CREATURES, Hormones, Proteins, Reproduction, Silkworm
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Vitellogenin is a precursor of egg yolk that transports protein and some lipid from the liver through the blood to the growing oocytes where it becomes part of the yolk. Normally, it is only found in the blood or hemolymph of females…

Vitellogenin (VTG or less popularly known as VG) (from Latin vitellus, yolk, and genero, I produce) is a precursor of egg yolk that transports protein and some lipid from the liver through the blood to the growing oocytes where it becomes part of the yolk. Normally, it is only found in the blood or hemolymph of females, and can therefore be used as a biomarker in vertebrates of exposure to environmental estrogens which stimulate elevated levels in males as well as females.

“Vitellogenin” is a synonymous term for the gene and the expressed protein. The protein product is classified as a glycolipoprotein, having properties of a sugar, fat and protein. It belongs to a family of several lipid transport proteins.

Vitellogenin is an egg yolk precursor found in the females of nearly all oviparous species including fish, amphibians, reptiles, birds, most invertebrates, and monotremes. Vitellogenin is the precursor of the lipoproteins and phosphoproteins that make up most of the protein content of yolk. In the presence of estrogenic endocrine disruptive chemicals (EDCs), male fish can express the gene in a dose dependent manner. This gene expression in male fish can be used as a molecular marker of exposure to estrogenic EDCs.

Function

Vitellogenin provides the major egg yolk protein that is a source of nutrients during early development of egg-laying (oviparous) vertebrates and invertebrates. Although vitellogenin also carries some lipid for deposition in the yolk, the primary mechanism for deposition of yolk lipid is instead via VLDLs, at least in birds and reptiles.

Vitellogenin precursors are multi-domain apolipoproteins (proteins that bind to lipids to form lipoproteins), that are cleaved into distinct yolk proteins. Different vitellogenin proteins exist, which are composed of variable combinations of yolk protein components; however, the cleavage sites are conserved.[citation needed]

Components

In vertebrates, a complete vitellogenin is composed of:

