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Abstract
In the spider, determination of the dorsal-ventral body (DV) axis depends on the interplay of the dorsal morphogen encoding gene decapentaplegic (Dpp) and its antagonist, short gastrulation (sog), a gene that is involved in the correct establishment of ventral tissues. Recent work demonstrated that the forkhead domain encoding gene FoxB is involved in dorsal-ventral axis formation in spider limbs. Here, Dpp likely acts as a dorsal morphogen, and FoxB is likely in control of ventral tissues as RNAi-mediated knockdown of FoxB causes dorsalization of the limbs. In this study, we present phenotypes of FoxB knockdown that demonstrate a function in the establishment of the DV body axis. Knockdown of FoxB function leads to embryos with partially duplicated median germ bands (Duplicitas media) that are possibly the result of ectopic activation of Dpp signalling. Another class of phenotypes is characterized by unnaturally slim (dorsal-ventrally compressed) germ bands in which ventral tissue is either not formed, or is specified incorrectly, likely a result of Dpp over-activity. These results suggest that FoxB functions as an antagonist of Dpp signalling during body axis patterning, similarly as it is the case in limb development. FoxB thus represents a general player in the establishment of dorsal-ventral structures during spider ontogeny.
Highlights
The development of spiders is the subject of intensive investigation on both morphological and molecular level, with Parasteatoda tepidariorum
Hatching rates are significantly decreased in FoxB knockdown embryos suggesting severe effects of FoxB downregulation on development
Class-III embryos, which are very rare compared to the other observed phenotypes (46/3680 embryos (=1.25%)) (Supplementary Fig. S1), develop a medially duplicated germ band (Duplicitas media) (Fig. 3)
Summary
The development of spiders is the subject of intensive investigation on both morphological and molecular level, with Parasteatoda tepidariorum In the centre of this disc forms the socalled cumulus, a “primary thickening” of mesenchymal cells Holm 1952; Akiyama-Oda and Oda 2003). A portion of these cells move to the periphery of the disc. The embryo equals a closing fan, whereby the outer rim of the fan will become the anterior pole of the embryo, and the centre of the disc, the hinge of the fan, will become the posterior pole of the embryo. Holm 1952, Akiyama-Oda and Oda 2003) (Fig. 1) The lateral sides of the fan become dorsal, and the central tissue between the hinge and the periphery become the ventral midline (e.g. Holm 1952, Akiyama-Oda and Oda 2003) (Fig. 1)
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