Biomedical subjects

Geert E Reyns

Publications and source records attributed to Geert E Reyns.

4 recordsLinked to original sources

PubMed2006

Thyroid hormone deiodination in birds.

Because the avian thyroid gland secretes almost exclusively thyroxine (T4), the availability of receptor-active 3,3',5-triiodothyronine (T3) has to be regulated in the extrathyroidal tissues, essentially by deiodination. Like mammals and most other vertebrates, birds possess three types of iodothyronine deiodinases (D1, D2, and D3) that closely resemble their mammalian counterparts, as shown by biochemical characterization studies in several avian species and by cDNA cloning of the three enzymes in chicken. The tissue distribution of these deiodinases has been studied in detail in chicken at the level of activity and mRNA expression. More recently specific antibodies were used to study cellular localization at the protein level. The abundance and distribution of the different deiodinases shows substantial variation during embryonic development and postnatal life. Deiodination in birds is subject to regulation by hormones from several endocrine axes, including thyroid hormones, growth hormone and glucocorticoids. In addition, deiodination is also influenced by external parameters, such as nutrition, temperature, light and also a number of environmental pollutants. The balance between the outer and inner ring deiodination resulting from the impact of all these factors ultimately controls T3 availability.

Aging↗

PubMed2005

The dioxin-like PCB 77 but not the ortho-substituted PCB 153 interferes with chicken embryo thyroid hormone homeostasis and delays hatching.

The effects of the dioxin-like polychlorinated biphenyl (PCB) 77 and the ortho-substituted PCB 153 on thyroid hormone availability were investigated during the last week of embryonic development in chicken. High doses of these PCBs (1microg PCB 77 and 20microg PCB 153) were injected into chicken eggs at day 4 of incubation. Blood and tissue samples were collected from day 14 of incubation until 1 day after hatching. We did not observe influences of PCB 153 on thyroid hormone (TH) levels. Treatment with PCB 77, on the other hand, decreased plasma total T(4) concentrations but increased hepatic T(4) levels at day 14 of incubation. Later in development, at stages near the process of hatching, severe decreases of T(4) and T(3) levels were observed in the PCB 77 group, both in plasma and tissues. PCB 77 severely reduced the TH peak that normally coincides with the stage of internal pipping. This reduction was accompanied by a considerable delay in the moment of hatching. We conclude that the dioxin-like PCB 77, but not the ortho-substituted PCB 153, can decrease TH availability towards the end of embryonic development and hence disturb the process of hatching.

Animals↗

PubMed2004

cDNA cloning, functional expression, and characterization of chicken sulfotransferases belonging to the SULT1B and SULT1C families.

A search of the chicken expressed sequence tag (EST) database identified 2 cDNA clones that appeared to represent members of the SULT1B and SULT1C enzyme families. These cDNAs were fully sequenced and found to contain full-length inserts. Phylogenetic analysis of the derived amino acid sequences clearly placed them as the first members of the chicken SULT1B and SULT1C families, respectively, to be identified, and we propose they be named SULT1B1 and SULT1C1. (CHICK)SULT1B1 shares approximately 60% amino acid sequence identity with mammalian SULT1B enzymes, whereas the closest neighbor to (CHICK)SULT1C1 was the ortholog (RAT)SULT1C1, with 68% identity. We cloned these cDNAs into the bacterial expression vectors from the pET series. Transformed Escherichia coli cells strongly expressed the recombinant proteins. Purification of the recombinant enzymes from E. coli was accomplished by a three-step procedure involving ammonium sulfate precipitation, anion exchange chromatography, and affinity chromatography. The purified enzymes displayed subunit molecular weights of approximately 35,000Da on SDS-PAGE, as predicted, and were both able to sulfate a wide range of compounds, including xenobiotics and endogenous substrates such as iodothyronines. Detailed kinetic analysis showed SULT1C1 was more prolific in that it was able to sulfate dopamine, tyramine, and apomorphine, which SULT1B1 was not. 2-Bromophenol was the best substrate for both enzymes. We also raised antibodies against these proteins, which were able to detect the SULTs by ELISA, and which were able to strongly inhibit the recombinant enzymes. This is the first detailed characterization of sulfotransferases from the chicken, and it demonstrates that the avian and mammalian SULT1 enzymes are closely related in both structure and function.

Amino Acid Sequence↗

PubMed2003

Cold-induced enhancement of avian uncoupling protein expression, heat production, and triiodothyronine concentrations in broiler chicks.

The relationships among avian uncoupling protein (avUCP) mRNA expression, heat production, and thyroid hormone metabolism were investigated in 7-14-day-old broiler chicks (Gallus gallus) exposed to a low temperature (cold-exposed chicks, CE) or a thermoneutral temperature (TN). After 7 days of exposure, CE chicks exhibited higher heat production (+83%, P<0.01), avUCP mRNA expression (+20%, P<0.01), and circulating triiodothyronine (T(3)) levels (+104%, P=0.07) for non-statistically different body weights and feed intake between 3 and 7 days of exposure as compared to TN chicks. Plasma thyroxine (T(4)) concentration was clearly decreased in CE chicks (-33%, P=0.06). The lower hepatic inner-ring deiodination activity (-47%) and the higher renal outer-ring deiodination activity (+75%) measured in CE compared to TN chicks could partly account for their higher plasma T(3) concentrations. This study describes for the first time the induction of avUCP mRNA expression by low temperature in chickens, as it has been previously shown in ducklings, and supports the possible involvement of avUCP in avian thermogenesis.

Animals↗