Cell recognition during epithelial fusion

Fusion of epithelial sheets during development and wound healing occurs by a process known as zippering, in which cell surface protrusions called filopodia on two fusing edges interdigitate, thus ‘knitting’ the epithelial sheets together. We have found that during dorsal closure and wound healing in Drosophila embryos, filopodia on the leading edge cells are able to recognise and specifically fuse with matching cells in the opposing epithelium. This filopodial recognition ensures that epithelial fusion occurs accurately. We are currently investigating the molecular basis of this recognition process.

A live Drosophila embryo undergoing dorsal closure. The embryo is expressing red and green fluorescent proteins in defined positions within each segment. Initially the stripes of coloured cells are out of alignment indicating that the fusing epithelia are misaligned. Filopodia search for matching cells in the opposing epithelium and only adhere when they touch a cell of the same colour. This corrects the segment misalignment, ensuring correct morphogenesis.

Mechanisms of epithelial wound repair

Wounding results in damage to epithelia and a major element of wound healing is the restoration of epithelial integrity. In order to better understand the process of epithelial repair, we are studying the healing process following laser wounding of the epidermis of Drosophila embryos. The Drosophila embryo is a useful system for these studies as it is amenable to genetic techniques and live imaging.

A live Drosophila embryo that has been wounded with a laser focused on the epidermis. The embryo is expressing GFP-Moesin in epithelial cells allowing visualisation of the actin cytoskeleton. After wounding, a contractile actin cable forms within the wound edge cells and this pulls the wound closed.

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Actin dynamics during morphogenesis and tissue repair

The cell movements that occur during epithelial morphogenesis and repair are dependent on precise regulation of actin dynamics. While actin dynamics in tissue culture cells has been well-studied, our understanding of actin dynamics in whole organisms is currently poor. The Drosophila embryo is a relatively simple system in which actin dynamics can be readily studied in vivo. We are currently investigating the regulation of two types of actin-based protrusions, lamellipodia and filopodia, in Drosophila embryos.

Filopodial dynamics in a live Drosophila embryo undergoing dorsal closure. This embryo is expressing GFP-Fascin in epithelial cells. Fascin is an actin bundling protein which plays an important role in regulating the formation of filopodia.