Xenopus Bcl-XL selectively protects Rohon-Beard neurons from metamorphic degeneration

Amphibian metamorphosis involves extensive, but selective, neuronal death and turnover, thus sharing many features with mammalian postnatal development. The antiapoptotic protein Bcl-XL plays an important role in postnatal mammalian neuronal survival. It is therefore of interest that accumulation of the mRNA encoding the Xenopus Bcl-XL homologue, termed xR11, increases abruptly in the nervous system, but not in other tissues, during metamorphosis in Xenopus tadpoles. This observation raises the intriguing possibility that xR11 selectively regulates neuronal survival during postembryonic development. To investigate this hypothesis, we overexpressed xR11 in vivo as a green fluorescent protein (GFP)-xR11 fusion protein by using somatic and germinal transgenesis. Somatic gene transfer showed that the fusion protein was effective in counteracting, in a dose-dependent manner, the proapoptotic effects of coexpressed Bax. When GFP-xR11 was expressed from the neuronal β-tubulin promoter by germinal transgenesis we observed neuronal specific expression that was maintained throughout metamorphosis and beyond, into juvenile and adult stages. Confocal microscopy showed GFP-xR11 to be exclusively localized in the mitochondria. Our findings show that GFP-xR11 significantly prolonged Rohon-Beard neuron survival up to the climax of metamorphosis, even in the regressing tadpole tail, whereas in controls these neurons disappeared in early metamorphosis. However, GFP-xR11 expression did not modify the fate of spinal cord motoneurons. The selective protection of Rohon-Beard neurons reveals cell-specific apoptotic pathways and offers approaches to further analyze programmed neuronal turnover during postembryonic development.

Tsetse thrombin inhibitor: Bloodmeal-induced expression of an anticoagulant in salivary glands and gut tissue of Glossina morsitans morsitans

The tsetse thrombin inhibitor, a potent and specific low molecular mass (3,530 Da) anticoagulant peptide, was purified previously from salivary gland extracts of Glossina morsitans morsitans (Diptera: Glossinidae). A 303-bp coding sequence corresponding to the inhibitor has now been isolated from a tsetse salivary gland cDNA library by using degenerate oligonucleotide probes. The full-length cDNA contains a 26-bp untranslated segment at its 5′ end, followed by a 63-bp sequence corresponding to a putative secretory signal peptide. A 96-bp segment codes for the mature tsetse thrombin inhibitor, whose predicted molecular weight matches that of the purified native protein. Based on its lack of homology to any previously described family of molecules, the tsetse thrombin inhibitor appears to represent a unique class of naturally occurring protease inhibitors. Recombinant tsetse thrombin inhibitor expressed in Escherichia coli and the chemically synthesized peptide are both substantially less active than the purified native protein, suggesting that posttranslational modification(s) may be necessary for optimal inhibitory activity. The tsetse thrombin inhibitor gene, which is present as a single copy in the tsetse genome, is expressed at high levels in salivary glands and midguts of adult tsetse flies, suggesting a possible role for the anticoagulant in both feeding and processing of the bloodmeal.

Retinoic acid alters the intracellular trafficking of the mannose-6-phosphate/insulin-like growth factor II receptor and lysosomal enzymes

Previously, we showed that retinoic acid (RA) binds to the mannose-6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R) with high affinity, suggesting that M6P/IGF2R may be a receptor for RA. Here, we show that RA, after 2–3 h of incubation with cultured neonatal-rat cardiac fibroblasts, dramatically alters the intracellular distribution of M6P/IGF2R as well as that of cathepsin B (a lysosomal protease bearing M6P). Immunofluorescence techniques indicate that this change in intracellular distribution is characterized by a shift of the proteins from the perinuclear area to cytoplasmic vesicles. The effect of RA was neither blocked by an RA nuclear receptor antagonist (AGN193109) nor mimicked by a selective RA nuclear-receptor agonist (TTNPB). Furthermore, the RA-induced translocation of cathepsin B was not observed in M6P/IGF2R-deficient P388D1 cells but occurred in stably transfected P388D1 cells expressing the receptor, suggesting that the effect of RA might be the result of direct interaction with M6P/IGF2R, rather than the result of binding to the nuclear receptors. These observations not only support the idea that M6P/IGF2R mediates an RA-response pathway but also indicate a role for RA in control of intracellular trafficking of lysosomal enzymes. Therefore, our observations may have important implications for the understanding of the diverse biological effects of retinoids.

V(D)J recombination is not activated by demethylation of the kappa locus

V(D)J recombination is thought to be regulated by changes in the accessibility of target sites, such as modulation of methylation. To test whether demethylation of the kappa locus can activate recombination, we generated two recombinationally active B cell lines in which the gene for maintenance of genomic DNA methylation, Dnmt1, was flanked with loxP sites. Transduction with a retrovirus expressing both the cre recombinase and green fluorescent protein allowed us to purify recombinationally active cells devoid of methylation. Loss of methylation of the kappa locus was not sufficient to activate recombination, although transcription was activated in one line. It appears that demethylation of the kappa locus is not the rate-limiting step for altering accessibility and thus regulated demethylation does not generate specificity of recombination.

Gestational drive and the green-bearded placenta.

A "green beard" refers to a gene, or group of genes, that is able to recognize itself in other individuals and direct benefits to these individuals. Green-beard effects have been dismissed as implausible by authors who have implicitly assumed sophisticated mechanisms of perception and complex behavioral responses. However, many simple mechanisms for genes to "recognize" themselves exist at the maternal-fetal interface of viviparous organisms. Homophilic cell adhesion molecules, for example, are able to interact with copies of themselves on other cells. Thus, the necessary components of a green-beard effect -- feature, recognition, and response -- can be different aspects of the phenotype of a single gene. Other green-beard effects could involve coalitions of genes at closely linked loci. In fact, any form of epistasis between a locus expressed in a mother and a closely linked locus expressed in the fetus has the property of "self-recognition." Green-beard effects have many formal similarities to systems of meiotic drive and, like them, can be a source of intragenomic conflict.