Vascular and mesenchymal factors during heart development: a chronological study

As heart development is an incomplete described area, and likewise an important source of intra- and post-partum morbidity and mortality, we have aimed at analyzing both vascular and cytoskeletal factors during early heart development in humans. The distribution of CD105, CD31, α-SMA, vimentin and desmin have been studied on a series of normal human heart tissues varying between five and 33 weeks of gestational age, utilizing both enzymatic single immunohistochemistry, as well as double immunofluorescence. We showed here that CD105 is already expressed at five weeks of gestational age in the future endocardium, and that between 9 and 10 weeks it shows clear-cut formed vessels. CD31 was also present diffusely at five weeks in the myocardium, while beginning with seven weeks, endocardium and vessels were clearly positive. Contrary to what it might be expected for striated muscle cells, cardiomyocytes were α-SMA positive between 9 and 20 weeks, a time window during which the marker showed clear-cut sarcomer formation. Desmin was first detected at nine weeks lining the cardiomyocyte plasma membrane, and after 17 weeks it showed the adult-like striated pattern of the protein. As expected, vimentin was already present in the mesenchymal cells from the first investigated time point, retaining a perivascular localization only towards higher ages. This is the first study that describes these vascular, muscular and mesenchymal factors on a large series of sequential human tissues, in an attempt to shed more light on the development of heart.