Fig. 4. Non-complementation between the rs mutation and a null allele of Lrp6. The Lrp6-null allele is designated as null. (A) Compound heterozygotes (rs/null), obtained from mating between rs/+ and null/+ at the newborn stage, exhibit a rudimentary tail (red arrowheads) and spina bifida aperta (yellow arrowheads) (4-6). (1-3) are either of +/+, rs/+, or null/+. (B-I) E14 fetuses of rs/rs (C,G), rs/null (D,H), or null/null (E,I) genotypes exhibit a clear gradient in the severity of the dysmorphology phenotypes, both externally (B-E) and internally (F-I). Note the presence of a variety of morphological defects in null/null (E), including micropthalmia (mo), micrognathia (mg), oligodactyly (od), hypomelia (hm), gastroschisis (gs), spina bifida aperta (sba) and axial truncation (at). In the skeletal samples (F-I), note the difference in the levels of axial truncation (arrowheads).