  • an N-terminal signal peptide for export,
  • and four regions that can be cleaved into yolk proteins, these are:
    • lipovitellin-1,
      • Vitellogenin-1 and vitellogenin-2 (the most abundant of the three vitellogenins) are two high molecular weight glycoproteins (200kDa) containing 4 domains, lipovitellin-1, lipovitellin-2, phosvitin and a peptide of 40 amino-acids called YGP40, which are specifically released after intraoocytic proteolytic processing by cathepsin D, an endogenous aspartic protease (Retzek et al., 1992). The genes coding these two proteins are overexpressed by more than 40 fold and 30 fold, respectively, in the liver of sexually mature hens (Bourin et al., 2012). In contrast, vitellogenin 3 is a smaller glycoprotein (37kDa) lacking lipovitellins and YGP40 domains but containing phosvitin. Vitellogenin-derived phosvitins sequester and store calcium, iron and other cations from the bloodstream to relocate them to the yolk, to further provide minerals and trace elements for the developing embryo. Similarly, lipovitellins are lipid-bound proteins, which function is to fulfill lipid requirements for embryo growth.
      • α and β Lipovitellins. These are lipoproteins, and the two forms differ from one another principally in the amount of protein-bound phosphorus they contain and in their amino acid composition. The relative proportion of α and β lipovitellins differs according to the breed of the hen. The lipovitellins constitute the main non-aqueous constituent of the yolk and are therefore an important component of the yolk granules.
        • https://www.sciencedirect.com/topics/medicine-and-dentistry/lipovitellin
    • phosvitin,
      • This is the second-most plentiful constituent of the yolk granules. It is a phosphoprotein and has many of the physical properties of a poly-electrolyte. It binds iron and so is used as an iron store for the developing embryo.
        • https://www.sciencedirect.com/topics/medicine-and-dentistry/lipovitellin
      • Phosvitin is one of the egg (commonly hen’s egg) yolk phosphoproteins known for being the most phosphorylatedprotein found in nature. Phosvitin isolation was first described by Mecham and Olcott in the year 1949. Recently it has been shown that disordered secondary structure of phosvitin orchestrates nucleation and growth of biomimetic bone like apatite.
        • Joubert, F. J.; Cook, W. H. (1958). “Preparation And Characterization Of Phosvitin From Hen Egg Yolk”. Canadian Journal of Biochemistry and Physiology. 36 (4): 399–408. doi:10.1139/o58-045. PMID 13511246.
        • Clark, Richard C. (1980). “Relative and total abundance of constituent phosphoproteins from hen phosvitin in egg yolk”. International Journal of Biochemistry. 12 (4): 651–653. doi:10.1016/0020-711x(80)90021-x. PMID 7428998.
        • Samaraweera, Himali (Sep 2011). “Egg Yolk Phosvitin and Functional Phosphopeptides—Review”. Journal of Food Science. 76 (7): R143–R150. doi:10.1111/j.1750-3841.2011.02291.x. PMID 21806612.
        • Taborsky, George (1963). “Interaction Between Phosvitin and Iron and Its Effect on a Rearrangement of Phosvitin Structure”. Biochemistry. 2 (2): 266–271. doi:10.1021/bi00902a010. PMID 13980103.
        • Jung, Samooel; et al. (Dec 2012). “The functional property of egg yolk phosvitin as a melanogenesis inhibitor”. Food Chemistry. 135 (3): 993–998. doi:10.1016/j.foodchem.2012.05.113. PMID 22953815.
        • Allerton, Samuel E.; Perlmank, Gertrude E. (Oct 1965). “Chemical Characterization of the Phosphoprotein Phosvitin”. The Journal of Biological Chemistry. 240 (10): 3892–3898. PMID 5891575.
        • Sarem, Melika; Lüdeke, Steffen; Thomann, Ralf; Salavei, Pavel; Zou, Zhaoyong; Habraken, Wouter; Masic, Admir; Shastri, V. Prasad (2017-07-17). “Disordered Conformation with Low Pii Helix in Phosphoproteins Orchestrates Biomimetic Apatite Formation”. Advanced Materials. 29 (35): 1701629. doi:10.1002/adma.201701629. ISSN 0935-9648. PMID 28714191.
    • lipovitellin-2,
      • Vitellogenin-1 and vitellogenin-2 (the most abundant of the three vitellogenins) are two high molecular weight glycoproteins (200kDa) containing 4 domains, lipovitellin-1, lipovitellin-2, phosvitin and a peptide of 40 amino-acids called YGP40, which are specifically released after intraoocytic proteolytic processing by cathepsin D, an endogenous aspartic protease (Retzek et al., 1992). The genes coding these two proteins are overexpressed by more than 40 fold and 30 fold, respectively, in the liver of sexually mature hens (Bourin et al., 2012). In contrast, vitellogenin 3 is a smaller glycoprotein (37kDa) lacking lipovitellins and YGP40 domains but containing phosvitin. Vitellogenin-derived phosvitins sequester and store calcium, iron and other cations from the bloodstream to relocate them to the yolk, to further provide minerals and trace elements for the developing embryo. Similarly, lipovitellins are lipid-bound proteins, which function is to fulfill lipid requirements for embryo growth.
        • https://www.sciencedirect.com/topics/medicine-and-dentistry/lipovitellin
    • von Willebrand factor type D domain (YGP40).

N-terminal lipid transport domain

Vitellogenin lipid transport domain, N-terminal
Identifiers
SymbolVitellogenin_N
PfamPF01347
InterProIPR001747
SMARTSM00638
PROSITEPS51211
SCOP21llv / SCOPe / SUPFAM
OPM superfamily254
OPM protein1lsh
showAvailable protein structures:

This particular domain represents a conserved region found in several lipid transport proteins, including vitellogenin, microsomal triglyceride transfer protein and apolipoprotein B-100.

Vesicle trafficking

This particular domain, the Vitellogenin lipid transport domain, is also found in the Microsomal triglyceride transfer protein (MTTP) and in Apolipoprotein B. It aids cell trafficking and export of cargo.[citation needed]

Microsomal triglyceride transfer protein (MTTP)

Microsomal triglyceride transfer protein (MTTP) is an endoplasmic reticulum lipid transfer protein involved in the biosynthesis and lipid loading of apolipoprotein B. MTTP is also involved in the late stage of CD1d trafficking in the lysosomal compartment, CD1d being the MHC I-like lipid antigen presenting molecule.

Apolipoprotein B

Apolipoprotein B can exist in two forms: B-100 and B-48. Apolipoprotein B-100 is present on several lipoproteins, including very low-density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and low density lipoproteins (LDL), and can assemble VLDL particles in the liver.

