Additional file 1.
Morphometric comparison of wild-type and Gpc1-/- forebrains. Freshly dissected adult brains were photographed from the dorsal surface. Tracings of the outline of the forebrain hemispheres were digitized and each curve converted to a series of points, in intervals of 0.03 radians, on a polar plot centered on its centroid. For each genotype, the curves from different brains were overlayed and rotated so that the medial edges of each tracing (which are relatively straight) were optimally aligned. (A) An example from the right hemisphere of nine mutant mice. An average curve was generated by calculating the average distance from the centroid for the family of curves at each angular position. (B) Curves representing one standard deviation above and below the average were similarly produced. (C) A single curve depicting the ratio of the average mutant and wild-type values at each angular position was then generated, and error bars around this curve were calculated from the square root of the sum of the squares of the relative errors (standard deviation/mean) for the two mutant and wild-type average curves; the comparison of nine mutant and four wild-type right hemispheres using this process is shown. The null hypothesis - that mutant and wild-type forebrains are identical in shape - implies that the ratio curve should be a perfect circle (that is, distance to the centroid for mutant and wild-type should differ by the same proportion at every angular position). As shown in (C), a circle (r = 0.937) fit within the error bars at every angular position, implying that mutant forebrains are approximately 6.3% smaller in linear dimension, with no significant difference in forebrain shape. Note that a 6.3% decrease in linear dimension is consistent with an 18% decrease in volume, comparable to the observed 15.5% decrease in total brain weight (Figure 2).
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Jen et al. Neural Development 2009 4:33 doi:10.1186/1749-8104-4-33