Upregulated mRNA expression of desaturase and elongase, two enzymes involved in highly unsaturated fatty acids biosynthesis pathways during follicle maturation in zebrafish.
BACKGROUND
Although unsaturated fatty acids such as eicosapentaenoic acid (EPA, C20:5n-3), docosahexaenoic acid (DHA, C22:6n-3) and arachidonic acid (ARA, C20:4n-6), collectively known as the highly unsaturated fatty acids (HUFA), play pivotal roles in vertebrate reproduction, very little is known about their synthesis in the ovary. The zebrafish (Danio rerio) display capability to synthesize all three HUFA via pathways involving desaturation and elongation of two precursors, the linoleic acid (LA, C18:2n-6) and linolenic acid (LNA, C18:3n-3). As a prerequisite to gain full understanding on the importance and regulation of ovarian HUFA synthesis, we described here the mRNA expression pattern of two enzymes; desaturase (fadsd6) and elongase (elovl5), involved in HUFA biosynthesis pathway, in different zebrafish ovarian follicle stages. Concurrently, the fatty acid profile of each follicle stage was also analyzed.


METHODS
mRNA levels of fadsd6 and elovl5 in different ovarian follicle stages were determined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. For analysis of the ovarian follicular fatty acid composition, gas chromatography was used.


RESULTS
Our results have shown that desaturase displayed significant upregulation in expression during the oocyte maturation stage. Expression of elongase was significantly highest in pre-vitellogenic follicles, followed by maturation stage. Fatty acid composition analysis of different ovarian follicle stages also showed that ARA level was significantly highest in pre-vitellogenic and matured follicles. DHA level was highest in both late vitellogenic and maturation stage.


CONCLUSIONS
Collectively, our findings seem to suggest the existence of a HUFA synthesis system, which could be responsible for the synthesis of HUFA to promote oocyte maturation and possibly ovulation processes. The many advantages of zebrafish as model system to understand folliculogenesis will be useful platform to further elucidate the regulatory and mechanism aspects of ovarian HUFA synthesis.
Ishak
Sairatul D
SD
School of Biological Sciences, Universiti Sains Malaysia, Penang. sairatul.usm@gmail.com
Tan
Sze-Huey
SH
Khong
Hou-Keat
HK
Jaya-Ram
Annette
A
Enyu
Yee-Ling
YL
Kuah
Meng-Kiat
MK
Shu-Chien
Alexander Chong
AC
D000123:Acetyltransferases / Q000096:biosynthesis*; D000818:Animals; D044943:Fatty Acid Desaturases / Q000096:biosynthesis*; D000081031:Fatty Acid Elongases; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006080:Ovarian Follicle / Q000201:enzymology / Q000254:growth & development*; D012333:RNA, Messenger / Q000378:metabolism*; D015854:Up-Regulation; D015027:Zebrafish
D012333:RNA, Messenger; D044943:Fatty Acid Desaturases; D000123:Acetyltransferases; D000081031:Fatty Acid Elongases