Functional dissection of XDppa2/4 structural domains in Xenopus development

The maintenance of pluripotency in mammalian embryonic stem cells depends upon the expression of regulatory genes like Oct3/4 and Sox2. While homologues of these genes are also characterized in non-mammalian vertebrates, like birds, amphibians and fish, existence and function of developmental pluripotency associated genes ( Dppa) in lower vertebrates have not yet been reported. Here we describe a Dppa2/4 -like gene, XDppa2/4 , in Xenopus.The protein contains a SAP domain and a conserved C-terminal region. Overexpression of XDppa2/4 , murine Dppa2 or Dppa4produces similar phenotypes (defects in blastopore closure), while injection of XDppa2/4 morpholino generates a loss of blastopore closure and neural fold formation. Embryos die up to tailbud stage. mDppa2 (but not mDppa4 ) rescues blastopore closure and neurulation defects caused by XDppaMO, but does not prevent subsequent death of embryos. Although XDppa2/4 exhibits a Dppa -like expression pattern and is indispensable for embryogenesis, analyses of various marker genes make its role as a pluripotency factor rather unlikely. Both the gain and loss of function effects until the end of neurulation are caused by the conserved C-terminal region but not by the SAP domain. The SAP domain is required for association of XDppa2/4 to chromatin and for embryonic survival at later stages of development suggesting epigenetic programming events.