Читать книгу Genetic Disorders and the Fetus - Группа авторов - Страница 121

Sites of origin of colony‐forming AFCs that are not at variance with either cytokeratin findings or anatomic considerations include fetal skin, the bronchopulmonary tract, and the collecting ducts of the kidney.⁵⁸⁹ The latter site is of particular interest because kidney tissue has been implicated as a source of trisomy 20 cells,⁵⁹⁰ although trisomy 20 has also been identified in fibroblasts cultured from foreskin.⁵⁹¹ Cells staining with an antibody to glial fibrillary acidic protein (GFAP) occur in native fluids, even in the absence of NTDs, but apparently do not form proliferative colonies.⁵⁹² Enzyme expression^593–596 and morphologic resemblance to either fetal urine‐derived cells⁵⁹⁷ or amnion‐derived cells⁵⁵⁵ were the early clues to the possible sites of in vivo origin of these cells. hCG, normally produced by the placenta, appeared to be produced by AF‐type but not by F‐type cells in culture.^{571, 574–576, 576} These studies suggest that the amniotic membranes contribute to the pool of proliferating AFCs.⁵⁹⁹ Harris⁶⁰⁰ arrived at a similar conclusion based on her studies of glycoproteins secreted by AFCs.

Subsequent cytoskeleton studies contradicted these earlier findings. Regauer et al.⁵⁸⁹ found that in situ and cultivated amniotic membrane cells display a much higher cytokeratin structural complexity than any of the AF‐derived cell types, and considered the amnion an unlikely source of clonable cells. They also failed to find concordance between the cytokeratin pattern of urothelial cells and AFCs. Fetal urine cells likely also contribute to the AFC population. Several studies have shown that human fetal and postnatal urine contains cells that proliferate well in vitro.^{538, 590} Moreover, these urine‐derived clones resemble AF‐derived clones.^{597, 601} Using specific antibodies against urothelium, von Koskull et al.⁶⁰² provided results that tend to affirm the urinary origin of some types of AFCs. Although native AF at 16–18 weeks of gestation contains around 18 percent cells of colonic mucosal origin (as defined by a specific monoclonal antibody), none of the adherent cells appear to belong to this category.⁷⁶