Congenital malformations in rats with the semilethal mutation fused pulmonary lobes

Syndactyly lethal: new mutation with multiple malformations occurring in Sprague Dawley rats

We previously found newborns exhibiting syndactyly of both fore- and hindlimbs in a litter from a pair of Sprague Dawley rats. Continuous breeding of the parental animals yielded pups with the same anomaly in following litters, suggesting that the syndactyly was genetic in origin. In the present study, as all the syndactylous pups died on postnatal day 0, we conducted genetic analyses using 30 phenotypically normal female progeny and the sire. The females were subjected to caesarean section on day 20 of gestation and the fetuses were examined for the phenotypes. The results of the mating experiments suggest that the mutant phenotype is caused by a single autosomal recessive gene at a homozygous condition. As homozygous mutants are lethal at the neonatal stage, the mutant gene was named syndactyly lethal, gene symbol syl. The mutant rats have multiple abnormalities, such as syndactyly, micrognathia, fused/absent/small lung lobes, absent kidney and ureter, small spleen, small uterus, fused phalanges, sternoschisis, absent/detached rib, and splitting/fused/absent/small thoracic vertebra, some of which must be the cause of death on postnatal day 0. This mutant is considered to be useful for investigating the mechanisms and/or pathogenesis of syndactyly, as well as the accompanying malformations.

Pathogenetic changes in the lung bud of mutant rats with heritable pulmonary lobation anomalies

The present study aimed at investigating pathogenesis of pulmonary lobation anomalies in fpl/fpl mutant rats. Day 12-15 embryos were first examined for pulmonary lobation. Lung serial sections were then made and examined for bronchial branching and distribution of extracellular matrices (ECMs). The lung buds of both fpl/fpl embryos and their phenotypically normal fpl/+ littermates were formed as bilateral protrusion of the foregut on gestation day 12. In fpl/+ embryos, three processes appeared on the right lung bud on day 13, and fissures were completely formed by day 14. In fpl/fpl embryos, the right lung bud had no clear process on gestation day 13, and fissures were not formed on day 14 and thereafter, with the exception of incomplete separation between the cranial and middle lobes. Histological observation revealed that the right main bronchial bud of fpl/+ embryos ramified all lobar bronchial buds by gestation day 13. ECMs, a borderline between endodermal bronchial buds and surrounding mesenchyme, disappeared at the distal end of each lobar bronchial bud. By contrast, in fpl/fpl embryos, the right main bronchial bud did not ramify the middle and intermediate lobar bronchial buds at its lateral and ventral portions, but swelled on gestation day 13. It was covered with ECMs at the lateral side but not at the ventral region, from which the middle and intermediate lobar bronchial buds arose on gestation day 14. These observations suggest that altered distribution of ECMs causes branching abnormalities of the lobar bronchial buds and subsequent lobation anomalies in fpl/fpl embryos.