In mouse embryos, acquisition of the nuclear lamin polypeptides A/C varies according to developmental stage and tissue type. In order to determine the precise time points and cell types in which lamin A/C are first observed, we have used two monoclonal antibodies in immunofluorescence studies of different tissues of developing mouse embryos and of young mice. One antibody (mAB346) is specific for lamins A and C, while the other (PKB8) detects lamins A, B and C. Dividing uterine development into three phases--germ layer formation, organogenesis and tissue differentiation--our results show that lamin A/C expression in the embryo proper is not observed until the third phase of development. Lamin A/C first appears at embryonic day 12 in muscle cells of the trunk, head and the appendages. Three days later it is also seen in cells of the epidermis where its appearance coincides with the time of stratification. In the simple epithelial of lung, liver, kidney and intestine, as well as in heart and brain, lamins A/C do not appear until well after birth. Embryonal carcinoma (EC) cells express lamin B but not lamin A/C. Lamin A/C expression is noted in some EC cells after they are induced to differentiate and in several differentiated teratocarcinoma cell lines. Our results suggest that commitment of a cell to a particular pathway of differentiation (assayed by cell-type-specific expression of intermediate filament proteins) usually occurs prior to the time that lamin A/C can be detected. Thus lamin A/C expression may serve as a limit on the plasticity of cells for further developmental events.
