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#vertebrates

25 public questions tagged with this topic.

Eye Lens Induction -l

Which of the following correctly describes the effect of Pax6 loss in vertebrates?

Pax6 serves as master control gene for eye morphogenesis across vertebrates. It sits at top of regulatory hierarchy, directly activating downstream genes including Sox2, Six3, Maf and crystallins in lens, retina and cornea. Null homozygous mutants in mice, rats and humans display anophthalmia or severely reduced eye rudiments because optic vesicle fails to maintain retinal identity and ectoderm cannot achieve lens competence. Even retina, iris and cornea development collapses. Dosage sensitivity explains why haploinsufficiency still permits small eye while complete loss eliminates entire eye field, not just lens alone.

Ref: NCBI Bookshelf, Molecular Biology of the Cell, Chapter 21: Pax6 master regulator - anophthalmia phenotype in mutants.

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Eye Lens Induction -l

Which of the following is the primary inducer in vertebrate eye lens formation?

During classic Spemann-type transplantation, contact between neuroectoderm-derived optic vesicle and overlying head surface ectoderm initiates lens development. The optic vesicle secretes BMP4 and FGFs that upregulate Pax6 and Sox2 in competent ectoderm, driving thickening into lens placode and subsequent invagination. Removal of the vesicle blocks lens formation in competent regions, while trunk ectoderm lacks competence and cannot respond. This inductive interaction remains the textbook example of tissue interaction establishing eye primordia, initiating crystallin expression and highlighting sequential signals from endoderm and neural plate.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Eye development - optic vesicle induction and lens formation.

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Eye Lens Induction -ll

What is the main function of retinoic acid in eye development?

Retinoic acid signaling synthesized by retinal pigment epithelium via Raldh1-3 enzymes plays pivotal role in retinal differentiation patterning. Retinoic acid gradient along dorsal-ventral axis regulates expression of Tbx5, Vax2, and Cyp26 to specify dorsal-ventral retinal identity, promote photoreceptor differentiation, and stimulate neurite outgrowth. RA also induces Pax2 in optic stalk and supports vascular development. It does not primarily induce lens which depends on BMP-FGF, nor optic vesicle formation which precedes RA, nor cornea formation dependent on surface ectoderm, but fine-tunes retinal progenitor competence and patterning.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: Retinoic acid role in retinal dorsal-ventral patterning and differentiation.

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Eye Lens Induction -ll

Which tissue is competent to form the lens in vertebrates?

Only anterior head ectoderm overlying optic vesicle region possesses competence to respond to lens inductive signals and form lens. Competence is conferred by prolonged expression of Pax6, Six3, Sox2, and Otx2 while trunk and non-head ectoderm lacks these factors and fails to transcribe crystallins even when transplanted beneath optic vesicle. Any ectodermal cell is not competent, neural crest forms craniofacial mesenchyme not lens, endoderm forms gut tube. Classic transplantation of optic vesicle to trunk ectoderm yields no lens, whereas head ectoderm transplanted elsewhere can form lens, defining restricted competent territory for induction.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: Head ectoderm competence restricted to Pax6-positive territory.

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Regeneration -l

Which of the following describes regeneration in vertebrates?

Vertebrate regeneration is not limited to embryonic stages but re-engages developmental programs via integrated genetic and cellular mechanisms operating asexually without gamete formation. It involves wound epidermis formation, immune modulation, dedifferentiation of mature cells into progenitors, activation of resident stem cells, and proliferation forming blastema or compensatory growth. Gene regulation is central: Wnt, FGF, BMP, Hedgehog, and retinoic acid pathways are redeployed with epigenetic remodeling and positional memory. This distinguishes regeneration from reproduction, which produces new organism, and explains why mammals regenerate liver and digit tips while salamanders regenerate whole limbs.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Vertebrate regeneration - genetic regulation and cellular mechanisms.

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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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Fertilization in mammals-lll

Zona pellucida analogous to invertebrate:

In comparative reproductive biology mammalian zona pellucida is functional homolog of vitelline envelope surrounding eggs of echinoderms, amphibians and other vertebrates. Both are extracellular matrices of sulfated glycoproteins that mediate species-specific sperm binding, induce acrosome reaction, establish block to polyspermy after fertilization-induced modifications. Jelly coat lies outside vitelline envelope in sea urchins providing chemotactic peptides, whereas chorion denotes tough outer layer of insect and fish eggs, micropyle is narrow canal for sperm entry. Thus vitelline envelope is direct evolutionary and structural analogue to mammalian zona, preserving conserved elements like ZP domain proteins for gamete recognition across phyla.

Ref: Gilbert, Developmental Biology, Chapter 8: Zona pellucida as mammalian vitelline envelope homolog in fertilization.

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