Synaptic scaffolding proteins in rat brain. Ankyrin repeats of the multidomain Shank protein family interact with the cytoskeletal protein alpha-fodrin.

The postsynaptic density is the ultrastructural entity containing the neurotransmitter reception apparatus of excitatory synapses in the brain. A recently identified family of multidomain proteins termed Src homology 3 domain and ankyrin repeat-containing (Shank), also known as proline-rich synapse-associated protein/somatostatin receptor-interacting protein, plays a central role in organizing the subsynaptic scaffold by interacting with several synaptic proteins including the glutamate receptors. We used the N-terminal ankyrin repeats of Shank1 and -3 to search for interacting proteins by yeast two-hybrid screening and by affinity chromatography. By cDNA sequencing and mass spectrometry the cytoskeletal protein alpha-fodrin was identified as an interacting molecule. The interaction was verified by pull-down assays and by coimmunoprecipitation experiments from transfected cells and brain extracts. Mapping of the interacting domains of alpha-fodrin revealed that the highly conserved spectrin repeat 21 is sufficient to bind to the ankyrin repeats. Both interacting partners are coexpressed widely in the rat brain and are colocalized in synapses of hippocampal cultures. Our data indicate that the Shank1 and -3 family members provide multiple independent connections between synaptic glutamate receptor complexes and the cytoskeleton.

Freshwater fish trypanosomes: definition of two types, host control by antibodies and lack of antigenic variation.

Haemoflagellates of the genus Trypanosoma are prevalent in freshwater fishes and are transmitted by leeches as vectors. As demonstrated by sequence comparisons of nuclear small subunit rRNA genes, trypanosomes isolated from several fish species at different localities can be divided into at least 2 closely related types, designated Type A and Type B. A clone derived from a Type A isolate from carp (Cyprinus carpio) was used to study the anti-parasite immune response in specified pathogen-free outbred carp. Infection leads to an initial rise in parasitaemia in the blood followed by a sharp decline in all fish (acute phase). Thereafter, in some carp, parasites become undetectable both in the blood and in internal organs while, in others, low numbers can be found in the blood for up to 1 year (chronic phase). Fish that have controlled an acute infection with the clone are not only protected against an homologous challenge infection, but also against the infection with parasite lines derived from carp in the chronic phase of infection. Passive immunization experiments with IgM purified from serum of recovered carp indicate that the infection is controlled by antibodies. The anti-parasite antibody level in recovered carp remains high for many months although the parasitaemia is controlled at very low levels and the half life of IgM, t1/2 = 22.5 days, is comparatively short. The effective control of trypanosomes in laboratory infections is in contrast to the high prevalence in natural and farmed freshwater fish populations.