Regulation of avidin accumulation by prostaglandins in chick oviduct culture

Avidin expression during chick chondrocyte and myoblast development in vitro and in vivo: regulation of cell proliferation

Avidin is a major [(35)S]methionine-labeled protein induced by bacterial lipopolysaccharide (LPS) and interleukin 6 (IL-6) in cultured chick embryo myoblasts and chondrocytes. It was identified by N-terminal sequencing of the protein purified from conditioned culture medium of LPS-stimulated myoblasts. In addition, avidin was secreted by unstimulated myoblasts and chondrocytes during in vitro differentiation; maximal expression being observed in differentiated myofibers and hypertrophic chondrocytes. In developing chick embryos, immunohistochemistry revealed avidin in skeletal muscles and growth plate hypertrophic cartilage. Avidin was secreted into culture as a biologically active tetramer. Exogenous avidin added to the medium of proliferating chondrocytes progressively inhibited cell proliferation, whereas addition of avidin to differentiating chondrocytes in suspension allowed full cell differentiation. No toxic effects for the cells were observed in both culture conditions. Western blots of samples from cytosolic extracts using alkaline-phosphatase-conjugated streptavidin showed three biotin-containing proteins. Acetyl-CoA carboxylase was identified by specific antibodies. Based on these data, we propose that avidin binds extracellular biotin and regulates cell proliferation by interfering with fatty acid biosynthesis during terminal cell differentiation and/or in response to inflammatory stimuli.

DDE-induced eggshell thinning in birds: effects of p,p'-DDE on the calcium and prostaglandin metabolism of the eggshell gland

1. The focus of this review is the effects and mechanism of action of p,p'-DDE on eggshell formation in birds. Inhibition of prostaglandin synthesis in the eggshell gland mucosa is a probable mechanism for p,p'-DDE-induced eggshell thinning. 2. The duck is sensitive to p,p'-DDE-induced eggshell thinning but the domestic fowl is not, and studies comparing the two species in regard to the calcium and prostaglandin metabolism of the eggshell gland have shown that eggshell thinning induced by p,p'-DDE in ducks is accompanied by reduced activity of prostaglandin synthetase, reduced levels of prostaglandin E2, and reduced uptake of 45Ca by the eggshell gland mucosa. The content of calcium, bicarbonate, chloride, sodium, and potassium are also reduced in the eggshell gland lumen in ducks exhibiting eggshell thinning. None of these effects are seen in the domestic fowl. 3. Inhibition of prostaglandin synthesis is a specific effect of p,p'-DDE. The detrimental effects of p,p'-DDE on the eggshell gland seem to be unique when comparing the compound with structurally related substances, i.e., similar treatment regimens with o,p'-DDE, p,p'-DDT, o,p'-DDT, and p,p'-DDD do not cause eggshell thinning in ducks. Neither do they inhibit prostaglandin synthesis in the eggshell gland mucosa. 4. Administration of other compounds that do inhibit prostaglandin synthesis, e.g., indomethacin, does cause the same effects as those seen with p,p'-DDE, i.e., eggshell thinning and the described effects on the calcium and prostaglandin metabolism of the eggshell gland.

Molecular cloning and nucleotide sequence of chicken avidin-related genes 1-5

Using avidin cDNA as a hybridisation probe, we detected a gene family whose putative products are related to the chicken egg-white avidin. Two overlapping genomic clones were found to contain five genes (avidin-related genes 1-5, avr1-avr5), which have been cloned, characterized and sequenced. All of the genes have a four-exon structure with an overall identity with the avidin cDNA of 88-92%. The genes appear to have no pseudogenic features and, in fact, two of these genes have been shown to be transcribed. The putative proteins share a sequence identity of 68-78% with avidin. The amino acid residues responsible for the biotin-binding activity of avidin and the bacterial biotin-binding protein, streptavidin, are highly conserved. Since avidin is induced in both a progesterone-specific manner and in connection with inflammation, these genes offer a valuable tool to study complex gene regulation in vivo.

Progesterone stimulates prostaglandin synthesis in eggshell gland mucosa of estrogen-primed chickens

1. Prostaglandins may be involved in calcium translocation in the avian shell gland, since indomethacin, administered at the beginning of shell formation, reduces eggshell thickness as well as 45Ca-uptake and prostaglandin synthesis by a homogenate of eggshell gland mucosa. 2. The stimulus for calcium transport in the shell gland during shell formation remains unknown. 3. The present study was undertaken to investigate the effects of progesterone on prostaglandin formation by the eggshell gland mucosa of the domestic fowl. 4. Progesterone significantly stimulated synthesis of PGF2 alpha, PGE2 and TXB2 by eggshell gland mucosa homogenate. 5. Progesterone treatment also induced the synthesis of the biotin-binding protein, avidin. 6. A microsomal fraction prepared from the eggshell gland mucosa had a high affinity for binding PGE2. 7. Progesterone treatment reduced the KD value of this binding without affecting the maximal number of binding sites. 8. Progesterone did not change the total calcium content of shell gland mucosa. 9. The role progesterone plays in prostaglandin formation and calcium transport in the eggshell gland mucosa is discussed.

Influence of chlorinated hydrocarbons, Hg2+ and methyl-Hg+ on steroid hormone receptors from eggshell gland mucosa of domestic fowls and ducks

A series of chlorinated hydrocarbons were investigated for their ability to inhibit the binding of tritiated progesterone, dexamethasone and testosterone to their respective cytoplasmic receptors, prepared from the eggshell gland mucosa of the domestic fowl. o,p'-DDE and toxaphene were most potent in inhibiting the binding of progesterone and testosterone to their receptors, while p,p'-DDE was most potent in inhibiting the binding of dexamethasone. The effect of the latter compound on dexamethasone binding was biphasic. There were significant differences between ducks and domestic fowls in the dissociation constant (KD) and maximal number of binding sites (Bmax) for several of the steroid hormones. No effect of steroid binding was observed in the p,p'-DDE-treated ducks that were laying thin-shelled eggs. Some metals were also tested for their ability to inhibit progesterone binding. Hg2+ was most potent (IC50 = 5.8 x 10(-5) M) in this respect, while Cd2+, Pb2+ and Al3+ inhibited the binding only when administered in very high concentrations (10(-3) M). Me-Hg+ was less potent than Hg2+. It is concluded that chlorinated hydrocarbon pesticides may interact with several different steroid hormone receptors. These findings are discussed in relation to some reproductive and other hormonal disturbances observed in birds and mammals.