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#paracrine factor

3 public questions tagged with this topic.

Paracrine Factor

Which of the following is an example of a paracrine factor that functions as a morphogen?

Among cytoskeletal and enzymatic proteins, true paracrine morphogens belong to growth factor families. Activin, a TGF-beta superfamily member, exemplifies paracrine morphogen functioning similar to Xenopus mesoderm induction. Secreted as disulfide-linked dimer, it binds type II and type I serine-threonine kinase receptors causing Smad2/3 phosphorylation, forming complex with Smad4 translocating to nucleus regulating Brachyury, Mix genes. At low concentration induces ventral mesoderm blood, at high concentration induces dorsal organizer notochord. Its activity blocked by Follistatin antagonist, illustrating dosage-dependent positional information analogous to Nodal and BMP roles patterning embryonic fields.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: Activin as TGF-beta morphogen inducing mesoderm in Xenopus.

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Eye Lens Induction -l

Which paracrine factor promotes lens formation in Xenopus embryos?

Xenopus animal cap assays revealed BMP4 as critical paracrine inducer for lens. Optic vesicle and surrounding mesenchyme express BMP4 and BMP7 that diffuse to competent ectoderm, activating SMAD1/5/8 phosphorylation and complex formation with SMAD4, which cooperates with Pax6 and Sox2 to open delta1-crystallin loci. Inhibition of BMP with Noggin or chordin blocks lens marker expression in co-cultures, while recombinant BMP4 restores lens placode formation in absence of optic vesicle. Wnt and Hedgehog antagonize this process, thus BMP provides instructive cue for Xenopus lens specification, distinct from FGF's later role.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: BMP4 promotes lens formation in Xenopus model.

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Eye Lens Induction -ll

Which paracrine factor promotes lens formation in Xenopus embryos?

In Xenopus embryos, bone morphogenetic protein 4 produced by presumptive lens ectoderm and surrounding tissue promotes lens formation independent of optic vesicle at early stages. BMP4 suppresses neural fate, maintains Pax6 and Sox2 in anterior ectoderm, and induces L-Maf and delta-crystallin expression. Retinoic acid patterns retina, Wnt5a regulates morphogenesis, JAK-STAT not lens inductive. Overexpression of BMP4 in competent ectoderm causes ectopic lens differentiation, Noggin inhibition blocks lens, paralleling chick and mouse data where BMP4 from optic vesicle serves as early paracrine cue driving lens placode specification and crystallin production and growth.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: BMP4 paracrine factor promoting lens formation in Xenopus.

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