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Eggshell and egg yolk proteins in fish: hepatic proteins for the next generation: oogenetic, population, and evolutionary implications of endocrine disruption.

Arukwe A, Goksøyr A - Comp Hepatol (2003)

Bottom Line: The many molecular events involved in these processes require tight, coordinated regulation that is under strict endocrine control, with the female sex steroid hormone estradiol-17beta in a central role.This has led to the development of specific and sensitive assays for these proteins in fish, and the application of vitellogenin and zona radiata proteins as informative biomarkers for endocrine disrupting effects of chemicals and effluents using fish as test organisms.The genes encoding these important reproductive proteins are conserved in the animal kingdom and are products of several hundred million years of evolution.

View Article: PubMed Central - HTML - PubMed

Affiliation: Great Lakes Institute for Environmental Research, University of Windsor, Ontario, 401 Sunset Avenue, Windsor, N9B 3P4, Canada. arukwe@uwindsor.ca

ABSTRACT
The oocyte is the starting point for a new generation. Most of the machinery for DNA and protein synthesis needed for the developing embryo is made autonomously by the fertilized oocyte. However, in fish and in many other oviparous vertebrates, the major constituents of the egg, i.e. yolk and eggshell proteins, are synthesized in the liver and transported to the oocyte for uptake. Vitellogenesis, the process of yolk protein (vitellogenin) synthesis, transport, and uptake into the oocyte, and zonagenesis, the synthesis of eggshell zona radiata proteins, their transport and deposition by the maturing oocyte, are important aspects of oogenesis. The many molecular events involved in these processes require tight, coordinated regulation that is under strict endocrine control, with the female sex steroid hormone estradiol-17beta in a central role. The ability of many synthetic chemical compounds to mimic this estrogen can lead to unscheduled hepatic synthesis of vitellogenin and zona radiata proteins, with potentially detrimental effects to the adult, the egg, the developing embryo and, hence, to the recruitment to the fish population. This has led to the development of specific and sensitive assays for these proteins in fish, and the application of vitellogenin and zona radiata proteins as informative biomarkers for endocrine disrupting effects of chemicals and effluents using fish as test organisms. The genes encoding these important reproductive proteins are conserved in the animal kingdom and are products of several hundred million years of evolution.

No MeSH data available.


Related in: MedlinePlus

Simplified diagram of estradiol-17β (E2) or E2-mimic stimulated oogenic protein synthesis. Eggshell zona radiata proteins and the egg yolk protein precursor, vitellogenin are synthesized and secreted by the hepatocyte. They are transported in blood to the ovary and incorporated into maturing oocytes in female teleosts.
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Figure 3: Simplified diagram of estradiol-17β (E2) or E2-mimic stimulated oogenic protein synthesis. Eggshell zona radiata proteins and the egg yolk protein precursor, vitellogenin are synthesized and secreted by the hepatocyte. They are transported in blood to the ovary and incorporated into maturing oocytes in female teleosts.

Mentions: Figure 3 shows an order of the molecular mechanisms that lead to the production of Zr-protein and Vtg in the hepatocyte: (1) E2 produced by the ovarian follicular cells in response to GtH I is transported in plasma attached to sex hormone binding globulins (SHBGs: [71-76]) and enters the liver cells by either diffusion or receptor-mediated uptake. The physiological functions of the SHBGs are not fully understood. It is generally believed that these proteins play a role in the regulation of steroid amount available to target tissues and protect steroids from rapid metabolic degradation [77,78]. In addition to their role as sex steroid carriers, it has been proposed that SHBGs are involved in cellular signal transduction that involves nuclear steroid receptors through specific SHBGs membrane receptors in different sex steroid sensitive tissues [for review see, [78]]. (2) In the liver, E2 is retained in target cells by high affinity binding to a specific steroid-receptor protein, the E2-receptor (ER; [80]). In the absence of a ligand the ER is found as a monomer in association with heat shock protein 90 (hsp90). In the ligand binding process, the ER dissociates from hsp90 and usually goes through dimerization prior to translocation of the complex into the nucleus, involving a complex of coregulator proteins (more details on the molecular biology of ER forms and the events taking place in this process can be found in reviews such as [80-83]). (3) The hormone-receptor complex binds tightly in the nucleus at estrogen responsive elements (ERE) located upstream of, or within the estrogen-responsive genes in DNA. (4) This results in the activation or enhanced transcription of Vtg genes and subsequent increase and stabilization of Vtg messenger RNA (mRNA). At present, ERE for Zr-protein genes have not been identified in fish, although their response to E2 is very similar to that of the Vtg genes. Given the speculation that different EREs on the DNA may be temporarily masked by associated proteins, thus resulting in sequential or partial induction of various estrogenic responses [84], it is possible that there may be subtle differences in the responsive elements for Zr-protein and Vtg. (5) Zr-protein and Vtg precursors are synthesized and modified extensively in the rough endoplasmic reticulum (RER); (6) modified Zr-protein and Vtg are secreted into the serum for transport to the ovary. (7) In the ovary, Zr-protein and Vtg are incorporated to serve different functions (see later).