Apolipoprotein B-100 has been linked to the development of atherosclerosis.

ApoB is ancestrally universal to all animals, as homologs are found in choanoflagellates. The insect homolog is called apolipophorin I/II.

  • Huebbe P, Rimbach G (August 2017). “Evolution of human apolipoprotein E (APOE) isoforms: Gene structure, protein function and interaction with dietary factors”. Ageing Research Reviews. 37: 146–161. doi:10.1016/j.arr.2017.06.002. PMID 28647612. S2CID 3758905.

Human proteins containing this domain

APOB (see native LDL-ApoB structure at 37°C on YouTube); MTTP;

  • Kumar V, Butcher SJ, Öörni K, Engelhardt P, Heikkonen J, et al. (2011) Three-Dimensional cryoEM Reconstruction of Native LDL Particles to 16Å Resolution at Physiological Body Temperature. [1]

Honey bees

Honey bees deposit vitellogenin molecules in fat bodies in their abdomen and heads. The fat bodies apparently act 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.

  • Oliver, Randy (August 2007). “Fat Bees Part 1”. American Bee Journal.[verification needed]

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.[citation needed]

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.

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).

  • Engelmann F (1983). “Vitellogenesis controlled by juvenile hormone”. In Downer RG, Laufer H (eds.). Endocrinology of Insects. New York: Alan R. Liss. pp. 259–270.
  • Wyatt GR, Davey KG (1996). “Cellular and Molecular Actions of Juvenile Hormone. II. Roles of Juvenile Hormone in Adult Insects”. Advances in Insect Physiology Volume 26. Vol. 26. pp. 1–155. doi:10.1016/S0065-2806(08)60030-2. ISBN 9780120242269.

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.

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

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.[citation needed]

Juvenile hormones (JHs) are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. The first discovery of a JH was by Vincent Wigglesworth. JHs regulate development, reproduction, diapause, and polyphenisms. The chemical formula for juvenile hormone is C18H30O3{\displaystyle {\ce {C_18H_30O_3}}}.

  • Riddiford, L. M. (1994). “Cellular and molecular actions of juvenile hormone I. General considerations and premetamorphic actions”. Advances in Insect Physiology. 24: 213–274. doi:10.1016/S0065-2806(08)60084-3. ISBN 9780120242245.
  • Watt, G. R.; Davey, K. G. (1996). “Cellular and Molecular Actions of Juvenile Hormone. II. Roles of Juvenile Hormone in Adult Insects”. Advances in Insect Physiology. 26: 1–155. doi:10.1016/S0065-2806(08)60030-2. ISBN 9780120242269.
  • Nijhout, H. F. (1994). Insect Hormones. Princeton: Princeton University Press.

In insects, JH (formerly neotenin) refers to a group of hormones, which ensure growth of the larva, while preventing metamorphosis. Because of their rigid exoskeleton, insects grow in their development by successively shedding their exoskeleton (a process known as molting).

Juvenile hormones are secreted by a pair of endocrine glands behind the brain called the corpora allata. JHs are also important for the production of eggs in female insects.

