Postcranial morphological features of homozygous tetraploid mouse embryos.

The postcranial morphological features of 22 homozygous tetraploid mouse embryos were studied. The latter were produced by electrofusion of blastomeres at the 2-cell stage in vitro, and were transferred to appropriate recipients that were autopsied on d 12-16 of gestation. Seven embryos were isolated on d 15 or d 16 of gestation and were developmentally equivalent to control diploid embryos of 13-14.5 d p.c. In each of these embryos, their sex could be determined from the histological analysis of their gonads. A further 15 embryos were isolated on d 12-14 of gestation and most were developmentally equivalent to controls of between 11-11.5 and 12-12.5 d p.c. The sex of these embryos could not be determined from the analysis of their gonads, as these were all at the 'indifferent' stage. Twelve of the 22 embryos had a normal postcranial axial morphology, while 10 had an abnormal postcranial axial morphology associated with an enormous omphalocele which contained most of the abdominal viscera and often, particularly in the more advanced specimens, the heart as well. In each of the 7 developmentally most advanced embryos studied, a major congenital abnormality involving at least one organ system was present, but none of these was believed to be life-threatening. The most interesting finding was that 3 of these embryos had abnormalities of the aortic arch arterial system; in 2 embryos the arch of the aorta was retro-oesophageal and retrotracheal, while a 3rd embryo had transposition of the great vessels associated with a right-sided descending aorta. In a 4th embryo, an aneurysmal dilatation of the posterior cardinal vein was present, and this was associated with the anomalous persistence of the left subcardinal/supracardinal venous system. These abnormalities represent a degree of mirror imaging of the normal vascular arrangement. Analysis of the gonads revealed that all of the embryos with vascular abnormalities in this group were male (XXYY), and no vascular abnormalities were present in the females (XXXX). The histological features of the viscera were normal. In 5 of the 15 developmentally less advanced embryos, the distal part of the bulbus cordis region of the heart was displaced medially, and consequently the outflow tract was located on the left part of the pericardial cavity rather than on the right where it is normally found. This may represent an early stage in the differentiation of the aortic arch arterial vascular anomalies indicated above. In 2 additional embryos, abnormally located (i.e. retro-oesophageal) innominate vessels were present.(ABSTRACT TRUNCATED AT 400 WORDS)