Title: Investigating the Role of Oriented Cell Division in Facial Morphogenesis
Adrian Danescu, University of British Columbia
Jaspreet Rekhi, University of British Columbia
Joy Richman (Presenter)
University of British Columbia
Objectives: The mechanisms for facial morphogenesis include proliferation of the mesenchyme that is supported by signals from the epithelium. However additional mechanisms such as cell shape, cell migration and oriented cell division may also be involved. Here we test the hypothesis that localized regions of oriented cell division contribute to the morphogenesis of the frontonasal mass.
Methods: Chicken embryos were fixed at stage 24, 26 and 28, embedded in paraffin and sectioned in the frontal plane. Sections were stained with phospho histone H3 antibody to label mitotic figures. At least 3 embryos per stage were examined and cells from 6 sections per embryo were measured using ImageJ. Angles of cells in metaphase, anaphase or telophase were measured relative to the nasal slit (0-180°). Statistical analysis was carried out using 2-way ANOVA and Tukey's post hoc test (Statistica).
Results: Of the total number of mitotic figures counted, 19% were in metaphase, anaphase or telophase and could be scored. The remainder of cells were either in prophase or dividing in the perpendicular plane. The average angle of scored cells was 90° to the nasal slit and there were no significant differences between the three stages or regions counted. The daughter cells are therefore primarily being added in the mediolateral plane.
Conclusions: Our study suggests that the majority of cell division is oriented in the mediolateral plane but that once chondrogenesis begins at stage 26, new cells are added exclusively to the lateral edges of the frontonasal mass, likely under the stimulation of signals from the nasal slit. Since only 19% of cells could be scored in the frontal plane, we anticipate there will be oriented cell division in the sagittal plane which also contributes to dorsoventral outgrowth. In relation to other mechanisms we have studied such as directed cell movement and general proliferation, oriented cell division plays a minor role in shaping the face.