title: Variation in embryonic mortality and maternal transcript expression among Atlantic cod (Gadus morhua) broodstock: a functional genomics study.
abstract: Early life stage mortality is an important issue for Atlantic cod aquaculture, yet the impact of the cod maternal (egg) transcriptome on egg quality and mortality during embryonic development is poorly understood. In the present work, we studied embryonic mortality and maternal transcript expression using eggs from 15 females. Total mortality at 7days post-fertilization (7 dpf, segmentation stage) was used as an indice of egg quality. A 20,000 probe (20K) microarray experiment compared the 7hours post-fertilization (7 hpf, ~2-cell stage) egg transcriptome of the two lowest quality females (>90% mortality at 7 dpf) to that of the highest quality female (~16% mortality at 7 dpf). Forty-three microarray probes were consistently differentially expressed in both low versus high quality egg comparisons (25 higher expressed in low quality eggs, and 18 higher expressed in high quality eggs). The microarray experiment also identified many immune-relevant genes [e.g. interferon (IFN) pathway genes ifngr1 and ifrd1)] that were highly expressed in eggs of all 3 females regardless of quality. Twelve of the 43 candidate egg quality-associated genes, and ifngr1, ifrd1 and irf7, were included in a qPCR study with 7 hpf eggs from all 15 females. Then, the genes that were confirmed by qPCR to be greater than 2-fold differentially expressed between 7 hpf eggs from the lowest and highest quality females (dcbld1, ddc, and acy3 more highly expressed in the 2 lowest quality females; kpna7 and hacd1 more highly expressed in the highest quality female), and the 3 IFN pathway genes, were included in a second qPCR study with unfertilized eggs. While some maternal transcripts included in these qPCR studies were associated with extremes in egg quality, there was little correlation between egg quality and gene expression when all females were considered. Both dcbld1 and ddc showed greater than 100-fold differences in transcript expression between females and were potentially influenced by family. The Atlantic cod ddc (dopa decarboxylase) complete cDNA was characterized, and has a 1461bp open reading frame encoding a 486 amino acid protein that contains all eight residues of the conserved pyridoxal 5'-phosphate binding site including the catalytic lysine. This study provides valuable new information and resources related to the Atlantic cod egg transcriptome. Some of these microarray-identified, qPCR-confirmed, Atlantic cod egg transcripts (e.g. ddc, kpna7) play important roles during embryonic development of other vertebrate species, and may have similar functions in Atlantic cod.
authors.affiliation: Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada. Electronic address: mrise@mun.ca.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Rise
authors.affiliation: Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada.
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Nash
authors.affiliation: Aquatic Research Cluster, CREAIT Network, Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada.
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Hall
authors.affiliation: Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada.
authors.forename: Marije
authors.initials: M
authors.lastname: Booman
authors.affiliation: Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada.
authors.forename: Tiago S
authors.initials: TS
authors.lastname: Hori
authors.affiliation: Fisheries and Oceans Canada, St. Andrews Biological Station, St. Andrews, NB, E5B 2L9, Canada.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Trippel
authors.affiliation: Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada.
authors.forename: A Kurt
authors.initials: AK
authors.lastname: Gamperl
mesh_terms: D000818:Animals; D005260:Female; D029941:Fish Proteins / Q000235:genetics*; D048389:Gadus morhua / Q000196:embryology* / Q000235:genetics*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D023281:Genomics; D046228:Microarray Analysis; D010063:Ovum / Q000378:metabolism
chemical_list: D029941:Fish Proteins
keywords: Atlantic cod; Early life stage mortality; Egg; Embryo; Gene expression; Interferon pathway; Microarray