#cell polarity

C-Elegans Development-l

What is the role of PAR proteins in early C. elegans development?

PAR family establishes early embryonic polarity without zygotic transcription relying solely on maternal proteins and sperm cue. PAR-2 RING finger protein recruited posteriorly after sperm centrosome signal suppresses anterior actomyosin contractility via RhoGAP regulation, preventing PAR-3/PAR-6/PKC-3 complex binding posteriorly. PAR-3 scaffolds anterior complex regulating cortical contractility and spindle positioning via GPR-1/2 and LIN-5. Mutual antagonism creates bistable cortical domains translated into cytoplasmic gradients MEX-5 anterior high and PIE-1 posterior high via differential phosphorylation. Conservation from worms to mammals underscores fundamental cortical polarity principle defining axes before gastrulation.

Ref: Kemphues, Annual Review Cell Dev Biology: PAR proteins localize to cortex establishing anterior-posterior polarity.

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C-Elegans Development-l

Which protein plays a key role in establishing anterior-posterior polarity in C. elegans?

PAR proteins are partitioning defective regulators of polarity highly conserved from nematodes to mammals. PAR-3 forms anterior cortical complex with PAR-6 and atypical PKC, anchoring CDC-42 and NMY-2 myosin. PAR-1 MARK kinase and PAR-2 occupy posterior cortex after sperm centrosome signal suppresses anterior contractility and enables posterior recruitment. Mutual exclusion maintained via phosphorylation, so PAR-1 excludes PAR-3 posteriorly and aPKC excludes PAR-1 anteriorly. PAR-3 establishes anterior identity, recruiting centrosome rotation cues and influencing segregation of MEX-5, PIE-1, P-granules, ultimately orchestrating asymmetric division, spindle orientation and embryonic axis formation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: PAR proteins establishing anterior-posterior polarity in early embryo.

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Elegans -ll

What is the function of PAR proteins in C. elegans?

PAR proteins, partitioning defective family identified in C. elegans zygote, establish anterior-posterior polarity essential for asymmetric divisions of P lineage. PAR-3, PAR-6, PKC-3 localize anteriorly, PAR-1, PAR-2 posteriorly after fertilization, driven by sperm centrosome cues and actomyosin flows. This restricts P-granules, PIE-1, SKN-1, MEX-5/6 to posterior blastomere P1, ensuring germline versus somatic divergence. Mutations in par genes randomize AB versus P1 divisions, causing symmetric divisions and loss of endoderm. They do not directly regulate vulval signaling, functioning primarily in early polarity establishment of embryo axis.

Ref: Kemphues et al. 1988; Gilbert, Developmental Biology Chapter 4: PAR proteins establish A-P polarity in C. elegans.

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amphibian -ll

Disheveled protein (Dsh) during amphibian development is initially located at the:

In Xenopus unfertilized egg Dishevelled protein associated with vesicles anchors to vegetal cortex via interaction with VegT-localizing machinery and kinesin motors. Vegetal pole cortex also holds Vg1 and Wnt11 mRNAs. Upon sperm entry, parallel microtubule array assembles and transports Dishevelled vesicles dorsally toward future dorsal side, 30 degrees opposite sperm entry. At dorsal vegetal cortex Dishevelled inhibits Axin-GSK3 complex stabilizing beta-catenin. Animal pole cortex initially depleted of Dishevelled, explaining dorsal determinant transport from vegetal pole to dorsal equator necessary for Gray crescent and Nieuwkoop center establishment.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: Dishevelled localization at vegetal cortex and dorsal translocation.

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