Antisense inhibition of engrailed genes in mouse embryos reveals roles for these genes in craniofacial and neural tube development.

The roles of engrailed-1 (En-1) and engrailed-2 (En-2) have been investigated during gastrulation and neurulation in mouse embryos. Using antisense oligonucleotides and murine whole embryo culture, early somite embryos were injected with antisense phosphorothioated oligonucleotides directed against En-1 or En-2 transcripts and then grown in vitro for 48 hr. Inhibition of En-1 by antisense targeting during this period resulted in embryos with craniofacial abnormalities, specifically loss of mid- and hindbrain tissue and hypoplasia in associated neural crest derived areas such as the face and first and second pharyngeal arches. In addition, En-1 appeared to be essential in early patterning of the neural tube. Embryos removed from culture as early as 8 hr following injection exhibited undulations in the presumptive spinal cord. Histological analysis of the affected neural tubes at 48 hr showed disrupted cytoarchitecture and in some cases, apparent dorsal-ventral duplication of the neural tube and underlying notochord. Using S100 beta as a notochord marker, embryos removed from culture at 8 or 12 hr following injection exhibited loss of S100 beta expression in the notochord region subjacent to affected neural tube segments, suggesting that S100 beta, or other notochordal genes, may be downstream components of the En-1 regulatory cascade. Furthermore, antisense inhibition of En-1 induced caudal dysgenesis, suggesting disruption in primitive streak function. Antisense targeting of En-2 expression of early somite stages produced few alterations in development, although approximately one third of the embryos exhibited a series of lateral folds in the spinal cord at the level of the forelimb-bud.(ABSTRACT TRUNCATED AT 250 WORDS)