Abstract
The primary embryonic axes in flies, frogs and fish are formed through translational regulation of localized transcripts before fertilization. In Drosophila melanogaster, the axes are established through the transport and translational regulation of gurken (grk) and bicoid (bcd) messenger RNA in the oocyte and embryo. Both transcripts are translationally silent while being localized within the oocyte along microtubules by cytoplasmic dynein. Once localized, grk is translated at the dorsoanterior of the oocyte to send a TGF-α signal to the overlying somatic cells. In contrast, bcd is translationally repressed in the oocyte until its activation in early embryos when it forms an anteroposterior morphogenetic gradient. How this differential translational regulation is achieved is not fully understood. Here, we address this question using ultrastructural analysis, super-resolution microscopy and live-cell imaging. We show that grk and bcd ribonucleoprotein (RNP) complexes associate with electron-dense bodies that lack ribosomes and contain translational repressors. These properties are characteristic of processing bodies (P bodies), which are considered to be regions of cytoplasm where decisions are made on the translation and degradation of mRNA. Endogenous grk mRNA forms dynamic RNP particles that become docked and translated at the periphery of P bodies, where we show that the translational activator Oo18 RNA-binding protein (Orb, a homologue of CEPB) and the anchoring factor Squid (Sqd) are also enriched. In contrast, an excess of grk mRNA becomes localized inside the P bodies, where endogenous bcd mRNA is localized and translationally repressed. Interestingly, bcd mRNA dissociates from P bodies in embryos following egg activation, when it is known to become translationally active. We propose a general principle of translational regulation during axis specification involving remodelling of transport RNPs and dynamic partitioning of different transcripts between the translationally active edge of P bodies and their silent core.
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🧪 Sample Preparation
💾 Data Repositories
🏛️ Research Organizations (ROR)
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📊 Figures
Figure 1
Differential association of bcd and grk with P bodies
( a - d ) mRNA detection at the dorsoanterior corner (for orientation, see Fig. 2a ) by ISH-IEM on wild-type (WT) ultra-thin frozen sections of stage 9 oocytes. ( a ) bcd mRNA (5nm, green circles) is ...
Figure 2
Dynamics of grk, bcd and Me31B particles in live oocytes
( a ) Low magnification wide-field image of the DA corner of a stage 8-9 egg chamber expressing Me31B::GFP. ( b ) Me31B::GFP expressing oocytes show small faint dynamic particles of Me31B (red arrowhe...
Figure 3
Oocyte P bodies exhibit zones differentially enriched in RNA associated proteins
( a-d,f,g ) IEM localization of RNA associated proteins in stage 9 oocytes at the DA corner. Protein in the core of the electron dense P bodies indicated by green circles, at the edge of P bodies by r...
Figure 4
RNA translation fate is regulated through association with P bodies
( a ) IEM using anti-Grk (15nm, yellow circles) on a WT stage 9 egg chamber shows Grk protein highly enriched in the tER-Golgi unit (yellow dashed box) and detected on ER (black arrowhead) at the edge...
Figure 5
RNA association with P bodies in the early embryo
( a ) Anterior region of a live early embryo expressing bcd*RFP and Me31B::GFP. The majority of bcd mRNA is detected outside of Me31B labeling, sometimes associating with the edge (arrowhead). ( b , c...
Figure images are served from the NIH/NLM PubMed Central Open Access Subset or Europe PMC; copyright remains with the publishers and authors.
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