Eggshell and egg yolk proteins in fish: hepatic proteins for the next generation: oogenetic, population, and evolutionary implications of endocrine disruption.

Arukwe A, Goksøyr A - Comp Hepatol (2003)

Simplified diagram of estradiol-17β (E2) or E2-mimic stimulated oogenic protein synthesis. Eggshell zona radiata proteins and the egg yolk protein precursor, vitellogenin are synthesized and secreted by the hepatocyte. They are transported in blood to the ovary and incorporated into maturing oocytes in female teleosts.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC153486&req=5

Figure 3: Simplified diagram of estradiol-17β (E2) or E2-mimic stimulated oogenic protein synthesis. Eggshell zona radiata proteins and the egg yolk protein precursor, vitellogenin are synthesized and secreted by the hepatocyte. They are transported in blood to the ovary and incorporated into maturing oocytes in female teleosts.
Mentions: Figure 3 shows an order of the molecular mechanisms that lead to the production of Zr-protein and Vtg in the hepatocyte: (1) E2 produced by the ovarian follicular cells in response to GtH I is transported in plasma attached to sex hormone binding globulins (SHBGs: [71-76]) and enters the liver cells by either diffusion or receptor-mediated uptake. The physiological functions of the SHBGs are not fully understood. It is generally believed that these proteins play a role in the regulation of steroid amount available to target tissues and protect steroids from rapid metabolic degradation [77,78]. In addition to their role as sex steroid carriers, it has been proposed that SHBGs are involved in cellular signal transduction that involves nuclear steroid receptors through specific SHBGs membrane receptors in different sex steroid sensitive tissues [for review see, [78]]. (2) In the liver, E2 is retained in target cells by high affinity binding to a specific steroid-receptor protein, the E2-receptor (ER; [80]). In the absence of a ligand the ER is found as a monomer in association with heat shock protein 90 (hsp90). In the ligand binding process, the ER dissociates from hsp90 and usually goes through dimerization prior to translocation of the complex into the nucleus, involving a complex of coregulator proteins (more details on the molecular biology of ER forms and the events taking place in this process can be found in reviews such as [80-83]). (3) The hormone-receptor complex binds tightly in the nucleus at estrogen responsive elements (ERE) located upstream of, or within the estrogen-responsive genes in DNA. (4) This results in the activation or enhanced transcription of Vtg genes and subsequent increase and stabilization of Vtg messenger RNA (mRNA). At present, ERE for Zr-protein genes have not been identified in fish, although their response to E2 is very similar to that of the Vtg genes. Given the speculation that different EREs on the DNA may be temporarily masked by associated proteins, thus resulting in sequential or partial induction of various estrogenic responses [84], it is possible that there may be subtle differences in the responsive elements for Zr-protein and Vtg. (5) Zr-protein and Vtg precursors are synthesized and modified extensively in the rough endoplasmic reticulum (RER); (6) modified Zr-protein and Vtg are secreted into the serum for transport to the ovary. (7) In the ovary, Zr-protein and Vtg are incorporated to serve different functions (see later).

Bottom Line: The many molecular events involved in these processes require tight, coordinated regulation that is under strict endocrine control, with the female sex steroid hormone estradiol-17beta in a central role.This has led to the development of specific and sensitive assays for these proteins in fish, and the application of vitellogenin and zona radiata proteins as informative biomarkers for endocrine disrupting effects of chemicals and effluents using fish as test organisms.The genes encoding these important reproductive proteins are conserved in the animal kingdom and are products of several hundred million years of evolution.

View Article: PubMed Central - HTML - PubMed

Affiliation: Great Lakes Institute for Environmental Research, University of Windsor, Ontario, 401 Sunset Avenue, Windsor, N9B 3P4, Canada. arukwe@uwindsor.ca

ABSTRACT
The oocyte is the starting point for a new generation. Most of the machinery for DNA and protein synthesis needed for the developing embryo is made autonomously by the fertilized oocyte. However, in fish and in many other oviparous vertebrates, the major constituents of the egg, i.e. yolk and eggshell proteins, are synthesized in the liver and transported to the oocyte for uptake. Vitellogenesis, the process of yolk protein (vitellogenin) synthesis, transport, and uptake into the oocyte, and zonagenesis, the synthesis of eggshell zona radiata proteins, their transport and deposition by the maturing oocyte, are important aspects of oogenesis. The many molecular events involved in these processes require tight, coordinated regulation that is under strict endocrine control, with the female sex steroid hormone estradiol-17beta in a central role. The ability of many synthetic chemical compounds to mimic this estrogen can lead to unscheduled hepatic synthesis of vitellogenin and zona radiata proteins, with potentially detrimental effects to the adult, the egg, the developing embryo and, hence, to the recruitment to the fish population. This has led to the development of specific and sensitive assays for these proteins in fish, and the application of vitellogenin and zona radiata proteins as informative biomarkers for endocrine disrupting effects of chemicals and effluents using fish as test organisms. The genes encoding these important reproductive proteins are conserved in the animal kingdom and are products of several hundred million years of evolution.

No MeSH data available.


Related in: MedlinePlus