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#axis determination

3 public questions tagged with this topic.

C-Elegans Development-l

Which of the following determines the dorsal-ventral axis in C. elegans?

Dorsal-ventral axis in C. elegans originates from early cell contacts rather than diffusible gradients like BMP in vertebrates. At four-cell embryo, AB and P1 touching geometry differentially positions ABp contacting P2 receiving GLP-1 Notch signal involving APX-1, while ABa does not contact P2. This differential contact plus SKN-1, PAR polarity cues orients mitotic spindles via GPR-1/2 G-alpha regulation, positioning descendants dorsally versus ventrally. Physical interaction between AB derivatives and P1 lineage mediated by cadherin HMR-1 and catenin HMP-1 translates contact asymmetry into fate segregation essential for nervous system positioning.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: AB-P1 interaction establishes dorsal-ventral axis via Notch.

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C-Elegans Development-l

Which of the following determines the anterior-posterior axis in C. elegans?

Fertilization entry point defines posterior in C. elegans through centrosome-derived polarity cue. Sperm centrosome enters at one pole, initiating cytoplasmic streaming and actomyosin cortical flows that push PAR-3, PAR-6, PKC-3 and CDC-42 anteriorly, while PAR-1 kinase and PAR-2 RING protein accumulate posteriorly. Microtubule organizing center reorganizes cortex, establishing mutually exclusive domains via phosphorylation feedback. This sperm-position cue creates anterior-posterior axis before first mitosis, dictating unequal cleavage, spindle positioning, and segregation of P-granules and maternal mRNAs essential for asymmetric patterning and early developmental symmetry breaking.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: Axis specification in C. elegans - sperm entry defines posterior and PAR proteins.

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amphibian -ll

The initial dorsal-ventral axis in amphibian embryos is determined by:

Amphibian dorsoventral axis established immediately after fertilization by sperm-induced cortical rotation. Sperm centriole nucleates microtubule array that transports dorsal determinants Dishevelled and GBP with plus-end kinesins to side opposite sperm entry, defining dorsal gray crescent enriched with beta-catenin stabilization factors. Gravity can bias rotation but primary cue is sperm entry point triggering cytoskeletal rearrangement. Genetic programs downstream including Wnt and Nodal refine axis but initial asymmetry derives from sperm entry triggering rotation rather than purely genetic preformation or blastocoel formation random position, linking fertilization site to organizer formation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: Dorsal-ventral axis determination by point of sperm entry.

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