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Electron microscopic studies on primary mesenchyme cell ingression and gastrulation in relation to vegetal pole cell
1Misaki Marine Biological Station, University of Tokyo, Japan.
Abstract:
Early morphogenetic events of primary mesenchyme cell (PMC) ingression and gastrulation were examined by scanning and transmission electron microscopy, with special attention directed to changes in the shape of vegetal pole cells, the length of their microvilli, and interactions between microvilli and the hyaline layer (HL). Eight cells (vegetal pole cells) with elongated microvilli remained in the vegetal pole region while surrounding cells ingressed into the blastocoel to form the primary mesenchyme. These vegetal pole cells indented with the surrounding cells at the stage of gastrulation. The outer surface area with elongated microvilli of vegetal pole cells expanded at the stage of PMC ingression, but was considerably reduced at gastrulation. Microvilli on vegetal pole cells continued to adhere to the HL up to the stage of PMC ingression, but ceased to do so at the time of gastrulation. Thus, the area with separated HL, which is restricted to the region of the PMC released at the stage of PMC ingression, spreads almost entirely throughout the area of the indenting vegetal plate at gastrulation. The apical lamina, apparently consisting of fibrous material intertwinning the stalks of the microvilli, filled the space between the HL and ectodermal cells. The cells surrounding those of the vegetal pole and indenting with those at the stage of gastrulation appeared to behave in the same way as ingressing PMCs in both cell-shape and loss of adhesion of microvilli to HL. The role of vegetal pole cells in early morphogenetic events is discussed.
Insights
Early sea urchin development involves primary mesenchyme cell (PMC) ingression and gastrulation. Vegetal pole cells change shape and microvilli interaction with the hyaline layer (HL) during these crucial early morphogenetic events.
Area of Science:
- Developmental Biology
- Cell Biology
- Marine Biology
Background:
- Early embryonic development relies on precise cell movements and interactions.
- Primary mesenchyme cell (PMC) ingression is a key event in gastrulation.
- The hyaline layer (HL) plays a role in early embryonic cell adhesion.
Purpose of the Study:
- To investigate the ultrastructural changes of vegetal pole cells during early sea urchin morphogenesis.
- To analyze the dynamic interactions between vegetal pole cell microvilli and the hyaline layer (HL).
- To understand the role of vegetal pole cells in primary mesenchyme cell (PMC) ingression and gastrulation.
Main Methods:
- Scanning electron microscopy (SEM) for surface morphology.
- Transmission electron microscopy (TEM) for ultrastructural details.
- Observation of cell shape, microvilli length, and hyaline layer (HL) interactions.
Main Results:
- Vegetal pole cells exhibit elongated microvilli and adhere to the hyaline layer (HL) during PMC ingression.
- Microvilli adhesion to the HL ceases at gastrulation, coinciding with vegetal pole cell indentation.
- The apical lamina forms between the HL and ectodermal cells, potentially influencing cell behavior.
Conclusions:
- Vegetal pole cells undergo significant shape and surface changes during gastrulation.
- Altered microvilli-HL interactions are critical for vegetal pole cell behavior and gastrulation.
- The behavior of surrounding vegetal cells mirrors ingressing PMCs, suggesting coordinated morphogenetic roles.