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Relationship between genital ridge formation and settlement site of primordial germ cells in chick embryos
A Ukeshima1, M Kudo, T Fujimoto
1Kumamoto University College of Medical Science, Japan.
Insights
Primordial germ cells (PGCs) extravasate from blood vessels in chick embryos and migrate to the forming genital ridge. This study details their settlement sites and the developmental origins of the gonadal anlage.
Area of Science:
- Developmental biology
- Embryology
- Cell biology
Background:
- Primordial germ cells (PGCs) are crucial for reproduction and their developmental origins are a key area of study.
- Understanding PGC migration and settlement is vital for comprehending gonad development.
Purpose of the Study:
- To elucidate the detailed relationship between primordial germ cell settlement sites and the developing genital ridge in chick embryos.
- To identify the origin of the definitive gonadal anlage during early embryonic development.
Main Methods:
- Investigation of chick embryos (stages 15-18) using serial sections and light microscopy.
- Detailed observation of primordial germ cell extravasation and migration patterns.
Main Results:
- Primordial germ cells extravasate from vascular spaces in the splanchnopleure, posterior to the vitelline artery.
- Extravasation is localized to an area approximately 1.2 mm caudal to the vitelline artery.
- PGCs enter and are incorporated by the thickened coelomic epithelium, which subsequently migrates to form the genital ridge.
Conclusions:
- The thickened coelomic epithelium of the splanchnopleure, after incorporating PGCs, forms the superficial epithelium of the genital ridge.
- The thickened splanchnopleure epithelium at stage 16 is identified as the definitive gonadal anlage.
Abstract:
Chick embryos from stage 15 to stage 18, which is the most frequent extravasation period, were investigated by means of serial sections and light microscopy in order to learn the detailed relationship between the settlement sites of the primordial germ cells (PGCs) and the forming genital ridge. PGCs circulating in the vascular system came out of the small vessels in the splanchnopleure posterior to the vitelline artery. This PGC extravasation was limited to an area about 1.2 mm caudal to the vitelline artery. After the extravasation, the PGCs entered the neighboring thickened coelomic epithelium of the splanchnopleure. This thickened epithelium, which had incorporated the PGCs, changed the location toward the future gonadal site with the advance of development. At stage 16, the thickened portion of the epithelium was located in the splanchnopleure; then it moved toward the somatopleure via the coelomic angle; finally, at stage 18, this epithelium occupied the region between coelomic angle and the mesonephros which corresponded to the future genital ridge. This means that the thickened epithelium of the splanchnopleure which initially incorporated the PGCs becomes the superficial epithelium of the genital ridge in more advanced stages. The thickened portion of the epithelium of the splanchnopleure at stage 16 is thought to be the definitive gonadal anlage.