USING EXPANSION MICROSCOPY TO STUDY THE FORM AND FUNCTION OF NUCLEAR ENVELOPE INVAGINATIONS IN ZEBRAFISH EMBRYONIC DEVELOPMENT

The nuclear envelope (NE) is a structure comprised of a double membrane, pores and functional proteins, surrounding the nucleus of most eukaryotic cells.

Research found that the NE can contain invaginations, formed by folding of the nuclear membrane. Nuclear envelope invaginations (NEIs) of different morphologies have been observed in a variety of cell types (Fricker et al., 1997; Malhas et al., 2011). We discovered that NEIs also exist naturally in wildtype zebrafish embryos, and in particular, form tubular structures that fully cross embryonic cell nuclei (Freifeld et al., 2017).

It is expected the NEIs will extend the role of the NE in allowing communication between the cytosol and the nucleus and thus, e.g., regulating gene expression. However, their function is not yet known. We hypothesize that NEIs play a specific role in development. To test this, and more broadly shed light on this phenomenon, we set out to characterize the morphologies of NEIs throughout developing zebrafish embryos, and their relations to transcription activity. Due to the small size of NEIs, this requires imaging resolution beyond the diffraction limit. Thus, we use Expansion Microscopy (ExM), a super-resolution technique, that utilizes physical magnification of the specimen to increase the effective resolution of standard microscopes.

Here we will describe our preliminary results from this pursuit.

References

Freifeld, L., Odstrcil, I., Förster, D., Ramirez, A., Gagnon, J.A., Randlett, O., Costa, E.K., Asano, S., Celiker, O.T., Gao, R., et al. (2017). Expansion microscopy of zebrafish for neuroscience and developmental biology studies. Proc. Natl. Acad. Sci. 114, E10799–E10808.

Fricker, M., Hollinshead, M., White, N., and Vaux, D. (1997). Interphase nuclei of many mammalian cell types contain deep, dynamic, tubular membrane-bound invaginations of the nuclear envelope. J. Cell Biol. 136, 531–544.

Malhas, A., Goulbourne, C., and Vaux, D.J. (2011). The nucleoplasmic reticulum: form and function. Trends Cell Biol. 21, 362–373.