Anteroposterior axis determination in pea aphid Acyrthosiphon pisum
Date Issued
2010
Date
2010
Author(s)
Huang, Ting-Yu
Abstract
Patterning insect embryos is controlled by a spectrum of well-conserved genes. Anteroposterior axis formation is well understood in Drosophila in which bicoid and caudal encode proteins that form morphogenetic gradients from both poles of the embryo and both of them play a key role in anterior and posterior patterning of the fruit fly embryo. However, recent studies suggest bicoid is an invention of new regulatory protein during the evolution. In some non-dipteran insects such as wasp (Nasonia vitripennis) and beetle (Tribolium castaneum), the anterior specification relies on a synergistic interaction between hunchback and orthodenticle.
Evidence shown here indicates it is the asymmetric localization of Aphb rather than the synergistic interaction between Aphb and Apotd, which regulate the anterior development in the asexual pea aphid. Furthermore, unlike Drosophila caudal which forms a linear concentration gradient in early embryogenesis, Apcad does not show a gradient expression in early developmental stages. But, Apcad transcript is expressed in the posteriormost of the germ band in mid- and late- embryogenesis, and might involve in the germ cell formation in the pea aphid. In conclusion, Aphb, Apotd and Apcad exhibit some conserved features in later embryogenesis in the pea aphid as well as in other insects; however, they diverse in early oogenesis and embryogenesis.
Compared to Drosophila which patterns most of its segments in syncytial blastoderm stage, most arthropods generate its segments from a celluarized environment. Here, three conserved segment polarity genes, engrailed-1, engrailed-2 and wingless have been cloned and illustrated the expression of their transcripts. It is shown that the first appearing segment is the third segment of thorax (T3), and then remaining segments add from head to abdomen sequentially. The expression of Apwg is also shown periodically and co-localized with Apcad transcript in the posterior of the germ band. It suggests that the segmentation mechanism in pea aphid might be conserved, similar to other short germ band insects. However, the possible regulation between genes which involve in axis formation (Aphb, Apotd, and Apcad) and genes which involve in segment formation (Apen-1, Apen-2, and Apwg) remains unclear and worthy of further investigation.
Subjects
pea aphid
axis determination
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