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Expression of cell death regulatory genes and limited apoptosis induction in avian blastodermal cells
D E Muscarella1, M K Rachlinski, S E Bloom
1Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA.
Abstract:
Apoptosis is a well-established cellular mechanism for selective cell deletion during development. However, little is known about the expression of an apoptotic pathway and its role in determining the relative sensitivity of the early, pre-gastrula, avian embryo to stress-induced cell death. We examined the sensitivity of avian blastodermal cells to engage in apoptosis upon exposure to etoposide, a topoisomerase II-inhibitor that rapidly and efficiently induces apoptosis in many cell types. We found that while the blastodermal cells are capable of engaging in apoptosis, they are highly resistant to such induction with respect to both concentration of drug required and length of exposure, even when compared to a tumor cell line with a known multi-drug resistant phenotype. Additionally, we assessed the expression of several candidate regulatory genes in blastodiscs from infertile eggs (i.e., maternal RNA transcripts), blastodermal cells immediately following oviposition, and various stages of early development up to gastrulation. This analysis revealed that several genes whose products have anti-apoptotic activity, including bcl-2, bcl-xL, hsp70, grp78 and the glutathione S-transferases, are expressed as early as the stage 1 embryo in the newly oviposited egg. These transcripts are also found in the infertile blastodisc, suggesting a role for maternally derived transcripts in the protection of the oocyte and zygote. Significantly, constitutive levels of hsp70 mRNA exceeded those of the other anti-apoptotic genes in the blastodermal cells. These results contribute to an emerging picture of stress resistance at the earliest stages of avian embryo development which involves multiple anti-apoptotic genes that act at different regulatory points in the apoptotic cascade.
Insights
Early avian embryos exhibit remarkable resistance to apoptosis, even when exposed to toxic drugs. This stress resistance is mediated by multiple anti-apoptotic genes, including hsp70, expressed from the earliest developmental stages.
Area of Science:
- Developmental Biology
- Cellular Biology
- Apoptosis Research
Background:
- Apoptosis is crucial for development, but its role in early avian embryos is unclear.
- Understanding stress-induced cell death sensitivity in pre-gastrula embryos is essential.
Purpose of the Study:
- To investigate the apoptotic pathway sensitivity of early avian embryos.
- To identify anti-apoptotic gene expression in early avian development.
Main Methods:
- Exposure of avian blastodermal cells to etoposide, a topoisomerase II-inhibitor.
- Analysis of anti-apoptotic gene expression (bcl-2, bcl-xL, hsp70, grp78, glutathione S-transferases) via RT-PCR.
- Assessment of gene expression in infertile blastodiscs, newly oviposited eggs, and developing embryos up to gastrulation.
Main Results:
- Avian blastodermal cells are highly resistant to etoposide-induced apoptosis compared to resistant tumor cell lines.
- Multiple anti-apoptotic genes, including bcl-2, bcl-xL, hsp70, grp78, and glutathione S-transferases, are expressed early in development.
- Maternally derived transcripts contribute to early embryo protection, with hsp70 showing high constitutive expression.
Conclusions:
- Early avian embryos possess inherent resistance to apoptosis due to the presence of multiple anti-apoptotic genes.
- Maternal factors play a significant role in protecting the oocyte and zygote.
- Hsp70 is a key contributor to the stress resistance observed in early avian development.