Global transcriptome analysis identifies regulated transcripts and pathways activated during oogenesis and early embryogenesis in atlantic cod

Abstract

The molecular mechanisms underlying oogenesis and maternally controlled embryogenesis in fish are not fully understood, especially in marine species. Our aim was to study the egg and embryo transcriptome during oogenesis and early embryogenesis in Atlantic cod. Follicles from oogenesis stages (pre-, early-, and late-vitellogenic), ovulated eggs, and two embryonic stages (blastula, gastrula) were collected from broodstock fish and fertilized eggs. Gene expression profiles were measured in a 44 K oligo microarray consisting of 23,000 cod genes. Hundreds of differentially expressed genes (DEGs) were identified in the follicle stages investigated, implicating a continuous accumulation and degradation of polyadenylated transcripts throughout oogenesis. Very few DEGs were identified from ovulated egg to blastula, showing a more stable maternal RNA pool in early embryonic stages. The highest induction of expression was observed between blastula and gastrula, signifying the onset of zygotic transcription. During early vitellogenesis, several of the most upregulated genes are linked to nervous system signaling, suggesting increasing requirements for ovarian synaptic signaling to stimulate the rapid growth of oocytes. Highly upregulated genes during late vitellogenesis are linked to protein processing, fat metabolism, osmoregulation, and arrested meiosis. One of the genes with the highest upregulation in the ovulated egg is involved in oxidative phosphorylation, reflecting increased energy requirements during fertilization and the first rapid cell divisions of early embryogenesis. In conclusion, this study provides a large-scale presentation of the Atlantic cod's maternally controlled transcriptome in ovarian follicles through oogenesis, ovulated eggs, and early embryos. Mol. Reprod. Dev. 81: 619–635, 2014. © 2014 Wiley Periodicals, Inc.

Conserved Anti-Müllerian Hormone: Anti-Müllerian Hormone Type-2 Receptor Specific Interaction and Intracellular Signaling in Teleosts1

“…In addition, we used (A)+enriched RNA, instead of total RNA and our qPCR assay is designed to amplify a fragment from the coding region of sea bass amh (the protease cleavage region to be more precise) while in the study by García-López et al [62] primers were designed in the 3' UTR. Moreover, our results are also in line with a recent study performed on Atlantic cod showing high amh levels in follicles from pre-, early-, and late-vitellogenic stages [63]. Surprisingly, sea bass amhr2 expression levels did not follow its ligand expression trends and remained virtually invariable throughout the reproductive cycle.…”

Gene regulation of lipid and phospholipid metabolism in Atlantic cod (Gadus morhua) larvae

“…In support for this, the CTα mRNA level in the liver of rat was high before birth and decreased after birth, maybe due to reduced activity in cell division (Sesca et al, 1996). A recent study reported gene expression levels of cod eggs in 6 stages (Kleppe et al, 2014), and by analyzing their raw data (accession number E-MTAB-2170, http://www.ebi.ac.uk/arrayexpress), we found that the expression of pyct1a (ENSGAUG00000007851) was generally higher in the egg stages compared to the larvae stages (Fig. 4).…”

“…A custom, Agilent 44 k oligo microarray (A-MEXP-2226, ArrayExpress, EMBL-EBI) described by Kleppe et al (2014) was used. This microarray design is partly based on the Atlantic cod gene set described in Star et al (2011) as well as EST sequences from various cod tissues/developmental stages.…”

“…Data for egg stages refer to http://www.ebi. ac.uk/arrayexpress, accession number E-MTAB-2170 (Kleppe et al, 2014). * indicates significant different at p b 0.05 level (3 replicate for egg stages; see Appendix Table 2 for replicate number post hatch).…”

A comparison between egg trancriptomes of cod and salmon reveals species-specific traits in eggs for each species

“…To get rid of more incorrect data points, the KEGG annotations shared between cod and salmon were filtered according to a previously published protocol for salmon (Wang et al, 2014) and all probes displaying more than three hits in the salmon transcriptome was filtered away. In the cod microarray similar filtering has previously been performed, therefore none multiple transcriptome mapping sites were found for cod (Kleppe et al, 2014). This analysis left us with a total of 3,262 KEGG annotations which could be compared between species.…”