Morphological Features of Adult Rats of IS/Kyo and IS-Tlk/Kyo Strains with Lumbar and Caudal Vertebral Anomalies

IS-Tlk/Kyo, a mutant derived from IS/Kyo strain, exhibits a kinked and/or short tail, in addition to the congenital lumbar vertebral anomaly. Homozygotes of Tlk dominant gene are known to die during embryonic development. We previously reported the morphological features of the skeleton in IS/Kyo and IS-Tlk/Kyo fetuses and of the heart in IS/Kyo fetuses [19]. This study was conducted to clarify the morphological features of the skeleton in both adult rats and of the heart in adult IS/Kyo rats. Ventricular septal defect (VSD) was observed in 3 out of 10 IS/Kyo rats. Neither splitting of lumbar vertebra and supernumerary rib (in both strains) nor fused or absent caudal cartilage (in IS-Tlk/Kyo strain) was detected in adult rats. Fusion of lumbar vertebrae was observed in almost all specimens together with lumbarization of sacral vertebrae in a few specimens in both adult rats as well as fusion of sacral and caudal vertebrae only in adult IS-Tlk/Kyo rats. In addition, a severe reduction in the ossified sacral and caudal vertebrae was noted in adult IS-Tlk/Kyo rats (mean number: 20.6) and IS/Kyo rats (31.8), and the difference was similar to that in the length of sacral and caudal vertebrae. These results suggest that the Tlk gene may be involved in both the congenital and acquired abnormal formation of the lower vertebral centra as well as the persistent occurrence of VSD by the background gene in IS/Kyo strain.