Overview of Dolang sheep ovary transcriptome
The overview of Dolang sheep ovary transcriptome was same as described by
Chang et al., (2021).
Identification of DEPs in Dolang sheep ovaries using iTRAQ
Proteomics is a recently developed technology that can be used for large-scale study of protein structure and function in complex biological samples
(David et al., 2017). In this study, we employed iTRAQ technology, which is a relative proteomics quantitation method, to study differential protein expression changes in Dolang sheep ovaries during different physiological stages. Initially, we obtained 80,938 total peptides and 42,703 total proteins. In all, 4,845 ovarian proteins (out of 42,703) were identified, of which 470 were differentially expressed during estrus, dioestrus and pregnancy period. We first identified 102 up-regulated proteins and 18 down-regulated proteins in dioestrus compared to estrus ovaries. 60 proteins were up-regulated and 20 proteins were down-regulated in the luteal phase compared to pregnancy period ovaries. 24 proteins were up-regulated and 50 proteins were down-regulated during estrus compared to pregnancy period (Fig 1). Up-regulated proteins included follistatin-related protein 1 isoform X2, cleavage stimulation factor subunit 1 isoform X1, integrin alpha-M precursor, cyclin-Y-like protein 1 isoform X1 and others. Down-regulated proteins included histone H2B type 2-F, cyclin-Y isoform X1 and heat shock protein beta-6 isoform X1.
Through annotation of 3442 DEPs in the GO database, we found that 1924 DEPs were classified into biological processes category, 960 were classified into molecular function and 558 were classified into cellular components. Further analysis of DEPs clustered into biological processes revealed that 71 were related to the biological process, cellular process (52), metabolic process (52) and single-organism process (42), followed by organic substance metabolic process (41), primary metabolic process (41) and cellular metabolic process (37) (Fig 2A). In the molecular function categories, DEPs were primarily associated with molecular function and binding, indicating that proteins relating to molecular and binding functions experienced significant changes between physiological periods (Fig 2B). Cellular component ontology annotation revealed that a quarter of the DEPs belonged to cell parts and cell, followed by those belonging to the intracellular category (Fig 2C).
Lizandra et al., (2019) confirmed that a major function of small extracellular vesicles (sEVs) is to promote cellular adhesion by using iTRAQ technology and western blot. iTRAQ has also been used in studies of other animals, such as rats
(Zou et al., 2019) and canines
(Wu et al., 2018). Thus, iTRAQ technology is quite relevant in the field of proteomics research.
The KEGG pathway database is a powerful tool for analysis of gene and protein function within regulatory networks
(Kanehisa et al., 2012). In the current study, in order to identify the biological pathways associated with changes in protein expression between different-stage ovaries, all functional proteins were submitted for KEGG pathway analysis. A total of 9731 proteins were assigned to 298 KEGG pathways (Fig 3), falling into 30 main categories, including Metabolic pathways (575), Endocytosis (139), Pathways in cancer (136), the PI3K-Akt signaling pathway (120), Huntington’s disease (104), Focal adhesion (104), Spliceosome (104) and RNA transport (101). Among these 30 main categories, the metabolic pathways category included the largest number of proteins (575). These metabolic pathways included energy metabolism, carbohydrate metabolism, lipid metabolism, intracellular respiratory metabolism and amino acid metabolism, providing valuable basis for the investigation of processes underlying high prolificacy and year-round estrus. The above results were consistent with transcriptomic analysis results.
Integration of transcriptome and proteome analysis
To identify pathways associated with high prolificacy and year-round estrus in Dolang sheep for both datasets, we integrated transcriptomic and proteomic data to find the corresponding genes and proteins. We believed that there is an association when a certain identified protein is also differentially expressed at the transcriptomic level. However, we identified no intersection between transcription and protein levels based on Wayne intersection analysis of the three groups in this study. Thus, the following conjoint analysis of protein levels was not possible. In the current study, transcriptomic and proteomic data seldom overlapped, which was similar to previous reports. These differences were probably caused by differential regulation of translation, alternative splicing and database annotation errors (
Hornshøj et al., 2009).
Yang et al. (2016) analyzed the growth and development of skeletal muscle in Shaziling and Yorkshire pigs using transcriptome and proteome technology, but only three genes overlapped between transcriptomic and proteomic data.
Although transcriptomics and proteomics data had no overlap, interaction GO and KEGG pathway analyses both indicated shared important biological significance
(Kim et al., 2010). Considering this, the differentially abundant DEGs and DEPs converging in the same metabolic pathways, especially the regulation of reproductive process, were quite relevant. We found that some processes and pathways jointly play an important role in transcription and translation, as revealed by GO and KEGG pathway correlation analysis. As revealed by GO, 239 (29.7%) genes (proteins) had important roles in the biological processes of transcription and translation, corresponding to 557 (69.3%) and 8 (1%), respectively (Fig 4A). Among the 10 main entries, the biological process (GO: 0008150) included the largest number of genes and proteins (142 up-regulated, 33 down-regulated), while cellular process (GO: 0009987) was second (98 up-regulated, 22 down-regulated), followed by single-organism process (GO: 0044699, 94 up-regulated, 19 down-regulated). Processes associated with reproduction included aromatic compound biosynthetic process (GO: 0019438, 29 up-regulated, 7 down-regulated), reproductive process (GO: 0022414, 5 up-regulated, 2 down-regulated), reproduction (GO: 0000003, 4 up-regulated, 2 down-regulated), asexual reproduction (GO: 0019954, 1 up- regulated, 0 down-regulated), reproduction of a single-celled organism (GO: 0032505, 1 up-regulated, 0 down-regulated) and other pathways, which were regulated at the transcriptomic and proteomic level. KEGG pathway analysis revealed 35 (18.4%) genes (proteins) that were commonly affected, as well as 139 (73.2%) genes and 16 (8.4%) proteins with important roles in pathways at different levels (Fig 4B). Among the 35 entries, Metabolic pathways (KO 01100) included the largest number of genes (25) and proteins (20), Phagosome (KO 04145, 7 genes and 8 proteins), Glutathione metabolism (KO 00480, 5 genes and 4 proteins), Calcium signaling pathway (KO 04020
, 4 genes and 2 proteins), Thyroid hormone synthesis (KO 04918, 3 genes and 2 proteins), Endocrine and other factors-regulating calcium reabsorption (KO 04961, 2 genes and 2 proteins) and other pathways, which were regulated at both transcriptomic and proteomic level. In summary, various trends in DEP abundance were consistent with the DEG data, which revealed consistency between transcriptome sequencing results and iTRAQ proteomics analysis, suggesting that there exist important correlation between different omics data.