Date Published: May 2, 2019
Publisher: Public Library of Science
Author(s): Keiji Itoh, Alice H. Reis, Andrew Hayhurst, Sergei Y. Sokol, Michael Klymkowsky.
The use of Xenopus laevis as a model for vertebrate developmental biology is limited by a lack of antibodies specific for embryonic antigens. This study evaluated the use of immune and non-immune phage display libraries for the isolation of single domain antibodies, or nanobodies, with specificities for Xenopus embryonic antigens. The immune nanobody library was derived from peripheral blood lymphocyte RNA obtained from a llama immunized with Xenopus gastrula homogenates. Screening this library by immunostaining of embryonic tissues with pooled periplasmic material and sib-selection led to the isolation of several monoclonal phages reactive with the cytoplasm and nuclei of gastrula cells. One antigen recognized by a group of nanobodies was identified using a reverse proteomics approach as nucleoplasmin, an abundant histone chaperone. As an alternative strategy, a semi-synthetic non-immune llama nanobody phage display library was panned on highly purified Xenopus proteins. This proof-of-principle approach isolated monoclonal nanobodies that specifically bind Nuclear distribution element-like 1 (Ndel1) in multiple immunoassays. Our results suggest that immune and non-immune phage display screens on crude and purified embryonic antigens can efficiently identify nanobodies useful to the Xenopus developmental biology community.
For several decades, Xenopus laevis embryos have been a leading non-mammalian model for vertebrate embryology. Major advances have been made using this model, including the discoveries of nuclear reprogramming , localized maternal RNAs , key cell cycle components  and signaling factors mediating mesoderm and neural tissue induction [4–8]. Despite these achievements, lack of antibodies specific to embryo components remains a major challenge impeding further progress of molecular and cell biological studies using Xenopus.