Heterochronic limb patterning in marsupials reveals flexibility in the processes underlying lateral plate mesoderm morphogenesis

Abstract

Marsupial embryos develop under intense functional constraints: neonates are born after a short gestation but must immediately crawl to the teat using precociously developed forelimbs. To meet this demand, marsupials have evolved extreme acceleration of limb morphogenesis, yet the cellular and molecular mechanisms underlying this shift remain unresolved. Using two distantly related marsupials, the fat-tailed dunnart (Sminthopsiscrassicaudata) and the gray short-tailed opossum (Monodelphis domestica), we show that this acceleration extends upstream to the earliest stages of lateral plate mesoderm (LPM) formation. The forelimb field is specified in relative isolation from other axial structure..