  • In insect physiology and anatomy, the corpus allatum (plural: corpora allata) is an endocrine gland that generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata (an allatectomy) can cause an immature larva to pupate at its next molt, resulting in a miniature adult. Similarly, transplantation of corpora allata from a young larva to a fully mature larva can greatly extend the larval stage, resulting in an equivalent to gigantism.
  • In many Diptera species, the corpus allatum is fused with the corpus cardiacum, forming a “ring gland”, also known as Weismann‘s ring.
  • In Lepidoptera species, the corpus allatum acts as a release site for prothoracicotropic hormone which is generated by the brain.
    • Insect Hormones, page 13, by H. Fredrik Nijhout, 1994, Princeton University Press
    • Prothoracicotropic hormone (PTTH) was the first insect hormone to be discovered.The chemical symbol for prothoracicotropic hormone is (C64H102N16O19S2). It was originally described simply as “brain hormone” by early workers such as Stefan Kopeć (1922) and Vincent Wigglesworth (1934), who realized that ligation of the head of immature insects could prevent molting or pupation of the body region excluded from the head if the ligation was performed before a critical age in the lifestage was reached. After a certain point the ligation had no effect and both sections of the insect would molt or pupate. However, implantation of a conspecific brain to a sessile ligated abdomen or an abdomen under diapause would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects.
    • Later it was established that the insect brain produces a number of hormones, but the hormone which was the cause of the observations made by Kopeć and Wigglesworth was prothoracicotropic hormone. PTTH is secreted by a neurohemal organ, the corpus cardiacum (in some insects the corpus allatum secretes PTTH) which is actually a discrete structure posterior to the brain. PTTH is released in response to environmental stimuli and as its name implies PTTH acts on the prothoracic glands, which respond by releasing molting hormone (an ecdysteroid) into the haemolymph. Molting hormone stimulates the molting process.
      • Chapman, R.F. 1998. The Insects: Structure and Function. 4th edition, Cambridge University Press.
      • Klowden, M.J. 2007. Physiological Systems in Insects. 2nd edition, Academic Press.
      • Unfortunately neurohemal doesn’t have a Wikipedia page. Another site says this: Nerve cells are secretory, for responses to the nerve impulses that they propagate depend upon the production of chemical transmitter substances, or neurotransmitters, such as acetylcholine and norepinephrine (noradrenaline), which are liberated at nerve endings in minute amounts and have only a momentary action. It has been established, however, that certain specialized nerve cells, called neurosecretory cells, can translate neural signals into chemical stimuli by producing secretions called neurohormones. These secretions, which are often polypeptides (compounds similar to proteins but composed of fewer amino acids), pass along nerve-cell extensions, or axons, and are typically released into the bloodstream at special regions called neurohemal organs, where the axon endings are in close contact with blood capillaries. Once released in this way, neurohormones function in principle similar to hormones that are transmitted in the bloodstream and are synthesized in the endocrine glands.
        • https://www.britannica.com/science/hormone/The-hormones-of-vertebrates
      • The distinctions between neural and endocrine regulation, no longer as clear-cut as they once seemed to be, are further weakened by the fact that neurosecretory nerve endings are sometimes so close to their target cells that vascular transmission is not necessary. There is good evidence that hormonal regulation occurs by diffusion in plants and (although here the evidence is largely indirect) in lower animals (e.g., coelenterates), which lack a vascular system.
        • https://www.britannica.com/science/hormone/The-hormones-of-vertebrates
      • Neurohormone, any of a group of substances produced by specialized cells (neurosecretory cells) structurally typical of the nervous, rather than of the endocrine, system. The neurohormones pass along nerve-cell extensions (axons) and are released into the bloodstream at special regions called neurohemal organs. Neurohormones thus constitute a linkage between sensory stimuli (events or conditions perceived by the nervous system) and chemical responses (endocrine secretions that act on other tissues of the endocrine system or on tissues of other systems, such as those involved with excretion or reproduction).
        • https://www.britannica.com/science/neurohormone
      • The neurohormones in most mammals include oxytocin and vasopressin, both of which are produced in the hypothalamic region of the brain and secreted into the blood by the neurohypophysis (part of the pituitary gland). A second group of neurohormones, called releasing hormones (the first of which was chemically identified in 1969), also originates in the hypothalamus. The members of this group, however, are transmitted within the neural cells to a second locus in the brain, from which they pass in the bloodstream to the adenohypophysis, which also is a part of the pituitary gland. There they either stimulate or inhibit the release of the various adenohypophysial hormones.
      • A third group of neurohormones includes the enkephalins and other endorphins, first observed in 1975 in the course of investigations of the mechanism of action of morphine and other analgesics. The endorphins are effective in relieving pain, a property apparently related to their function as neurotransmitters, passing nerve impulses from one neuron to another. Their neurohormonal activity is manifested by their stimulation of the secretion of somatotropin and vasopressin by an indirect process involving a site (other than the secretory neuron) in the central nervous system. See also endorphin.
        • https://www.britannica.com/science/neurohormone

JH was isolated in 1965 by Karel Sláma and Carroll Williams and the first molecular structure of a JH was solved in 1967.

  • Röller, H.; Dahm, K.H.; Sweeley, C.C.; Trost, B.M. (1967). “The Structure of the Juvenile Hormone”. Angewandte Chemie International Edition. 6 (2): 179–180. doi:10.1002/anie.196701792.

