Type II keratins precede type I keratins during early embryonic development

Area of Science:

• Developmental Biology
• Cell Biology
• Molecular Biology

Background:

• The mammalian keratin (K) gene family is more complex than previously understood.
• Understanding keratin spatio-temporal expression is crucial for elucidating their function during early embryonic development.

Purpose of the Study:

• To investigate the expression patterns of selected mouse keratins from pre-implantation to mid-gestation.
• To characterize the regulation of keratin filament formation during early embryogenesis.

Main Methods:

• Reverse transcription-polymerase chain reaction (RT-PCR) to detect keratin transcripts.
• Immunofluorescence microscopy to visualize keratin protein localization and filament formation in embryonic tissues.

Main Results:

• Keratin transcripts (K5, K6, K7, K8, K14, K15, K18, K19) were absent at E0.5.
• Post-transcriptional regulation prevented keratin filament formation in 8- to 16-cell stage embryos; K7 and K8 proteins formed aggregates.
• Keratin filaments formed after K18 protein accumulation at E3.5; K5 and K14 expression was delayed.
• In K5-/- embryos, K14 formed filaments with K8 until E12.5, and K14 later aggregated without causing cytolysis.

Conclusions:

• Keratin filament formation during early embryogenesis is regulated by post-transcriptional mechanisms.
• The formation of the initial embryonic cytoskeleton from soluble keratins involves unknown regulatory processes.
• The role of premature type II keratin expression in signaling pathways requires further investigation.