ROSENMAN, B.A.*; LOVEJOY, C.O.; Kent State University; Kent State University: Morphological description of the pelvis of Fgf4 and Fgf8 conditional knockout mice

Transgenic animals are an important tool for elucidating morphogenesis and modularity, as well as current morphological issues such as the boundaries of units of selection and the putative role of mechanical stimuli in shaping the skeleton. Here we describe the pelvic phenotype in mice in which Fgf4 and Fgf8 have been conditionally inactivated in the early limb bud (�Fgf4/8 mutants�). In these animals, the hindlimbs lack all skeletal elements distal to the pelvic girdle. We analyzed 16 Fgf4/8 adult mutants and 14 wild-type littermates, controlling for sex and age. We used pQCT scans to create 3-D reconstructions of their pelvic girdles. While the sacrum, pubis, ischium, and ilium are present in all mutants, the acetabulae and anterior inferior iliac spines are absent. Most mutants possess variably dysmorphic ischia, and to a lesser degree, pubic corpora and rami, possibly as a consequence of decreased vascularity subsequent to reduced muscle formation in the truncated hindlimb. The iliac blades, however, were less dysmorphic. We performed a principal components analysis on four iliac measurements. PC1 and PC2 scores, accounting for 44% and 32% of the variance respectively, do not significantly differ between wild-type and mutant populations. We therefore conclude that the mutant ilia are essentially typical of the wild-type form, even in the absence of hindlimb forces. Similarly, a principal components analysis indicates that sacra do not differ between populations, except for increased sacralization of the S3 vertebra in Fgf4/8 mutants. These mutants suggest that genetic specification of the pelvic girdle differs from that of the rest of the limb. This fact must figure prominently in discussions of tetrapod hip evolution.