Establishment and maintenance of parasegmental compartments

Area of Science:

• Developmental Biology
• Genetics
• Cell Biology

Background:

• Metazoan embryos develop repeating segmental units early in embryogenesis.
• In Drosophila, parasegments are the earliest segmental units, defined by fushi-tarazu (ftz) and even-skipped (eve) gene expression stripes.
• The precise mechanisms by which ftz and eve establish parasegment boundaries and regulate parasegment loss remain unclear.

Purpose of the Study:

• To elucidate how fushi-tarazu and even-skipped gene expression levels define parasegment boundaries.
• To investigate the cellular mechanisms underlying parasegment loss when ftz or eve function is compromised.
• To explore potential parallels between Drosophila parasegment development and vertebrate metameric unit establishment.

Main Methods:

• Analysis of Drosophila embryos with altered fushi-tarazu and even-skipped expression levels.
• Microscopic observation and characterization of cellular behaviors during parasegment formation and loss.
• Investigating the sequential cellular events including delamination and apoptosis.

Main Results:

• Parasegment widths are determined by the relative levels of fushi-tarazu and even-skipped at stripe junctions, leading to alternating wide and narrow parasegments.
• Significant shifts (≥30%) in gene expression levels result in enlarged parasegments persisting and reduced parasegments being eliminated.
• Parasegment loss occurs via a three-step process: cell delamination, apoptosis of delaminated cells, and subsequent apoptosis of remaining inappropriate surface cells.

Conclusions:

• Relative gene expression levels of fushi-tarazu and even-skipped are critical for defining parasegment width and integrity.
• A defined sequence of cellular events, including delamination and apoptosis, mediates the loss of malformed parasegments.
• These findings suggest conserved molecular and cellular mechanisms may govern metameric unit formation in vertebrates.