Background Tandem mass tag spectrometry (TMT labeling-LC-MS/MS) was utilized to examine the global proteomes of Atlantic halibut eggs at the 1-cell-stage post fertilization. Comparisons were made between eggs judged to be of good quality (GQ) versus poor quality (BQ) as evidenced by their subsequent rates of survival for 12 days. Altered abundance of selected proteins in BQ eggs was confirmed by parallel reaction monitoring spectrometry (PRM-LC-MS/MS). Correspondence of protein levels to expression of related gene transcripts was examined via qPCR. Potential mitochondrial differences between GQ and BQ eggs were assessed by transmission electron microscopy (TEM) and measurements of mitochondrial DNA (mtDNA) levels. Results A total of 115 proteins were found to be differentially abundant between GQ and BQ eggs. Frequency distributions of these proteins indicated higher protein folding activity in GQ eggs compared to higher transcription and protein degradation activities in BQ eggs. BQ eggs were also significantly enriched with proteins related to mitochondrial structure and biogenesis. Quantitative differences in abundance of several proteins with parallel differences in their transcript levels were confirmed in egg samples obtained over three consecutive reproductive seasons. The observed disparities in global proteome profiles suggest impairment of protein and energy homeostasis related to unfolded protein response and mitochondrial stress in BQ eggs. TEM revealed BQ eggs to contain significantly higher numbers of mitochondria, but differences in corresponding genomic mtDNA (mt-nd5 and mt-atp6) levels were not significant. Mitochondria from BQ eggs were significantly smaller with a more irregular shape and a higher number of cristae than those from GQ eggs. Conclusion The results of this study indicate that BQ Atlantic halibut eggs are impaired at both transcription and translation levels leading to endoplasmic reticulum and mitochondrial disorders. Observation of these irregularities over three consecutive reproductive seasons in BQ eggs from females of diverse background, age and reproductive experience indicates that they are a hallmark of poor egg quality. Additional research is needed to discover when in oogenesis and under what circumstances these defects may arise. The prevalence of this suite of markers in BQ eggs of diverse vertebrate species also begs investigation.

Background: Reproductive success and normal development in all animals are dependent on egg quality and developmental competence of the produced embryo. This study employed tandem mass tags labeling based liquid chromatography tandem mass spectrometry for egg proteomic profiling to investigate differences in the global proteome of good versus poor quality Atlantic halibut eggs at 1-cell stage post fertilization. Results: A total of 115 proteins were found to be differentially abundant between good and poor quality eggs. Frequency distribution of these proteins revealed higher protein folding activity in good quality eggs in comparison to higher transcription and protein degradation activities in poor quality eggs (p < 0.05). Poor quality halibut eggs were significantly enriched with additional proteins related to mitochondrial structure and biogenesis (p < 0.05). The differential abundance of a selection of proteins was first confirmed at gene expression level using a transcriptomic approach followed by a targeted proteomic approach (parallel reaction monitoring based mass spectrometry) in biological samples obtained from two consecutive reproductive seasons. The findings of global proteome profiling, together with the validation of differential abundance of targeted proteins and their related genes, suggest impairments in protein and energy homeostasis which might be related to unfolded protein response and mitochondrial stress in poor quality eggs. Additional transmission electron microscopy studies were taken to assess potential differences in abundance and morphological integrity of mitochondria between good and poor quality eggs. Observations reveal poor quality eggs to contain significantly higher number of mitochondria with higher number of cristae. These mitochondria, however, are significantly smaller and have a more irregular shape than those found in high-quality eggs. Therewithal difference in mtDNA levels represented by mt-nd5 and mt-atp6 genomic DNA abundance in this study, were found to be not statistically significant (p > 0.05) between good and bad quality eggs at both 1 hpf and 24 hpf stages. Conclusion: Overall evidence from this study indicate that poor quality eggs undergo impairments at both transcription and translation level leading to endoplasmic reticulum and mitochondrial deficiencies. Additional research may be required to expediate the details and the potential of these impairments occurring in different species. Nonetheless, this study will pave the way for future research and will help in acceleration of recent advances in the field of embryonic developmental competence of living organisms.