Lumbosacral plexus in Hoxa9 knockout mice with special reference to their nerve variations identified according to whether they were interphenotypic or intergenotypic differences.

The lumbosacral plexus in specific Hox gene mutant mice originating from C57bl/60, i.e., Hoxa9 +/+, +/- and -/- genotypes (10 specimens of each), were dissected minutely and detailed examinations were made of the eight nerves in the plexus and the lowest intercostal nerve. We identified three types of nerve variation in mice with Hox mutations: interphenotypic variations, intergenotypic variations and common variations regardless of the genotype axial phenotype. The interphenotypic variations involved a caudal shift of the nerve origin in mice with the Hoxa9 -/- axial phenotype. We divided these variations into three patterns according to whether or not nerve configurations in mice with the wild and/or Hoxa9 -/- axial phenotypes were consistent, as follows: 1) the iliohypogastric and pudendal nerve morphologies of either of the phenotypes were consistent; 2) the femoral, obturator and sciatic nerve morphologies of the wild axial phenotype were consistent, but those of the -/- phenotype showed several variations and 3) both phenotypes showed several variations of the ilioinguinal and genitofemoral nerves. The intergenotypic variations, were limited to two examples: the common trunk formation of the ilioinguinal and iliohypogastric nerves in mice with the +/- and -/- genotypes, regardless of their axial phenotypes, and the territory of the ilioinguinal nerve touched the lateral margin of the thigh in the wild genotype, but extended beyond the margin onto the posterior aspect in the -/- genotype. The common variations regardless of either axial phenotype or genotype, included the lateral cutaneous nerve of the thigh which showed a limited, common variation in both of the nerve origin, ramification pattern and territory among either the three genotypes or two axial phenotypes. We consider the interphenotypic variations to be consistent with previous experimental findings showing a discrepancy between the nerve origins and their cues for nerve pathfinding. However, this developmental sequence did not seem to apply to the intergenotypic or common variations.