Most insect species contain only juvenile growth hormone (JH) III. To date JH 0, JH I, and JH II have been identified only in the Lepidoptera (butterflies and moths). The form JHB3 (JH III bisepoxide) appears to be the most important JH in the Diptera, or flies. Certain species of crustaceans have been shown to produce and secrete methyl farnesoate, which is juvenile hormone III lacking the epoxide group. Methyl farnesoate is believed to play a role similar to that of JH in crustaceans.

Being a sesquiterpenoid, JH chemical structure differs significantly from the structure of other animal hormones. Some JH analogs have been found in conifers.

  • Rogers, I. H.; J. F. Manville; T. Sahota (April 1974). “Juvenile Hormone Analogs in Conifers. II. Isolation, Identification, and Biological Activity of cis-4-[1′(R)-5′-Dimethyl-3′-oxohexyl]-cyclohexane-1-carboxylic Acid and (+)-4(R)-[1′(R)-5′-Dimethyl-3′-oxohexyl]-1-cyclohexene-1-carboxylic Acid from Douglas-fir Wood”. Canadian Journal of Chemistry. 52 (7): 1192–1199. doi:10.1139/v74-187.

The biosynthesis of JH is similar to that of cholesterol in animals.

Cholesterol biosynthesis has been exhaustively studied in animals. All steps occur in the cytosol. The starting material is citrate, which is exported by the mitochondrion when metabolic fuels are high. It is converted into acetyl-CoA, ADP, CO2, and oxaloacetate by ATP-citrate lyase, together with ATP and CoASH as substrates. Three acetyl-CoAs are converted into HMG-CoA by the cytosolic isoforms of thiolase and 3-hydroxy-3-methylglutaryl-CoA synthase. The HMG-CoA is then reduced by NADPH to mevalonate by HMG-CoA reductase, the rate controlling enzyme of cholesterol biosynthesis. This enzyme has 8 helical domains anchoring it in the Golgi membrane of the ER; the catalytic domain is in the cytosol. It is strongly inhibited by the statins, a class of drugs based on a mold metabolite which, at least at one time, were the largest selling class of drugs in the world. Mevalonate is acted of by a series of 3 kinases to give the highly labile 1,2-diphosphomevalonate-3-phosphate, which is acted on by a lyase to give phosphate, CO2, and isopentenyl diphosphate. Isopentenyl diphosphate isomerase converts the latter to the less stable dimethylallyl diphosphate. Farnesyl diphosphate synthase takes one DMAPP and two IPP to give the C15 metabolite farnesyl diphosphate. There are a large number of additional steps to generate cholesterol from IPP, the ubiquitous precursor of all isoprenoids.[citation needed]

  • Burg, J.S., Espenshade, P.J., 2011. Regulation of HMG-CoA reductase in mammals and yeast. Prog. Lipid Res. 50, 403-410

It appears that the biosynthesis of JH III is identical to that of cholesterol, from production of IPP to FPP, although there appear to be no studies on export of citrate or other metabolites from the mitochondrion into the cytosol, or formation of acetyl-CoA. The enzymes of this pathway were first studied in Manduca sexta, which produces both homoisoprenoid and isoprenoid (JHIII) JHs.

Evolution

Vertebrates started off with a single copy of the vitellogenin gene, and the bird-mammalian and amphilian lineages each experienced duplications that gave rise to the modern genes. With the exception of monotremes, mammals have all their vitellogenin genes turned into pseudogenes, although the region syntenic to bird VIT1-VIT2-VIT3 can still be found and aligned. In monotremes just one of the genes remained functional.

Monotremes are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts, compared to the more common mammalian types. Although they are different from almost all mammals in that they lay eggs, like all mammals, the female monotremes nurse their young with milk. The name monotreme derives from the Greek words μονός (monós ‘single’) and τρῆμα (trêma ‘hole’), referring to the cloaca.

