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#developmental genetics

3 public questions tagged with this topic.

Drosophila -ll

Bithorax complex controls:

Bithorax complex comprises three protein-coding homeotic genes Ultrabithorax, abdominal-A, and Abdominal-B arranged colinearly along chromosome 3R with cis-regulatory domains bxd, iab-2 to iab-9 controlling parasegment-specific expression from fifth to fourteenth parasegment, corresponding to third thoracic through eighth abdominal segments. Regulatory domains drive tissue-specific patterns activating UBX in T3, abd-A in A1-A4, Abd-B in A5-A8. Deletion transforms posterior segments toward second thoracic identity. Head and anterior thorax specification relies on Antennapedia complex, while antenna formation depends on homothorax and Distal-less, distinct from BX-C control, illustrating functional subdivision of homeotic clusters along anteroposterior axis for segment identity determination.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: Bithorax complex controls thoracic and abdominal segment identities.

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Drosophila -ll

Thoracic segment identity gene:

Thoracic segment identity depends on Antennapedia complex genes Sex combs reduced, Antennapedia, and adjacent Ultrabithorax. Antennapedia specifies second thoracic segment by promoting leg and dorsal mesothorax formation, while repressing head development programs in trunk. In Antepedia mutants, T2 transforms toward antenna or head fate; in gain-of-function, antenna becomes leg. Nanos governs posterior abdominal development, Gurken and Pipe control dorsal-ventral polarity, unrelated to thoracic identity. Therefore Antennapedia serves as thoracic selector gene interpreting segmentation cues and executing thoracic morphogenetic programs via activation of thoracic-specific effectors like apterous, vestigial, and decapentaplegic signaling modulators required for leg patterning and wing induction.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: Antennapedia as thoracic selector gene - second thoracic segment identity.

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Drosophila -ll

Wingless (Wg) is homologous to vertebrate:

Wingless gene product is secreted glycoprotein lipid-modified by Porcupine acyltransferase, orthologous to vertebrate Wnt1 originally identified as integration site for mouse mammary tumor virus and as wingless in Drosophila. Wg binds Frizzled and co-receptor Arrow/LRP, inhibiting beta-catenin destruction complex allowing Armadillo nuclear translocation activating target genes. Vertebrate Wnt family controls axis patterning, limb development, and stem cell maintenance. Sonic Hedgehog belongs to Hh family, Notch to distinct juxtacrine receptor family, BMP to TGF-beta family, making Wnt specific homolog. Conservation underscores central role of Wg/Wnt signaling in segment polarity, midbrain-hindbrain organizer formation, and oncogenesis mechanisms.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Wingless homologous to vertebrate Wnt1 - Frizzled signaling pathway.

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