Early sexual maturation – a major problem in cod farming

Hanne Johnsen defended her PhD thesis “Key genes and regulators associated with sexual differentiation and gonad development in Atlantic cod (Gadus morhua L)” on Friday February 17.

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Hanne Johnsen

Phone: +47 77 62 92 37

Early sexual maturation is a major problem in today’s cod farming. As the fish mature, energy is allocated to gonad production, hence reducing muscle growth and fillet quality. In her PhD thesis, Johnsen has studied genes and regulators associated with sexual development in Atlantic cod.

Controlling sexual maturation

In order to control sexual maturation, it is crucial to map the essential biological mechanisms involved. In this respect, Hanne Johnsen’s thesis has increased the basic knowledge about this process.

Sexual differentiation in Atlantic cod

The PhD project has identified several genes differentially regulated between male and female cod during sexual development. The PhD candidate establishes that the dmrt1 gene is central to the development of males, while the formation of estrogen in females is regulated by the cyp19a1a gene. Five different dmrt genes were found in the cod genome, and analyses of the surrounding genes in different vertebrates revealed the evolution of this gene family.

Hanne Johnsen, aged 35, is from Tromsø and completed a Master of Science degree at the Norwegian College of Fishery Science/University of Tromsø in 2006. Johnsen was then attached to the former Fiskeriforskning as a research assistant and continued as a research fellow after Fiskeriforskning became part of the food research institute Nofima.

The PhD project was mostly financed by the Research Council of Norway/Functional genomics (FUGE).

Hanne Johnsen’s supervisors during her PhD project have been senior scientists Øivind Andersen and Helge Tveiten from Nofima and Professor Jarl Bøgwald at the Norwegian College of Fishery Science/University of Tromsø.

The assessment committee comprised Professor Dan Larhammar (Dept. of Neuroscience, University of Uppsala, Sweden), Scientist Geir Lasse Taranger (Institute of Marine Research, Bergen) and Post-doctoral Research Fellow Anita Muller, Norwegian College of Fishery Science/University of Tromsø.

In addition to the published article – see link below – the following two articles form part of the thesis:

Johnsen H., Andersen Ø. “Differential expression of five dmrt genes identified in the Atlantic cod genome. The fish-specific dmrt2b diverged from dmrt2a before the fish whole-genome duplication” (Submitted to Gene).

Johnsen H., Tveiten H., Torgersen J.S., Andersen Ø. “Sexually dimorphic expression of amh and paralogs of sox9 and cyp19a in Atlantic cod (Gadus morhua L.)” (manuscript).

A link to these two articles will follow as soon as they are published.

Breeding and genetics  

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