<i>Sox17</i> Expression Patterns during Gastrulation and Early Neurulation in the Rabbit Suggest Two Sources of Endoderm Formation

Abstract

Most gastrointestinal tract and associated gland epithelia originate from the endoderm germ layer discovered by Pander in 1817. The recent surge in stem cell concepts revived interest in the findings of 30 years ago that the endoderm layer itself originates from the epiblast (which since Pander’s time had been held to be the forerunner of the ectoderm and mesoderm germ layers only). However, the question as to which parts of the mammalian gastrulation-stage embryonic disc generate endoderm cells is still unresolved. Therefore, the expression of the gene coding for the transcription factor Sox17, a key transcription factor involved in endoderm formation in mouse, chick, frog, and zebrafish, was analyzed in the rabbit, a model organism for mammalian gastrulation morphology, using whole-mount in situ hybridization and high-resolution histological analysis of embryos at gastrulation and early neurulation stages. Sox17 mRNA in the mesoderm and lower layer (hypoblast) compartments within and adjacent to Hensen’s node and the anterior segment of the primitive streak confirmed the validity of this approach, as this region had previously been shown to form endoderm in mouse and chick. However, Sox17 expression in central and posterior epiblast at pregastrulation stages together with a transient expression at the posterior extremity of the primitive streak suggest that endoderm (possibly hindgut) may be formed close to the emerging cloacal membrane, as well.

Sox17 and chordin are required for formation of Kupffer's vesicle and left‐right asymmetry determination in zebrafish

“…Sox17 is an endodermal factor known to be expressed in the DFC and KV in zebrafish and medaka (Kobayashi et al, 2006; Oteiza et al, 2008; Schneider et al, 2008), and in the area of the node in the mouse and chick (Chapman et al, 2007; Hassoun et al, 2009). Sox17 is downstream of cas , an endodermal gene also expressed in the DFC.…”

Paraxial <b><i>Nodal</i></b> Expression Reveals a Novel Conserved Structure of the Left-Right Organizer in Four Mammalian Species

“…Uteri of pigs, rabbits and mice were removed from euthanized animals as a whole and transferred into warm (37 ° C) phosphate-buffered saline (PBS) for blastocyst flushing (pig embryos, early-stage rabbit embryos) or dissection (olderstage rabbit embryos, mouse embryos) in PBS at room temperature as described before Hassoun et al, 2009). Cattle embryos were collected transcervically without the need for euthanasia as described by Richard et al [2014].…”

The hypoblast (visceral endoderm): an evo-devo perspective

“…However, there might also be a contribution from the posterior primitive streak for the cloacal region (Hassoun et al, 2010) and within the allantois (Mikedis and Downs, 2012). In addition, recent findings have raised the possibility that remnants of the AVE might remain in the final endodermal layer and contribute to the gut (Kwon et al, 2008) (Fig.…”