Molecular structural changes in human fetal tissue during the early stages of embryogenesis.

Low-angle synchrotron X-ray diffraction studies of human fetal extensor tendon and skin collagen, centred in time about the period of first major movement by the fetus, indicate that alignment of the tendon collagen fibrils occurs about this time. At this stage there appears to be no detectable structural difference between tendon and dermis. By three weeks post-partum, marked differences between these tissues can be detected. The distribution of the intermediate filament diameters for all fetal tendons investigated was unimodal (mean 41.2 +/- 0.4 nm) in contrast with that for post-partum tendon which is multimodal. Equatorial periodicities of 353 +/- 3 nm and 32.1 +/- 0.1 nm, consistent with the presence of type IV collagen, were obtained from all fetal samples examined. Neither of these periodicities were observed in post-partum normal tendon and only the larger were observed in post-partum normal skin. The consistency of the results suggest that low-angle X-ray diffraction could be used for the identification of fetal-like tissues found in pathological tissues.