Annexin A7 immunoreactivity in early mouse embryos. (A) Phase contrast, embryo E5: The egg cylinder consists of an inner cell mass (a) representing the ectoderm and an outer layer of endoderm cells (b). (B) Immunostaining of the paraffin section was performed using purified mAb 203–217 and Cy3-conjugated anti-mouse IgG. Annexin A7 is expressed in both cell types of the egg cylinder with a strong staining of the endoderm and a weaker staining of the ectoderm. The nuclei are devoid of immune reactions. (C) Negative control using the secondary Cy3-antibody only. (D-F) Annexin A7 expression in the proximal neural tube (D) and nearby neural fold (E,F), embryo E8, transverse section. Immunolabeling of Annexin A7 was performed with purified mAb 203–217 and visualization was with an Alexa Fluor 488-conjugated anti-mouse IgG. (D) An intense Annexin A7 immunostaining is detectable in the neuroepithelium of the neural tube (a, lumen of neural tube). (E,F) Higher magnifications of the neuroepithelium show that Annexin A7 is expressed in the cytosol. Arrowheads point to Annexin A7 immunoreactivity in the cytosol. (G) Phase contrast, embryo E13, caudal neural tube. (H) Immunostaining of the paraffin section was performed using purified mAb 203–217 and Alexa Fluor 488-conjugated anti-mouse IgG. (I) Negative control using the secondary Alexa Fluor 488-antibody only. Bar, 20 μm.