Expression of the imprinted gene H19 in the human fetus

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Abstract
The H19 gene is a parenterally imprinted maternally expressed gene which has a pivotal role in embryogenesis and fetal development. It is tightly linked to the IGF‐II gene on chromosome 11p15.5 which is reciprocally imprinted. We studied the expression of the human H19 by in situ hybridization in an embryo 35 days post coitus (dpc) and in a fetus from the second trimester of pregnancy. The expression pattern of H19 in the human fetal tissues was similar to its expression in the mouse, and paralleled, with some exceptions, the expression of IGF‐II in human fetuses. Abundant expression was found in organs comprising the fetoplacental unit: the placenta, the fetal adrenal, and liver. The expression in the fetal adrenal cortex was most prominent in the definitive cortex and somewhat weaker in the fetal zone. Considerable expression of H19 was found in the fetal liver as early as 35 dpc and in the second trimester. Hematopoietic cells in fetal liver did not express the gene. Moderate expression of H19 was detected in the epithelium of the small intestines, in endometrial stroma and Fallopian tube. In the kidney conspicuous labeling of the metanephric blastema was noted, which was markedly reduced with differentiation to tubules. This pattern of expression is identical to that of IGF‐II in the fetal kidney and is relevant to the evolution of Wilms' tumor. No expression of H19 was found in the neural tube of the first trimester embryo or in the developing fetal brain in the second trimester, nor were transcripts detected in the choroid plexus. The localization of H19 expression within human fetal tissues may help to elucidate its role in human embryogenesis and fetal development.