Vitellin

Definition

A major phosphoprotein and the principal storage protein of egg yolk, derived from vitellogenin and serving as the primary amino acid and lipid reserve for developing embryos. In arthropods, vitellin is sequestered in oocytes during vitellogenesis and is progressively catabolized to nourish the growing embryo through larval or nymphal development.

Etymology

From Latin vitellus (yolk of an egg), diminutive of vitulus (calf), referring to the yellow color of egg yolk.

Example

In the desert locust Schistocerca gregaria, vitellin comprises up to 80% of total yolk protein; during embryogenesis, proteolytic enzymes break down vitellin into free amino acids that are transported to developing tissues, with residual vitellin persisting to sustain the first-instar nymph until feeding begins.

Synonyms

• yolk protein
• lipovitellin

Related Terms

• Vitellogenin
• Vitellogenesis
• Yolk
• oocyte
• embryogenesis
• lipophorin
• oviparity

Usage Notes

Distinguished from vitellogenin, its circulating precursor synthesized in the fat body (in insects) or liver and transported to the ovary. Vitellin refers specifically to the stored form within the oocyte/egg. The term is sometimes used broadly for the major yolk protein fraction, though species-specific isoforms exist (e.g., vitellin A, vitellin B in some lepidopterans). Not to be confused with vitelline membrane, the extracellular envelope surrounding the yolk.