Mother-Specific Signature in the Maternal Transcriptome Composition of Mature, Unfertilized Zebrafish Eggs

Abstract

Maternal mRNA present in mature oocytes plays an important role in the proper development of the early embryo. As the composition of the maternal transcriptome in general has been studied with pooled mature eggs, potential differences between individual eggs are unknown. Here we present a transcriptome study on individual zebrafish eggs from clutches of five mothers in which we focus on the differences in maternal mRNA abundance per gene between and within clutches. To minimize technical interference, we used mature, unfertilized eggs from siblings. About half of the number of analyzed genes was found to be expressed as maternal RNA. The expressed and non-expressed genes showed that maternal mRNA accumulation is a non-random process, as it is related to specific biological pathways and processes relevant in early embryogenesis. Moreover, it turned out that overall the composition of the maternal transcriptome is tightly regulated as about half of the expressed genes display a less than twofold expression range between the observed minimum and maximum expression values of a gene in the experiment. Even more, the maximum gene-expression difference within clutches is for 88% of the expressed genes lower than twofold. This means that expression differences observed in maternally expressed genes are primarily caused by differences between mothers, with only limited variability between eggs from the same mother. This was underlined by the fact that 99% of the expressed genes were found to be differentially expressed between any of the mothers in an ANOVA test. Furthermore, linking chromosome location, transcription factor binding sites, and miRNA target sites of the genes in clusters of distinct and unique mother-specific gene-expression, suggest biological relevance of the mother-specific signatures in the maternal transcriptome composition. Altogether, the maternal transcriptome composition of mature zebrafish oocytes seems to be tightly regulated with a distinct mother-specific signature.

Transcriptome Analysis of Rainbow Trout (Oncorhynchus mykiss) Eggs Subjected to the High Hydrostatic Pressure Treatment

“…This observation suggests that interindividual differences between rainbow trout females from the winter broodstock had larger influence on the egg transcriptome and developmental ability than HHP treatment of the eggs. Similar has been observed in the zebrafish ( Danio rerio ) eggs where differences in the expression of maternal genes in eggs from different clutches reflected differences between mothers [ 25 ].…”

Lost in translation: egg transcriptome reveals molecular signature to predict developmental success and novel maternal-effect genes

“…A recent paper demonstrated that the transcriptome in unfertilized zebrafish eggs from different mothers can be quite variable while it was more uniform within clutches, which suggests that mother-related differences in the transcriptome may potentially be associated with egg quality and subsequent development of the embryo[29]. To this end, we performed a couples analysis in which we compared clutches of eggs from 3 couples that consistently produced bad quality eggs to those that frequently gave good quality eggs in order to eliminate some of the environmental effects on maternal health and egg competence.…”

Expression of distinct maternal and somatic 5.8S, 18S, and 28S rRNA types during zebrafish development

“…3B-D), was determined by calculating each possible ungapped and unidirectional alignment of 5 nt or longer of the ribosomal stretch with all available 5 ′ UTRs of zebrafish RNA transcripts using the BLAST package version 2.2.29. The 5 ′ UTRs were retrieved from Ensembl BioMart and, in order to be able to compare our results with the transcriptomics set of Rauwerda et al (2016), Ensembl release version 79 was used. For each 5…”

“…Per gene, the counts were averaged and the ratio of the counts on the maternal-and somatic-type (ms-ratio) was calculated; ms-ratios in maternally expressed and nonexpressed genes were calculated using the set of expressed and nonexpressed genes from Rauwerda et al (2016). Overrepresentation of maternally expressed genes in the sets with ms-ratios smaller or larger than one was calculated with a Fisher's exact test implemented in the R stats package, while excluding genes with a ms-ratio of exactly one.…”