See also

References

  1. “Definition of VITELLOGENIN”.
  2. Robinson, Richard (18 March 2008). “For Mammals, Loss of Yolk and Gain of Milk Went Hand in Hand”. PLOS Biology. 6 (3): e77. doi:10.1371/journal.pbio.0060077. PMC 2267822. PMID 20076706.
  3. Tran, Thi Kim Anh; Yu, Richard Man Kit; Islam, Rafiquel; Nguyen, Thi Hong Tham; Bui, Thi Lien Ha; Kong, Richard Yuen Chong; O’Connor, Wayne A.; Leusch, Frederic D.L.; Andrew-Priestley, Megan; MacFarlane, Geoff R. (May 2019). “The utility of vitellogenin as a biomarker of estrogenic endocrine disrupting chemicals in molluscs”. Environmental Pollution. 248: 1067–1078. doi:10.1016/j.envpol.2019.02.056. hdl:10072/386355. PMID 31091639. S2CID 92464394.
  4. Price, E. R. (2017). “The physiology of lipid storage and use in reptiles”. Biological Reviews. 92 (3): 1406–1426. doi:10.1111/brv.12288. PMID 27348513. S2CID 7570705.
  5. Finn, Roderick Nigel (1 June 2007). “Vertebrate Yolk Complexes and the Functional Implications of Phosvitins and Other Subdomains in Vitellogenins1”. Biology of Reproduction. 76 (6): 926–35. doi:10.1095/biolreprod.106.059766. PMID 17314313.
  6. Thompson, James R.; Banaszak, Leonard J. (July 2002). “Lipid−Protein Interactions in Lipovitellin”. Biochemistry. 41 (30): 9398–409. doi:10.1021/bi025674w. PMID 12135361.
  7. Anderson TA, Levitt DG, Banaszak LJ (July 1998). “The structural basis of lipid interactions in lipovitellin, a soluble lipoprotein”. Structure. 6 (7): 895–909. doi:10.1016/S0969-2126(98)00091-4. PMID 9687371.
  8. Sagiv, Yuval; Bai, Li; Wei, Datsen G.; Agami, Reuven; Savage, Paul B.; Teyton, Luc; Bendelac, Albert (16 April 2007). “A distal effect of microsomal triglyceride transfer protein deficiency on the lysosomal recycling of CD1d”. The Journal of Experimental Medicine. 204 (4): 921–8. doi:10.1084/jem.20061568. PMC 2118556. PMID 17403933.
  9. Olofsson SO, Borèn J (November 2005). “Apolipoprotein B: a clinically important apolipoprotein which assembles atherogenic lipoproteins and promotes the development of atherosclerosis”. Journal of Internal Medicine. 258 (5): 395–410. doi:10.1111/j.1365-2796.2005.01556.x. PMID 16238675. S2CID 19885776.
  10. Huebbe P, Rimbach G (August 2017). “Evolution of human apolipoprotein E (APOE) isoforms: Gene structure, protein function and interaction with dietary factors”. Ageing Research Reviews. 37: 146–161. doi:10.1016/j.arr.2017.06.002. PMID 28647612. S2CID 3758905.
  11. Kumar V, Butcher SJ, Öörni K, Engelhardt P, Heikkonen J, et al. (2011) Three-Dimensional cryoEM Reconstruction of Native LDL Particles to 16Å Resolution at Physiological Body Temperature. [1]
  12. Oliver, Randy (August 2007). “Fat Bees Part 1”. American Bee Journal.[verification needed]
  13. Randy, Oliver (Aug 2007). “Fat Bees – Part 1”. American Bee Journal: 714.
  14. Engelmann F (1983). “Vitellogenesis controlled by juvenile hormone”. In Downer RG, Laufer H (eds.). Endocrinology of Insects. New York: Alan R. Liss. pp. 259–270.
  15. Wyatt GR, Davey KG (1996). “Cellular and Molecular Actions of Juvenile Hormone. II. Roles of Juvenile Hormone in Adult Insects”. Advances in Insect Physiology Volume 26. Vol. 26. pp. 1–155. doi:10.1016/S0065-2806(08)60030-2. ISBN 9780120242269.
  16. Hrassnigg, Norbert; Crailsheim, Karl (2005). “Differences in drone and worker physiology in honeybees (Apis mellifera)” (PDF). Apidologie. 36 (2): 255–277. doi:10.1051/apido:2005015.
  17. Zeng, Zhijiang; Huang, Zachary Y.; Qin, Yuchuan; Pang, Huizhong (1 April 2005). “Hemolymph Juvenile Hormone Titers in Worker Honey Bees under Normal and Preswarming Conditions”. Journal of Economic Entomology. 98 (2): 274–278. doi:10.1603/0022-0493-98.2.274. PMID 15889713. S2CID 198130721.
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Further reading

External links

This article incorporates text from the public domain Pfam and InterPro: IPR001747

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