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Origin of primordial germ cells in the prestreak chick embryo
L Karagenç1, Y Cinnamon, M Ginsburg
1Department of Poultry Science, North Carolina State University, Raleigh, NC 27695, USA.
Insights
The avian germline segregates gradually, involving SSEA-1/EMA-1 positive cells moving from the area pellucida to the hypoblast. This epigenetic process is crucial for primordial germ cell development in early avian embryos.
Area of Science:
- Developmental Biology
- Cell Biology
- Embryology
Background:
- The early development of the avian germline is critical for reproduction.
- Understanding the precise timing and location of primordial germ cell (PGC) segregation is essential.
Purpose of the Study:
- To investigate the temporal and spatial patterns of avian germline segregation.
- To identify the cellular origins and molecular markers associated with PGC development.
Main Methods:
- Culture of whole avian embryos and fragments at early developmental stages (VII-IX).
- Immunohistological analysis using stage-specific embryonic antigen-1 (SSEA-1) and EMA-1 antibodies.
- Culture of dispersed blastoderm cells with and without feeder layers.
Main Results:
- PGCs were detected in whole embryo cultures and central fragments at stages VII-IX.
- Dispersed blastoderms from stage X-XIV embryos yielded PGCs, with significantly more found when cultured on feeder layers.
- SSEA-1/EMA-1 epitopes appeared at stage X on epiblast and hypoblast cells, with SSEA-1-positive hypoblast cells generating PGCs.
Conclusions:
- Avian germline segregation is a gradual, epigenetic process.
- Cellular translocation from the area pellucida to the hypoblast, marked by SSEA-1/EMA-1 expression, is key to PGC development.
Abstract:
The temporal and spatial pattern of segregation of the avian germline from the formation of the area pellucida to the beginning of primitive streak formation (stages VII-XIV, EG&K) was investigated using the culture of whole embryos and central and peripheral embryo fragments on vitelline membranes at stages VII-IX, immunohistological analysis of whole mount embryos and sections with monoclonal antibodies MC-480 against stage-specific embryonic antigen-1 (SSEA-1) and EMA-1, and with the culture of dispersed blastoderms at stages IX-XIV with and without on STO feeder layer. Whole embryos at intrauterine stages developed up to the formation of the primitive streak despite the absence of area pellucida expansion. Primordial germ cells (PGCs) appeared in the cultures of whole embryos and only in central fragments containing a partially formed area pellucida at stages VII-IX. When individual stage IX-XIV embryos were dispersed and cultured without a feeder layer, 25-45 PGCs/embryo were detected only with stage X-XIV, but not with stage IX blastoderms. However, the culture of dispersed cells from the area pellucida of stages IX-XIII on STO feeder layers yielded about 150 PGCs/embryo. The carbohydrate epitopes recognized by anti-SSEA-1 and EMA-1 first appeared at stage X on cells in association with polyingressing cells on the ventral surface of the epiblast and later on the dorsal surface of the hypoblast. The SSEA-1-positive hypoblast cells gave rise to chicken PGCs when cultured on a feeder layer of quail blastodermal cells. From these observations, we propose that the segregation and development of avian germline is a gradual, epigenetic process associated with the translocation of SSEA-1/EMA-1-positive cells from the ventral surface of the area pellucida at stage X to the dorsal side of the hypoblast at stages XI-XIV.