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The origin, migration and morphology of the primordial germ cells in the chick embryo
Insights
Chick primordial germ cells (PGCs) migrate via blood vessels or amoeboid movement to reach the developing gonads. These PGCs contain glycogen, yolk, lipids, and possess unique nuclear and cellular structures.
Area of Science:
- Developmental Biology
- Cell Biology
- Embryology
Background:
- Chick primordial germ cells (PGCs) originate from the germinal crescent endoderm.
- Early PGCs exhibit distinct morphological and migratory behaviors.
Purpose of the Study:
- To elucidate the migration pathways and cellular characteristics of chick primordial germ cells.
- To investigate the mechanisms of PGC colonization in developing gonads.
Main Methods:
- Observation of PGCs from early embryonic stages (4-10) through gonad development.
- Morphological analysis including light and electron microscopy.
- Histochemical staining for glycogen, yolk, and lipids.
Main Results:
- PGCs migrate through embryonic blood vessels from stage 10 onwards or via amoeboid movement in mesenchyme.
- Circulating PGCs emerge near gonads by day three, with amoeboid movement presumed for further migration.
- PGCs contain significant glycogen, yolk, lipids, and exhibit a characteristic fragmented nucleolus and well-developed organelles.
Conclusions:
- Chick PGCs utilize distinct migratory strategies, including vascular circulation and amoeboid movement.
- The presence of glycogen and specific ultrastructural features are key characteristics of developing PGCs.
- Understanding PGC migration is crucial for comprehending germline development and potential reproductive health insights.
Abstract:
Chick primordial germ cells (PGCs) which separated from the "germinal crescent" entoderm in the period from stages 4 to 8 circulated mostly through the developing blood vessels from stage 10 onward and finally migrated into the gonad. The PGCs making their appearance up to this stage were generally spherical in profile, about 14 mum in diameter. Some of the PGCs in contrast, did not enter the blood vessels but remained in the tissue (mesenchyme) of the embryo proper (tissue PGCs) and possessed pseudopodial processes, suggesting their migration by means of amoeboid movements. The circulating PGCs emerged from blood vessels in the vicinity of developing gonads by three days (gonadal PGCs). The principal mechanism responsible for the subsequent migration of gonadal PGCs is assumed to be amoeboid movements as in the case of tissue PGCs. Notable amounts of PAS-positive glycogen were demonstrated in the cytoplasm of PGCs in all stages obsreved. They also contained yolk and lipids intracytoplasmically, the former dissipating in relatively early stages of development. Electron microscopic observation revealed the electron-opaque, "fragmented nucleolus" in the large nucleus (8 mum in diameter), which represented another prominent feature of chick PGCs. PGCs contained a well-developed Golgi complex and endoplasmic reticulum.