Blood cells and cardiac myocytes go back a long way, having a common origin from the embryo's primitive streak as mesoderm appears. Although not sharing a common destination, with myocytes winding-up in the embryo's anterolateral quadrant and blood cells in the extraembryonic blood islands, their close relationship has been demonstrated in experiments wherein embryonic blood progenitor cells can be turned into cardiac myocytes (reviewed by Lough and Sugi, 2000). Evidence that the relationship between blood cells and cardiac myocytes persists in adults is provided by the ability of adult hematopoietic progenitor cells (HPCs) to differentiate into cardiac myocytes (Orlic et al., 2001) when present in a cardiac environment or “niche.” Because such de novo myocytes have been shown to improve damaged myocardium in experimental animals (reviewed by Anversa and Nadal-Ginard, 2002), these findings may have eventual clinical application. While considering such findings, it was intuitively appealing to Eisenberg et al. (2003) that HPC derivatives such as macrophages, which participate in wound healing, might also participate in myocardial healing. In the September 2003 issue of The Anatomical Record, Eisenberg and coworkers report results of their experiments indicating that adult bone marrow HPCs, under the influence of embryonic heart tissue or a defined growth factor cocktail derived therefrom, can differentiate into cardiac-like cells. (View the full article free on-line through Wiley InterScience: Eisenberg et al. (2003) at http://dx.doi.org/10.1002/ar.a.10106) The latter findings of Eisenberg et al. (2003), which indicate that HPCs can directly differentiate into nonblood cells in the absence of other cell types, challenge the universality of the emerging notion that HPCs indirectly differentiate as a consequence of fusing with existing cells in regenerating target tissue (Medvinsky and Smith, 2003). Moreover, evidence that transdifferentiation, another controversial mechanism (Wurmser and Gage, 2002), may participate in the regeneration process was obtained by additional experiments of Eisenberg and colleagues showing that terminally differentiated macrophages, when introduced to explanted cardiac tissue, could transdifferentiate into cardiac myocytes. The authors' rationale that macrophages may possess phenotypic plasticity due to their primitive position on the evolutionary ladder and that they were selected to participate in tissue regeneration as the mechanism of wound healing evolved, is an intriguing one that should provoke interesting follow-up experiments.

John W. Lough

The Anatomical Record

The Anatomical Record is an academic journal focused on the field of anatomy, covering both fundamental and applied research, aimed at promoting scientific communication and advancement in anatomy.

《解剖记录》是一本专注于解剖学领域的学术期刊，涵盖了相关的基础研究和应用研究，旨在促进解剖学的科学交流与发展。

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