Mouse 89 kD heat shock protein. Two polypeptides with distinct developmental regulation

Area of Science:

• Molecular Biology
• Developmental Biology
• Cellular Stress Response

Background:

• Unstressed early mouse embryos synthesize 70 and 89 kD heat shock proteins (HSPs) at high rates.
• It was previously unclear if this spontaneous synthesis involved heat shock-inducible or non-inducible (cognate) genes.

Purpose of the Study:

• To investigate the nature of spontaneous heat shock protein synthesis in early mouse embryos.
• To determine if the 89 kD heat shock protein (HSP89) is heat shock-inducible or cognate.
• To examine the developmental regulation of HSP89 expression.

Main Methods:

• High-resolution polyacrylamide gel electrophoresis (PAGE) to separate HSP89 components.
• Limited proteolysis to analyze peptide patterns.
• Analysis of distinct messenger RNA (mRNA) synthesis.
• In vitro differentiation of embryonal carcinoma (EC) cells.

Main Results:

• The 89 kD mouse HSP (HSP89) separates into two distinct proteins, HSP89f and HSP89s, with related peptide patterns.
• HSP89f is synthesized at high rates by unstressed cells and is stress-insensitive.
• HSP89s synthesis is heat-inducible in fibroblasts but is a major protein in unstressed preimplantation embryos and EC cells.
• Spontaneous synthesis of HSP89s decreases after in vitro differentiation of EC cells.

Conclusions:

• Spontaneous synthesis of HSP89f occurs in unstressed early mouse embryos and EC cells.
• HSP89s is an inducible mammalian heat shock protein whose spontaneous expression is developmentally regulated.
• The findings suggest a role for inducible HSPs in early mammalian development beyond stress response.