Cardiac samples from OTT1 null/null and OTT1 null/wt embryonic mice

The infant leukemia-associated gene, Ott1(Rbm15), has broad regulatory effects within the murine hematopoiesis. However, germline Ott1 deletion results in fetal demise prior to E10.5, indicating additional developmental requirements for Ott1. The spen gene family, to which Ott1 belongs, has a transcriptional activation/repression domain and RNA recognition motifs, and in Drosophila has a significant role in the development of the head and thorax. Early Ott1-deficient embryos show growth retardation and incomplete closure of the notochord. Further analysis demonstrated placental defects in the spongiotrophoblast and syncytiotrophoblast layers, resulting in an arrest of vascular branching morphogenesis. Rescue of the placental defect using a conditional allele with a trophoblast-sparing cre transgene allowed embryos to form a normal placenta and survive gestation. This result shows that the process of vascular branching morphogenesis in Ott1-deficient animals is regulated by the trophoblast compartment rather than the fetal vasculature. Mice surviving to term manifested hyposplenia and abnormal cardiac development. Analysis of global gene expression of Ott1-deficient embryonic hearts shows enrichment of hypoxia-related genes and significant alteration of several candidate genes critical for cardiac development. Thus, Ott1-dependent pathways in addition to being implicated in leukemogenesis, may also be important in the pathogenesis of placental insufficiency and cardiac malformations.

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Raffel GD, Chu GC, Jesneck JL, Cullen DE, Bronson RT, Bernard OA, Gilliland DG