Hypoblast

Hypoblast
Human Embryo Day9.png
Human Embryo in day 9. Hypoblast (brown) is beneath the epiblast (pink)
Details
Days8
Precursorinner cell mass
Gives rise toendoderm
Identifiers
Latinhypoblastus
TEE6.0.1.1.3.0.4
Anatomical terminology

The hypoblast is a cell mass that forms from the inner cell mass during early embryonic development. It develops into the endoderm and helps to orient the embryo and create bilateral symmetry.

Structure

The hypoblast lies beneath the epiblast and consists of small cuboidal cells.[1] The hypoblast gives rise to the yolk sac, which in turn gives rise to the chorion. The epiblast gives rise to the embryo itself, through the three germ layers, the endoderm, mesoderm and ectoderm.

The absence of hypoblast results in multiple primitive streaks in chicken embryos.[2] In birds, the formation of the primitive streak is induced by the Koller's sickle.[3]

Function

Although the hypoblast does not contribute to the embryo, it influences the orientation of the embryo. The hypoblast also inhibits primitive streak formation by depositing extracellular matrix components. [4] The primitive endoderm derived yolk sac has a major function in guaranteeing the proper organogenesis of the fetus and efficient exchange of nutrients, gases and wastes.

History

In mammals, the existence of primitive endoderm had been observed as early as the end of the 19th century as first recognized by Duval and Sobotta.[5][6] However, it took a long time before people realized that the primitive endoderm will be replaced by definitive endoderm which will further develop into the gut tube. The first convincing experiment was conducted by Bellairs in chick embryo with the careful observation under electron and light microscopy. In his experiment, Bellairs demonstrated that there is a transitory endoderm cell layer in the chick embryo at its ventral surface before the formation of primitive streak.[7] This layer of cell was replaced by definitive endoderm migration from the primitive streak through ingression and de-epithelialization.[8][9][10][11] Later on, more insights on primitive endoderm and definitive endoderm origin and formation have been shown in rat and mouse, rhesus monkey and baboon.[12][13][14][15][16]

References

  1. ^ Moore, K. L., and Persaud, T. V. N. (2003). The Developing Human: Clinically Oriented Embryology. 7th Ed. Philadelphia: Elsevier. ISBN 0-7216-9412-8.
  2. ^ Perea-Gomez A, Vella FD, Shawlot W, Oulad-Abdelghani M, Chazaud C, Meno C, Pfister V, Chen L, Robertson E, Hamada H, Behringer RR, Ang SL (2002). "Nodal antagonists in the anterior visceral endoderm prevent the formation of multiple primitive streaks". Dev Cell. 3 (5): 745–56. doi:10.1016/S1534-5807(02)00321-0. PMID 12431380.
  3. ^ Gilbert SF. Developmental Biology. 10th edition. Sunderland (MA): Sinauer Associates; 2014. Early Development in Birds. Print
  4. ^ Egea J., Erlacher C., Montanez E., Burtscher I., Yamagishi S., Hess M., Hampel F., Sanchez R., Rodriguez-Manzaneque M. T., Bosl M. R., et al. (2008). Genetic ablation of FLRT3 reveals a novel morphogenetic function for the anterior visceral endoderm in suppressing mesoderm differentiation.Genes Dev. 22, 3349–3362.
  5. ^ Duval M. (1891). The rodent placenta. Third part. The placenta of the mouse and of the rat. J. Anat. Physiol. Normales et Pathol. de l’Homme et des Animaux 27, 24-73; 344-395; 515-612.
  6. ^ Sobotta J. (1911). Die Entwicklung des Eies der Maus vom ersten Auftreten des Mesoderms an bis zur Ausbildung der Embryonalanlage und dem Auftreten der Allantois. I. Teil: Die Keimblase. Archiv. fur mikroskopische Anatomie 78, 271–352.
  7. ^ UNSW Embryology- Glossary H Archived 2007-08-18 at the Wayback Machine
  8. ^ Bellairs R. (1953a). Studies on the development of the foregut in the chick blastoderm. 1. The presumptive foregut area. J. Embryol. Exp. Morph. 1, 115–124.
  9. ^ Bellairs R. (1953b). Studies on the development of the foregut in the chick blastoderm. 2. The morphogenetic movements. J. Embryol. Exp. Morph. 1, 369–385.
  10. ^ Bellairs R. (1964). Biological aspects of the yolk of the hen’s egg. Adv. Morphog. 4, 217–272.
  11. ^ Bellairs R. (1986). The primitive streak. Anat. Embryol.
  12. ^ Enders A. C., Given R. L., Schlafke S. (1978). Differentiation and migration of endoderm in the rat and mouse at implantation. Anat. Rec. 190, 65–77.
  13. ^ Enders A. C., Schlafke S., Hendrickx A. G. (1986). Differentiation of the embryonic disc, amnion, and yolk sac in the rhesus monkey. Am. J. Anat. 177, 161–185.
  14. ^ Enders A. C., Lantz K. C., Schlafke S. (1990). Differentiation of the inner cell mass of the baboon blastocyst. Anat. Rec. 226, 237–248.
  15. ^ Gardner R. L. (1982). Investigation of cell lineage and differentiation in the extraembryonic endoderm of the mouse embryo. J. Embryol. Exp. Morphol. 68, 175–198.
  16. ^ Gardner R. L. (1984). An in situ cell marker for clonal analysis of development of the extraembryonic endoderm in the mouse. J. Embryol. Exp. Morphol. 80, 251–288.

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