Observation on in vitro development of black at hatch (Bh) lethal quail embryos with special reference to liver morphogenesis.

Homozygous and heterozygous embryos for Bh gene were cultured with mineral-rich (MR: using chicken egg shell) and mineral-free (MF: using Saran Wrap(R)) methods after 2.5 days of normal incubation. The homozygotes died at Stages 19 to 25 of ZACCHEI'S standardization (corresponding to 4.5 to 8 days of normal incubation) in MR culture and at Stages 17 to 25 (corresponding to 3.5 to 8 days of normal incubation) in MF culture. These lethal stages were almost the same as that of the homozygous embryos developed in ovo and characteristic syndromes of the lethal embryos were likewise degeneration of the liver tissue and whole body subcutaneous haemorrhage. The findings that some of the moribund ho-mozygous embryos contained air babbles in the capillaries of the chorioallantoic membrane suggested that weakening of capillaries occurred not only in the embryo body but also in the extraembryonic tissues. Local degeneration of liver tissue was found at the posterior tip of the liver in some embryos at 12 days of incubation. Incidence of this abnormality in the left lobe was higher in MF embryos (about 80%) than in MR embryos (about 50%) regardless of the genotypes. The incidence in the right lobe was higher in the Bh type embryos (about 20%) than in the wild type (about 7%). With regard to the embryos developed in ovo, the incidence in the left lobe was 36% and 8% in the Bh and wild type, respectively, and that in the right lobe was 0.2% in both genotypes. Thus, incidence of this abnormality was enhanced under the culture condition and in the Bh type embryos. Ultrastructural observation revealed increase in number of large lipid droplets in liver cells of cultured embryos. In the region showing local degeneration of liver tissue, the degenerated cells were clearly discernible from the adjacent healthy cells. Char-acteristics of the degenerated cells were as follows. Cytoplasm was thin and scattered. Mitochondria with dense matrix and numerous cristae and numerous lysosomes were fre-quently seen, whereas no glycogen granules were found. Ultrastructural feature of the degenerated cells was similar regardless of the genotypes of embryos or whether the samples were taken from the cultured embryos or those developed in ovo.ONO and WAKASUGI: Bh Lethal Quail Embryos in vitro 379