Development of cytoskeletal connections between cells of preimplantation mouse embryos

Area of Science:

• Developmental Biology
• Cell Biology
• Embryology

Background:

• Mouse cleaving embryos exhibit microvilli at cell contact sites.
• These microvilli connect the cortical cytoskeletons of adjacent blastomeres.

Purpose of the Study:

• To investigate the nature and formation of microvilli-associated cytoskeletal connections during early mouse embryonic development.
• To determine the molecular components and regulatory factors involved in establishing these connections.

Main Methods:

• Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to visualize microvilli and cytoskeletal structures.
• Biochemical assays including heavy meromyosin (HMM) decoration and DNase I digestion identified actin microfilaments.
• Pharmacological treatments (cytochalasin D, colchicine) and altered media conditions (low Ca2+/Mg2+, EGTA, α-lactalbumin) were employed to assess factors influencing connection formation.

Main Results:

• Long microvilli bridging blastomeres were observed, corresponding to cytoskeletal strings in detergent-extracted morulae.
• These connections, appearing 4 hours post-compaction, contain actin microfilament bundles.
• Connection establishment is independent of immediate protein synthesis but is inhibited by cytochalasin D and delayed by colchicine.

Conclusions:

• Cytoskeletal connections mediated by microvilli are established early in mouse embryogenesis, coinciding with compaction.
• Actin microfilaments form the structural basis of these connections, which are sensitive to specific cytoskeletal inhibitors.
• These findings shed light on the structural dynamics underlying compaction and blastulation in mammalian embryos.