Together, these studies suggest that expression of CD41 and cmyb marks nascent HSCs in the zebrafish AGM, and provide the means to further dissect HSC generation and function in the early vertebrate embryo. A similar wave of EMPs are produced in the posterior blood island of the zebrafish and, similarly, these EMPs are es- tablished before HSC emergence 40. Reproduced with permission from Forrester AM. Finally, we have analyzed the gene expression profiles of EMPs and AGM precursors to better understand the molecular cues that pattern the first definitive hematopoietic cells in the embryo. EGFP enhanced green fluorescent protein, ALPM anterior lateral paraxial mesoderm, PBI posterior blood island. Timelapse imaging and lineage tracing analyses demonstrate that AGM-derived precursors use a previously undescribed migration pathway along the pronephric tubules to initiate adult hematopoiesis in the developing kidney, the teleostean equivalent of mammalian bone marrow. around 18 hpf which populate the posterior blood island. Unlike EMPs, CD41(+) AGM cells colonize the thymus to generate rag2(+) T lymphocyte precursors. three-dimensional structure of zebrafish blood vessels where. referred to as the posterior blood island (Al-Adhami and Kunz. We have identified and prospectively isolated these cells by CD41 (itga2b) and cmyb expression. were analyzed in zebrafish, the importance of this gene in definitive hematopoiesis was. In this report, we demonstrate that a fourth wave of hematopoietic precursors arises slightly later in the zebrafish aorta/gonad/mesonephros (AGM) equivalent. We have previously shown that zebrafish EMPs arise in the posterior blood island independently from hematopoietic stem cells (HSCs). In both the zebrafish and the mouse, the first definitive precursors are committed erythromyeloid progenitors (EMPs) that lack lymphoid differentiation potential. Multipotent, or definitive, precursors are subsequently generated to produce the adult hematopoietic lineages. Monopotent, or primitive, precursors first give rise to embryonic macrophages or erythrocytes. Development of the vertebrate blood lineages is complex, with multiple waves of hematopoietic precursors arising in different embryonic locations.
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