Insulin-Like Growth Factor-2 Regulation of Conceptus Composition: RESULTS(1)

In all experiments, the Igf2 null allele was transmitted by a heterozygous father, giving the genotypes Igf2 +m/-p (subsequently called Igf2ko) and Igf2 +m/+p (subsequently called ‘‘normal’’). ventolin 100 mcg

Nonmanipulated Conceptuses

To provide a baseline for the recombination experiments, observations were made on nonmanipulated conceptuses from 129J/Sv matings. The wet weight, dry weight, and DNA content of conceptuses were compared at E16.5 (Table 1).

To reduce the variation between the size of conceptuses in different litters, litters were selected in which the wet weight of the normal conceptuses did not exceed 1 g in both the wet and dry weights and the DNA content series. For the wet and dry weight series, the Igf2 ko total con-ceptus weights were significantly decreased compared to the normal ones (35% wet weight, 37% dry weight, mean 3.78 viable conceptuses per horn). There was no evidence that the Igf2 ko conceptuses were unusually dry. In the DNA content litters, the Igf2 ko samples had 31% lower total conceptus weights and 32% lower total placenta + fetus wet weights (mean 3.67 viable conceptuses per horn). The estimated fluid volume of the exocelomic and amniotic cavities was reduced by 25%. However, tissue composition was altered because the DNA content was only reduced by 15%. These results showed that the Igf2 +m/-p genotype severely reduced wet and dry weight growth but that it had a minor effect on DNA content.

TABLE 1. Wet weight, dry weight, fluid, and DNA contents of Igf2 ko and normal E16.5 conceptuses, comparing Igf2 ko conceptuses with normals in the same litters (mean ± SD).

Series n Wet weight, total conceptus (g) n Dry weight, total conceptus* (g) n Wet weight, fetus + total placenta* (g) n Exocoelomic + amniotic volume* (ml) n DNA content, fetus + total placenta* (M$
Wet & dry weight
lgf2+m/+p 33 0.901 ± 0.139 33 0.100 ± 0.024 nd nd nd
lgf2+m‘-p 29 0.589 ± 0.078a 29 0.063 ± 0.013a nd nd nd
Percent normal (Cl) 65% (59-72%) 63% (53-75%)
Wet weight & DNA content
lgf2+m/+p 24 0.799 ± 0.071 nd 24 0.564 ± 0.066 24 0.202 ± 0.014 24 2294 ± 427
lgf2+m‘-p 39 0.554 ± 0.056a nd 42 0.383 ± 0.051a 39 0.152 ± 0.013a 42 1952 ± 605b
Percent normal (Cl) 69% (65-74%) 68% (62-73%) 75% (72-79%) 85% (69-96%)

* nd, Not determined. a p < 0.000; b p < 0.01.

TABLE 2. Comparison of successful development to E16.5 after recombination of the blastocyst.

Proportion No. transferred to Number (%) Proportion with Igf2 ko
of pregnant pregnant of viable genotype
Series recipients recipients conceptuses in part
ICM 9/9 49 40 (82%) 20/40
Trophectoderm 10/12 58 38 (66%) 27/38
This entry was posted in Growth Factor and tagged Genotypes, Growth Factor, Inner Cell Mass, Trophectoderm.