Maternal gene expression in Atlantic halibut (Hippoglossus hippoglossus L.) and its relation to egg quality

Abstract

BackgroundThe commercial production of Atlantic halibut (Hippoglossus hippoglossus L.) suffers from a major bottleneck due to the low success of producing juveniles for on-growing. Atlantic halibut females are routinely hand-stripped and incorrect timing of stripping can result in low quality eggs due to post-ovulatory aging. Post-ovulatory aging leads to compositional changes in eggs that include maternally provided proteins and RNAs. There have been few studies of the maternally provided mRNA transcripts that control early development in commercially important fish species. The present study aimed to study maternal gene expression in Atlantic halibut and its relation to egg quality parameters including blastomere symmetry and hatching success.ResultsA maternal EST library containing 2341 sequences was constructed by suppressive subtractive hybridisation. Thirty genes were selected for expression studies; 23 novel genes and 7 genes with documented roles in early development. The expressions of twenty-one selected genes were measured by qPCR from fertilization to the 10-somite stage. Three genes were identified as strictly maternal genes that were expressed until the start of gastrulation; askopos (kop), si:dkey-30j22.9 (Tudor family member), and Tudor 5 protein (Tdrd5). The expressions of 18 genes at the 8-cell stage were correlated with egg quality parameters. The majority of genes showed either no or very minor correlations with egg quality parameter. However, two genes correlated positively with hatching success (r> 0.50, HHC00353: r = 0.58, p < 0.01; HHC01517: r = 0.56, p < 0.01) and one gene (HHC00255) was negatively correlated with the percentage of normal blastomeres (r = -0.62, p < 0.05).ConclusionsDuring this study we have related maternal levels of gene expression to hatching success in fish. Poor hatching success was not correlated with a general decrease in transcript abundance but with low transcript levels of some specific genes. Thus, the molecular mechanisms leading to low Atlantic halibut egg quality cannot be entirely explained by post-ovulatory aging.

Expression of Developmental-Stage-Specific Genes in the Gilthead Sea Bream Sparus aurata L.

“…It also has been shown that specific genes show certain patterns of RNA degradation during early development and that maternal RNA is present (Wen et al 2005;Bai et al 2007;Ferg et al 2007). Furthermore, it has been demonstrated that the sudden decrease after germinal breakdown is characteristic for maternal genes (Mommens et al 2010). Studies in fish addressing this hypothesis are however limited.…”

Transcriptome of Atlantic Cod (Gadus morhua L.) Early Embryos from Farmed and Wild Broodstocks

“…Bonnet et al (2007) showed that prohibitin 2 was negatively associated with development success in rainbow trout. In Atlantic halibut, two maternal genes (HHC00353 and HHC01517) correlated positively with hatching success and one gene (HHC00255) correlated negatively with the percentage of normal blastomeres (Mommens et al 2010). …”

“…Furthermore, maternal transcripts may also function indirectly as a source of nutrition, providing nucleotides and phosphorus during the development (Shen-Orr et al 2010). Recent studies in rainbow trout (Oncorhynchus mykiss) and Atlantic halibut (Hippoglossus hippoglossus) have shown that some maternal mRNAs are differentially expressed in eggs of varying quality (Aegerter et al 2005;Bonnet et al 2007;Mommens et al 2010). For instance, high quality eggs were characterized by higher transcript levels of nucleoplasmin, tubulin β, and insulin-growth factor 1, and lower levels of keratins 8 and 18, cathepsin Z and prostaglandin synthase 2 in rainbow trout (Aegerter et al 2005).…”

Effect of broodstock holding environment on egg quality in farmed brown trout (Salmo trutta)

“…For example, species such as Atlantic halibut (Hippoglossus hippoglossus) have considerable potential for commercial production; however, hatching rates of less than 1% continue to obstruct the growth of the industry (Norberg et al, 1991;Mommens et al, 2011). Even in families such as the Salmonidae, where there has been considerable work on culture and incubation systems, egg mortality rates of up to 50% still occur (Bromage et al, 1992;Brooks et al, 1997;Bobe and Labbe, 2010).…”