Project description:microRNAs (miRNAs) are important regulators of animal development and other processes, and impart robustness to living systems through post-transcriptional regulation of specific mRNA transcripts. It is postulated that newly emergent miRNAs are generally expressed at low levels and with spatiotemporally restricted expression domains, thus minimising effects of spurious targeting on animal transcriptomes. Here we present ovarian miRNA transcriptome data for two geographically distinct populations of the Speckled Wood butterfly (Pararge aegeria). A total of 74 miRNAs were identified, including 11 newly discovered and evolutionarily-young miRNAs, bringing the total of miRNA genes known from P. aegeria up to 150. We find a positive correlation between miRNA age and expression level. A common set of 55 miRNAs are expressed in both populations. From this set, we identify seven that are consistently either ovary-specific or highly upregulated in ovaries relative to other tissues. This ovary set includes miRNAs with known contributions to ovarian function in other insect species with similar ovaries and mode of oogenesis, including miR-989 and miR-2763, plus new candidates for ovarian function. We also note that conserved miRNAs are overrepresented in the ovary relative to the whole body.
Project description:microRNAs (miRNAs) are important regulators of animal development and other processes, and impart robustness to living systems through post-transcriptional regulation of specific mRNA transcripts. It is postulated that newly emergent miRNAs are generally expressed at low levels and with spatiotemporally restricted expression domains, thus minimising effects of spurious targeting on animal transcriptomes. Here we present ovarian miRNA transcriptome data for two geographically distinct populations of the Speckled Wood butterfly (Pararge aegeria). A total of 74 miRNAs were identified, including 11 newly discovered and evolutionarily-young miRNAs, bringing the total of miRNA genes known from P. aegeria up to 150. We find a positive correlation between miRNA age and expression level. A common set of 55 miRNAs are expressed in both populations. From this set, we identify seven that are consistently either ovary-specific or highly upregulated in ovaries relative to other tissues. This 'ovary set' includes miRNAs with known contributions to ovarian function in other insect species with similar ovaries and mode of oogenesis, including miR-989 and miR-2763, plus new candidates for ovarian function. We also note that conserved miRNAs are overrepresented in the ovary relative to the whole body.
Project description:The maternal effect genes responsible for patterning the embryo along the antero-posterior (AP) axis are broadly conserved in insects. The precise function of these maternal effect genes is the result of the localisation of their mRNA in the oocyte. The main developmental mechanisms involved have been elucidated in Drosophila melanogaster, but recent studies have shown that other insect orders often diverge in RNA localisation patterns. A recent study has shown that in the butterfly Pararge aegeria the distinction between blastodermal embryonic (i.e. germ band) and extra-embryonic tissue (i.e. serosa) is already specified in the oocyte during oogenesis in the ovariole, long before blastoderm cellularisation. To examine the extent by which a female butterfly specifies and patterns the AP axis within the region fated to be the germ band, and whether she specifies a germ plasm, we performed in situ hybridisation experiments on oocytes in P. aegeria ovarioles and on early embryos. RNA localisation of the following key maternal effect genes were investigated: caudal (cad), orthodenticle (otd), hunchback (hb) and four nanos (nos) paralogs, as well as TDRD7 a gene containing a key functional domain (OST-HTH/LOTUS) shared with oskar. TDRD7 was mainly confined to the follicle cells, whilst hb was exclusively zygotically transcribed. RNA of some of the nos paralogs, otd and cad revealed complex localisation patterns within the cortical region prefiguring the germ band (i.e. germ cortex). Rather interestingly, otd was localised within and outside the anterior of the germ cortex. Transcripts of nos-O formed a distinct granular ring in the middle of the germ cortex possibly prefiguring the region where germline stem cells form. These butterfly RNA localisation patterns are highly divergent with respect to other insects, highlighting the diverse ways in which different insect orders maternally regulate early embryogenesis of their offspring.
Project description:MicroRNAs (miRNAs) are involved in post-transcriptional regulation of gene expression. Since several miRNAs are known to affect the stability or translation of developmental regulatory genes, the origin of novel miRNAs may have contributed to the evolution of developmental processes and morphology. Lepidoptera (butterflies and moths) is a species-rich clade with a well-established phylogeny and abundant genomic resources, thereby representing an ideal system in which to study miRNA evolution. We sequenced small RNA libraries from developmental stages of two divergent lepidopterans, Cameraria ohridella (Horse chestnut Leafminer) and Pararge aegeria (Speckled Wood butterfly), discovering 90 and 81 conserved miRNAs respectively, and many species-specific miRNA sequences. Mapping miRNAs onto the lepidopteran phylogeny reveals rapid miRNA turnover and an episode of miRNA fixation early in lepidopteran evolution, implying that miRNA acquisition accompanied the early radiation of the Lepidoptera. One lepidopteran-specific miRNA gene, miR-2768, is located within an intron of the homeobox gene invected, involved in insect segmental and wing patterning. We identified cubitus interruptus (ci) as a likely direct target of miR-2768, and validated this suppression using a luciferase assay system. We propose a model by which miR-2768 modulates expression of ci in the segmentation pathway and in patterning of lepidopteran wing primordia. Examination of the small RNA complements pooled across life cycle stages in each of Cameraria ohridella and Pararge aegeria.