Vitellogenin (VTG or less popularly known as VG) (from latin vitellus = yolk and gener = to produce) is a synonymous term for the gene and the expressed protein. The protein molecule is classified as a glyco-lipo-protein, having properties of a sugar, fat and protein. Vitellogenin is an egg yolk precursor protein expressed in females of fish, amphibians, reptiles (including birds), and insects. In the presence of estrogenic endocrine disruptive chemicals (EDCs), male fish can express the Vg gene in a dose dependent manner. Vg gene expression in male fish can be used as a molecular marker of exposure to estrogenic EDCs.

Vitellogenin and honey bees

Honey bees deposit vitellogenin molecules in fat bodies in their abdomen and heads. The fat bodies apparently acts as a food storage reservoir. The glycolipoprotein vitellogenin has additional functionality as it acts as an antioxidant to prolong Queen bee and forager lifespan as well as a hormone that affects future foraging behavior. ^[1] The health of a honey bee colony is dependent upon the vitellogenin reserves of the nurse bees - the foragers having low levels of vitellogenin. As expendable laborers, the foragers are fed just enough protein to keep them working their risky task of collecting nectar and pollen. Vitellogenin levels are important during the nest stage and thus influence honey bee worker division of labor.

A nurse bee's vitellogenin titer that developed in the first four days after emergence, affects its subsequent age to begin foraging and whether it preferentially forages for nectar or pollen. If young workers are short on food their first days of life, they tend to begin foraging early and preferentially for nectar. If they are moderately fed, they forage at normal age preferentially for nectar. If they are abundantly fed, immediately after emergence, their vitellogenin titer is high and they begin foraging later in life, preferentially collecting pollen. Pollen is the only available protein source for honey bees.

Vitellogenin and juvenile hormone feedback loop

For the majority of the investigated insect species it has been documented that juvenile hormone stimulates the transcription of the vitellogenin genes and the consequent control of vitellogenin production (cf. Engelmann, 1983; Wyatt and Davey, 1996). ^{[2] [3]}

The vitellogenin expression is part of a regulatory feedback loop that enables vitellogenin and juvenile hormone to mutually suppress each other. Vitellogenin and juvenile hormone likely work antagonistically in the honey bee to regulate the honey bees development and behavior. Suppression of one leads to high titers of the other. ^[4]

It is likely that the balance between vitellogenin and juvenile hormone levels is also involved in swarming behavior. ^[5]

Juvenile hormone levels drop in honey bee colonies pre-swarming and it is expected that vitellogenin levels would therefore rise. One may surmise, that swarming bees would want to pack along as much vitellogenin as possible to extend their lifespan and to be able to quickly build a new nest.

References

• Wheeler, Diana E.; Kawooya, John K. Purification and characterization of honey bee vitellogenin Archives of Insect Biochemistry and Physiology 1983-1995; Volume 14, Issue 4, May 1990
• Vitellogenin Gene Expression in Male Fathead Minnow as an Indicator of Exposure to Endocrine Disrupting Chemicals (EDC) in an Aquatic Environment 2006. at EPA.gov
• Amdam, G. V.; Norberg, K.; Omholt, S. W.; Kryger, P.; Lourenço, A. P.; Bitondi, M. M. G.; Simões, Z. L. P. Higher vitellogenin concentrations in honey bee workers may be an adaptation to life in temperate climates Insectes Sociaux Volume 52, Number 4 / November, 2005
• Seehuus, Siri-Christine; Norberg, Kari; Gimsa, Ulrike; Krekling, Trygve and Amdam, Gro V. Reproductive protein protects functionally sterile honey bee workers from oxidative stress PNAS, Vol.103 No.4; January 24, 2006
• Nelson, C. Mindy; Ihle, Kate E.; Fondrk, M. Kim; Page Jr., Robert E.; Amdam, Gro V. The Gene vitellogenin Has Multiple Coordinating Effects on Social Organization PLoS Biology Vol. 5, No. 3 March 6, 2007
• Corona, Miguel; Velarde, Rodrigo A.; Remolina, Silvia; Moran-Lauter, Adrienne; Wang, Ying; Hughes, Kimberly A.; and Robinson, Gene E. Vitellogenin, juvenile hormone, insulin signaling, and queen honey bee longevity PNAS April 24, 2007 vol. 104 no. 17 pages 7128-7133

See also

• glycoprotein
• lipoprotein

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