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#embryonic segmentation

2 public questions tagged with this topic.

Drosophila -ll

Pair-rule gene mutations affect:

Pair-rule genes initiate periodic pattern where each gene's striped pattern covers every other parasegment; loss removes those parasegments causing deletion of alternate segments observed as missing denticle belts every second segment. Even-skipped mutants delete odd bands, hairy deletes complementary set. Continuous deletion characterizes gap mutants, anterior restriction characterizes head gaps. Pair-rule class links double-segment periodicity to single-segment pattern via segment polarity activation. Mechanism involves combinatorial regulation where gap proteins repress pair-rule stripes in interstripe intervals, creating precise periodic output essential for segmentation clock and metameric organization conserved across arthropod lineages and developmental timing.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Pair-rule mutants affect every other segment - double-segment periodicity.

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Drosophila -ll

Segment polarity genes encode proteins involved in:

Segment polarity genes expressed in fourteen stripes maintain parasegment borders through local signaling. Core module includes wingless secreted from anterior row cells binding Frizzled and hedgehog secreted from posterior row binding Patched, establishing mutually reinforcing loop sustaining engrailed expression. Wingless is Wnt family member, hedgehog belongs to Hedgehog family, both lipid-modified morphogens. Notch governs neurogenesis, BMP patterns dorsal-ventral axis, FGF patterns trachea, not primary for segment polarity. Wnt-Hedgehog reciprocal signaling ensures compartment boundary stability, polarity preservation, and prevents fusion of adjacent parasegments during development and imaginal disc patterning later.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Segment polarity genes - Wingless Wnt and Hedgehog reciprocal signaling loop.

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