

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