Analysis of hematopoietic development during human embryonic ontogenesis.

We describe here diverse methods used to study the onset of hematopoiesis in the human embryo and fetus. In the first part of this chapter, the criteria for estimating developmental stages in human embryos are discussed. This section also presents in detail a refined method for embedding and freezing intact human embryonic tissues that are destined to be analyzed by histology and immunostaining. In the second section, several protocols for the microdissection of human embryos are described in detail, with special attention given to differences encountered between tissues at different ages of gestation. Because of the limited number of cells available at the early stages of human gestation, we have established a miniaturized cell amplification system permitting further development of intact organ rudiments dissected from a human embryo and cultured in toto. The last part of the chapter is devoted to the study of myeloid and lymphoid potentials using, respectively, a mouse bone marrow-derived stromal cell line and cultured mouse embryonic thymus rudiments.