Chromosome assignments of genes for rat ceruloplasmin (CP) and metallothionein (MT)

Metallothionein isoforms (I+II and III) and interleukin-6 in the hippocampus of old rats: may their concomitant increments lead to neurodegeneration?

Metallothionein (MT)-III isoform is a brain metal-binding protein that, like the MT-I + II isoform, binds zinc with high affinity. In the young-adult age, MT-III isoform increases during transient stress while MT-I + II isoform decreases, suggesting compensatory phenomena between the two isoforms and a protective role of MT-III against oxidative damage. This role may be questioned during ageing, because the stress-like condition is chronic in ageing due to high persistent levels of interleukin-6. In the present study, high expression of MT-III and MT-I + II genes (examined by RT-PCR and in situ hybridisation) was found in the hippocampus of old rats. These results indicate that a large amount of free zinc ions can be sequestered by MT isoforms, leading to impaired zinc-dependent functions in the ageing brain. In addition, zinc (tested with the Timm's method) was found to be low in mossy fibres from the old hippocampus. As this method tests bound and unbound zinc, we also investigated free zinc ion bioavailability based on the ratio active thymulin/total thymulin. We found that zinc ion bioavailability was low in old rats, together with increased interleukin-6 mRNA, high expression of both MT isoforms and reduced number of synapses whose function is zinc-dependent, in the old hippocampus. The results indicate that concomitant increments of both MT isoforms may provoke detrimental synergistic effects leading to reduced free zinc ion bioavailability for synapses. As a consequence, compensatory phenomena between MT isoforms may not occur in the old hippocampus due to chronic stress-like condition elicited by high persistent levels of interleukin-6.

An integrated genetic linkage map with 1,137 markers constructed from five F2 crosses of autoimmune disease-prone and -resistant inbred rat strains

The rat (Rattus norvegicus) is an important experimental model for many human diseases including arthritis, diabetes, and other autoimmune and chronic inflammatory diseases. The rat genetic linkage map, however, is less well developed than those of mouse and human. Integrated rat genetic linkage maps have been previously reported by Pravenec et al. (1996, Mamm. Genome 7: 117-127) (500 markers mapped in one cross), Bihoreau et al. (1997, Genome Res. 7: 434-440) (767 markers mapped in three crosses), Wei et al. (1998, Mamm. Genome 9: 1002-1007) (562 markers mapped in two crosses), Brown et al. (1998, Mamm. Genome 9: 521-530) (678 markers mapped in four crosses), and Nordquist et al. (1999, Rat Genome 5: 15-20) (330 markers mapped in two crosses). The densest linkage map combined with a radiation hybrid map, reported by Steen et al. (1999, Genome Res. 9: AP1-AP8), includes 4736 markers mapped in two crosses. Here, we present an integrated linkage map with 1137 markers. We have constructed this map by genotyping F2 progeny of five crosses: F344/NHsd x LEW/NHsd (673 markers), DA/Bkl x F344/NHsd (531 markers), BN/SsN x LEW/N (714 markers), DA/Bkl x BN/SsNHsd (194 markers), and DA/Bkl x ACI/SegHsd (245 markers). These inbred rat strains vary in susceptibility/resistance to multiple autoimmune diseases and are used extensively for many types of investigation. The integrated map includes 360 loci mapped in three or more crosses. The map contains 196 new SSLP markers developed by our group, as well as many SSLP markers developed by other groups. Two hundred forty genes are incorporated in the map. This integrated map should allow comparison of rat genetic maps from different groups and thereby facilitate genetic studies of rat autoimmune and related disease models.

Mapping of the genes for rat endothelin receptor type A (ETAR) and type B (ETBR) to chromosomes 19 and 15 respectively

Chromosomal assignments of the genes for rat endothelin receptor type A (ETAR) and type B (ETBR) were performed by analysing somatic cell hybrid DNAs with the polymerase chain reaction (PCR) using primers specific for rat ETAR and ETBR genes. The genes for ETAR and ETBR were assigned to rat chromosomes 19 and 15 respectively.