The precardiac areas and formation of the tubular heart in the chick embryo

Stem cells and the formation of the myocardium in the vertebrate embryo

“…After allowing the embryos to develop to tubular heart stages, the fates of individual fluorescently tagged mesoderm cells were compiled, with regard to whether heart or nonheart tissue was subsequently labeled. Despite great differences in the methodology, the cardiac fate maps of Stalsberg and DeHaan (1969) and Redkar et al (2001) are almost identical. Within the HH stage 5 chick embryo, the medial border of the precardiac mesoderm is located ϳ0.3 mm lateral to the primitive groove.…”

“…At these stages, the embryo is a relatively simple structure consisting of the three primary germ layers. Cells fated to become heart tissue localize to paired regions of mesoderm within the anterior half of the embryo (Stalsberg and DeHaan, 1969;Keller, 1976;Stainier et al, 1993;Redkar et al, 2001). As development proceeds, the lateral mesoderm splits into distinct somatic and splanchnic layers (HH stages 6 -7 in the chick), with the precardiac cells sorting to the splanchnic mesoderm (DeHaan, 1963(DeHaan, , 1965Linask, 1992).…”

“…In reporting these findings, Rawles speculated that the actual precardiac fields were probably narrower than the map she defined for cardiac potency of embryonic tissue. This was borne out by the investigations of Stalsberg and DeHaan (1969), who radiolabeled small tissue fragments consisting of the mesoderm and endoderm layers (mesendoderm) from HH stage 5 embryos, which were subsequently transplanted into a second identically staged embryo, at the exact same position. Following their further development, these embryos were then sectioned and analyzed for the radioactive label.…”

“…Fate maps will provide the history of a cell's location within a developing embryo but cannot reveal a cell's potential and capabilities. Although the embryonic area corresponding to the precardiac mesoderm has been determined definitively (Stalsberg and DeHaan, 1969;Redkar et al, 2001), that fate map information does not tell us whether those stem cells are fully committed to become cardiomyocytes, and therefore no longer able to give rise to other lineages. In other words, fate mapping cannot determine whether the stem cells residing in the precardiac mesoderm are unipotential or multipotential.…”

Belief vs. scientific observation: The curious story of the precardiac mesoderm

“…This is the time during chick development when the primitive streak begins to recede and the notochord begins to form. At HH stage 5, the precardiac or heartforming regions (HFRs) comprise two mesodermal fields within the anterior half of the embryo, which are bilaterally distributed with respect to the embryonic axis (Rawles, 1943;Rosenquist and DeHaan, 1966;Stalsberg and DeHaan, 1969). This point in heart development either coincides with or is just prior to the initial expression of several cardiac-associated transcription factors, such as Nkx2.5, SRF, Tbx-5, GATA4-6, and MEF2C (Croissant et al, 1996;Evans, 1997;Black and Olson, 1998;Evans, 1999;Yamada et al, 2000).…”