The extracellular thyrotropin receptor domain is not a major candidate for mutations in toxic thyroid nodules.

Constitutive activation of the cyclic adenosine monophosphate (cAMP) cascade by either thyrotropin receptor (TSHR) or gsp mutations is considered to be the major molecular cause of toxic thyroid nodules (TTNs). In a recent study we investigated a consecutive series of 31 TTNs and identified 15 somatic TSHR mutations (n = 14 in exon 10; n = 1 in exon 9) but no mutations in gsp exons 7-10. The purpose of the present study was to determine whether the extracellular TSHR domain would be a candidate for mutations causing TTNs. Therefore, we screened TSHR exons 1-8 in the remaining 16 TTNs without mutations in TSHR exons 9 and 10 and gsp exons 7-10 of our previous study. Except for a known functional polymorphism in exon 1 (Pro 52 Thr) in 2 TTNs and a silent base exchange in exon 7 (187 Asn) in 7 other TTNs no TSHR mutations were identified. To clarify the molecular etiology of TTNs without TSHR or gsp mutations, candidate genes in other steps of the cAMP cascade have to be considered.

Selective recycle of viable animal cells by coupling of airlift reactor and cell settler.

A new system for the perfusion culture of animal cells in suspension is described. It consists of an airlift loop reactor and a settling tank for cell retention. Insufficient nutrient and oxygen supply of the cells in the settling tank was prevented by cooling the cell suspension before entering the settler. As a result, the catabolic activity of the cells in the settler was reversibly reduced. Furthermore, the density gradient induced by cooling caused a liquid motion through the settler. Thus, it was not necessary to pump medium containing shear, sensitive cells. With this simple system, it was possible to prduce 2 to 5 g of antibodies in a 5.4-L reactor in continuous runs of 400 to 600 h. The productivity was increased by a factor of 17 and the cell density was 4 times higher in comparison with the corresponding batch system. The cell retention system was found to have the property of separating viable and nonviable cells. With the increasing perfusion rate, dead cells and debris were preferably washed out. For perfusion rates up to 1.3 d(-1), the retention efficiency of the settler was nearly 100% for viable cells; hence, this system may show advantages at the industrial scale.