Quantitative imaging of lipids in live mouse oocytes and early embryos using CARS microscopy

Mammalian oocytes contain lipid droplets (LDs) that are a store of fatty acids, whose metabolism plays a significant role in pre-implantation development. Fluorescent staining has previously been used to image lipid droplets in mammalian oocytes and embryos, but this method is not quantitative and often incompatible with live cell imaging and subsequent development.

These data show the application of chemically specific, label-free coherent anti-Stokes Raman scattering (CARS) microscopy to mouse oocytes and pre-implantation embryos. The data show that CARS imaging can quantify the size, number and spatial distribution of lipid droplets in living mouse oocytes and embryos up to the blastocyst stage. Notably, it can be used in a way that does not compromise oocyte maturation or embryo development.

The data also correlate CARS with two-photon fluorescence microscopy simultaneously acquired using fluorescent lipid probes on fixed samples, and demonstrate only a partial degree of correlation, depending on the lipid probe, clearly exemplifying the limitation of lipid labelling.

In addition, the data show that differences in the chemical composition of lipid droplets in living oocytes matured in media supplemented with different amounts of saturated and unsaturated fatty acids can be detected using CARS hyperspectral imaging. These data demonstrate that CARS microscopy provides a novel non-invasive method of quantifying lipid content, type and spatial distribution with sub-micron resolution in living mammalian oocytes and embryos.

The data sets consists of optical microscopy images and numerical data. Microscope images show oocytes and early embryos (as cross sections in two dimensions or as maximum intensity projections), obtained using Differential Interference Contrast microscopy (DIC), CARS microscopy, and fluorescence microscopy. Lipid droplets of oocytes and early embryos are specifically visualised in the CARS microscopy images.

Numerical data consist of the following groups:

1) histogram of the occurrence of the aggregate size (number of lipid droplets per aggregate) in a representative egg. The data set is an ascii file with X and Y columns. X is the aggregate size and Y the occurrence.

2) Scatter plot of the square root of the sum of the squared aggregate size against the total number of lipid droplets, in ensembles of eggs and embryos. The data set is an ascii file with X and Y columns. X is  square root of the sum of the squared aggregate size and Y is  the total number of lipid droplets.

3) Vibrational Raman-like spectra obtained from CARS hyperspectral images of lipid droplets in representative eggs and embryos. The data set is an ascii file with X and Y columns. X is  the wavenumber and Y is CARS susceptibility (imaginary part).

4) histogram of the occurrence of the LD effective diameter in a representative egg. The data set is an ascii file with X and Y columns. X is the LD diameter and Y the occurrence.

5) Scatter plot of the diameter of LDs against the total number of LDs, in ensembles of eggs and embryos. The data set is an ascii file with X and Y columns. X is diameter of LDs and Y is the total number of lipid droplets.

Results derived from these data are published at http://dx.doi.org/10.1242/dev.129908