List of abbreviations
CDH, congenital diaphragmatic hernia; PPF, pleuroperitoneal fold(s)
Footnote 1: In the film Who Framed Roger Rabbit (copyright The Walt Disney Company and Amblin Pictures, 1988), animated characters are combined with real actors. Here we use the phrase "Roger Rabbit" to denote the merging of real data components with simulated cells in our computer model.
Footnote 2: Historically, both the mouse and rat have been used to study diaphragm development and nitrofen-induced CDH. Comparable embryonic stages are as follows: mouse (rat) – 11.5 (13), 12 (13.5), 12.5 (14), 13 (14.5), 13.5 (15), 14 (15.5).
Footnote 3: Nudge++™ is used under license from Olana Technologies, Inc., 5424 Arlington Avenue, H51, Bronx, New York, United States 10471.
Footnote 4: There are currently no data on cell size or density in the developing diaphragm. Also, data on cell cycle times are lacking. In these simulations, cell volume is set at 525 μm2 yielding a radius of about 5 μm. Alteration in absolute cell size should not affect the key features of the simulations since changes in cell size can be offset by changes in cell number and mitotic rate. Likewise, we have chosen cell cycle times as sufficient to fill the projected area of the developing diaphragm in the allotted time. In general, cycle time is designated as equal throughout the tissue but increases gradually over simulated embryonic time, i.e. mitotic rate slows as the embryo ages. Further details for each simulation are provided in the Results section and the appropriate figure legends.
Footnote 5: Alternatives include: (i) the PPF (cell mass) remains fixed to the body wall and moves laterally as the body wall expands, (ii) the PPF remains fixed to the dorsal mesentery, and (iii) the PPF remains fixed in free (absolute) space. These alternatives were examined for completeness but do not change the key simulation results as presented here (data not shown).
Footnote 6: Whereas there need not be a strict correlation between cells becoming post-mitotic and cells undergoing differentiation, this is a convenient shorthand in the present case. The actual topography of mitotic activity in the developing diaphragm is not known, nor is it known to what extent the degree of differentiation of these myoblasts coincides with mitotic activity or perhaps cell fusion.
Footnote 7: Although some large defects seem to have no posterior rim, many have a very small rim tucked into the retroperitoneum. Indeed, one component of the surgical repair of CDH is "unfurling" of this small, occult rim of diaphragm.
Footnote 8: It is important to note that medial is actually slightly off the true midline (where reside the esophagus, aorta, inferior vena cava and spine). This usage also is consistent with Morgagni-type anterior defects that are generally described as anteromedial although when unilateral they present slightly off the actual midline.
We are grateful to Ms. Adrienne Grzenda for technical assistance and to Drs. Marc Arkovitz and Charles Stolar for discussion and review of the manuscript. This work was supported in part by a Start-Up Grant from the Department of Surgery, College of Physicians and Surgeons, Columbia University.