Morphological features of mutant rat, IS-Tlk/Kyo, fetuses with caudal vertebral anomalies

ABSTRACT IS‐Tlk/Kyo, a rat mutant strain derived from IS/Kyo strain, exhibits a kinked and/or short tail, in addition to a congenital anomaly of the lumbar vertebrae that is a hallmark of IS/Kyo rats. Homozygotes (Tlk/Tlk) of Tlk dominant gene are known to die during embryonic development. The present report deals with the morphological features of heterozygous IS‐Tlk/Kyo rat fetuses in comparison with those of IS/Kyo rat fetuses. One of the morphological features was a high incidence of tail vertebral anomalies in IS‐Tlk rats (81.6% versus 0% in IS/Kyo rats). Significantly low values in number of live fetuses and ossified 5th sternebra and sacral and caudal vertebrae were observed in IS‐Tlk/Kyo rats compared with those in IS/Kyo rats as well as a low incidence of fetuses with ventral septal defects in IS‐Tlk/Kyo (0% versus 54.4% in IS rats). These results suggest that the Tlk gene may be involved in the formation of the vertebral centra and the ventral septum when it expresses on the genetic background of the IS rat.