Origin and differentiation of the yolk sac and extraembryonic mesoderm in presomite human and rhesus monkey embryos

Abstract

Reexamination of presomite human and rhesus monkey embryos in the Carnegie Collection provides no evidence to corroborate the hypothesis that the trophoblast is the source of all extraembryonic tissues in these embryos. Instead, the present study indicates that the developmental pattern of the yolk sac and extraembryonic mesoderm is homologous to that in other eutharian mammals. The primary yolk sac of 10- to 11-day human blastocysts is partially filled with a meshwork of extraembryonic endoderm, whereas such a meshwork is absent in the rhesus monkey. It is suggested that this endodermal meshwork develops as the result of interstitial implantation in the human embryo. A small secondary yolk sac develops in 12- to 13-day human and macaque embryos as the result of pinching off of a portion of the larger primary yolk sac. Development of a secondary yolk sac in higher primates appears to be related causally to differential rates of expansion of the blastocyst and primary yolk sac within the simplex uterus. The caudal margin of the primitive streak develops precociously in 12- to 14-day human and macaque embryos, and this appears to be the source of all the extraembryonic mesoderm of the chorion, chorionic villi, and body stalk. It is suggested that the peripheral spread of extraembryonic mesoderm plays in inductive role in the development of chorionic villi, similar to other types of epithelial-mesenchymal inductive interactions. In contrast to previous hypotheses, the human and macaque trophoblasts appear to give rise only to additional trophoblast.

On the origin of amniotic stem cells: of mice and men

“…C mal component. Extraembryonic amniotic mesoderm was considered an epiblast-derived tissue in human and rhesus monkey (Hill, 1932;Luckett, 1978), which is in accordance to the situation in other eutherian species. Luckett's study (1978) reports the appearance of a thickening at the caudal margin of the embryonic disc around 12 dpf.…”

“…2C, model A). In contrast, a more recent study suggests that amniotic mesoderm has only an epiblast origin (Robinson et al, 2002), which is consistent with primitive streak-derived amniotic mesoderm (Hill, 1932;Luckett, 1978). Robinson and co-workers investigated the frequency of trisomic cells in amniotic epithelium and mesenchyme from human fetuses with placental mosaicism for trisomy.…”

Yolk-sac hematopoiesis

“…The first yolk-sac blood islands are evident morphologically in the secondary yolk sac beginning at approximately day 18 of gestation [91,92]. The developmental origin of blood cells and endothelial cells that make up the blood islands is also thought to be the endoderm of the yolk sac.…”

RNA-seq reveals conservation of function among the yolk sacs of human, mouse, and chicken

“…The yolk sac produces predominantly nucleated erythrocytes, which synthesize embryonic hemoglobin (HBZ). There is morphological evidence of the first blood islands in the secondary yolk sac at about day 18 of gestation (49). Yolk sac-derived primitive erythrocytes have been detected in the cardiac cavity as early as the three-somite stage (21 d), indicative of an established functional network between the yolk sac and embryo (50).…”