Interspecific Introgression in Cetaceans: DNA Markers Reveal Post-F1 Status of a Pilot Whale

Visual species identification of cetacean strandings is difficult, especially when dead specimens are degraded and/or species are morphologically similar. The two recognised pilot whale species (Globicephala melas and Globicephala macrorhynchus) are sympatric in the North Atlantic Ocean. These species are very similar in external appearance and their morphometric characteristics partially overlap; thus visual identification is not always reliable. Genetic species identification ensures correct identification of specimens. Here we have employed one mitochondrial (D-Loop region) and eight nuclear loci (microsatellites) as genetic markers to identify six stranded pilot whales found in Galicia (Northwest Spain), one of them of ambiguous phenotype. DNA analyses yielded positive amplification of all loci and enabled species identification. Nuclear microsatellite DNA genotypes revealed mixed ancestry for one individual, identified as a post-F1 interspecific hybrid employing two different Bayesian methods. From the mitochondrial sequence the maternal species was Globicephala melas. This is the first hybrid documented between Globicephala melas and G. macrorhynchus, and the first post-F1 hybrid genetically identified between cetaceans, revealing interspecific genetic introgression in marine mammals. We propose to add nuclear loci to genetic databases for cetacean species identification in order to detect hybrid individuals.     

Apocytochrome-c competes with pre-ornithine carbamoyl transferase for transport into mitochondria

Apocytochrome c, the cytosolic precursor of cytochrome c, competes with the precursor of ornithine carbamoyltransferase (OCT) for entry into isolated rat liver mitochondria.     

Spermidine and spermine stimulate the transport of the precursor of ornithine carbamoyltransferase into rat liver mitochondria

We have examined the effect of low molecular weight components of the transport mixture generally used for the import of rat liver pre-ornithine carbamoyltransferase by isolated rat liver mitochondria. These studies revealed that spermidine and spermine, at physiological concentrations, stimulate the transport of the precursor of ornithine carbamoyltransferase into mitochondria. This stimulatory effect of spermidine and spermine is concentration-dependent and is completely inhibited at higher than physiological concentrations (20 mM for spermidine and 4 mM for spermine). Magnesium ions, which also have a stimulatory effect, inhibit the stimulatory effect of spermidine.     

In vitro transport of ornithine carbamoyltransferase precursor into rat liver mitochondria using a more homologous medium

The precursor of ornithine carbamoyltransferase can be transported in vitro into rat liver mitochondria using the postmitochondrial supernatant from rat liver, a more homologous medium than the commonly used rabbit reticulocyte lysate. The transport of the precursor in the case of reticulocyte lysate requires a standard translation mixture. In the presence of the postmitochondrial supernatant the same is true. However, when the components of the translation mixture were added individually to the postmitochondrial supernatant, it was found that spermidine or spermine, at physiological concentrations, sufficed for the transport of the precursor of ornithine carbamoyltransferase. The activity of the postmitochondrial supernatant was inactivated by trypsin and slightly decreased by RNase treatment; it was not lost by dialysis or by heating at 100 degrees C.     

The γ subunits of the native GABAA/benzodiazepine receptors

Subunit-specific antibodies to all the γ subunit isoforms described in mammalian brain (γ₁, γ_2S, γ_L, and γ₃) have been made. The proportion of GABA_A receptors containing each γ subunit isoform in various brain regions has been determined by quantitative immunoprecipitation. In all tested regions of the rat brain, the γ₁, and γ₃ subunits are present in considerable smaller proportion of GABA_A receptor than the γ₂ subunit. Immunocytochemistry shows that γ₁ immunoreactivity concentrates in the stratum oriens and stratum radiatum of the CA1 region of the hippocampus. In the dentate gyrus, γ₁ immunoreactivity concentrates on the outer 2/3 of the molecular layer coinciding with the localization of the axospinous synapses of the perforant pathway. In contrast, γ₃ immunoreactivity concentrates on the basket cells and other GABAergic local circuit neurons of the hilus. These cells are also rich in γ_2S. In the cerebellu, γ₁ immunolabeling was localized on the Bergmann glia. The γ_2S and γ_2L subunits are differentially expressed in various brain regions. Thus the γ_2S is highly expressed in the olfactory bulb and hippocampus whereas the γ_2L is very abundant in inferior colliculus and cerebellum, particularly in Purkinje cells, as immunocytochemistry, in situ hybridization and immunoprecipitation techniques have revealed. The γ_2S and γ_2L coexist in some brain areas and cell types. Moreover, the γ_2S and γ_2L subunits can coexist in the same GABA_A receptor pentamer. We have shown that this is the case in some GABA_A receptors expressed in cerebellar granule cells. These GABA_A receptors also have α and β subunits forming the pentamer. Immunoblots have shown that the rat γ₁, γ_2S, γ_2L and γ₃ subunits are peptides of 47, 45, 47 and 44 kDa respectively. Results also indicate that there are aging-related changes in the expression of the γ_2S and γ_2L subunits in various brain regions which suggest the existence of aging-related changes in the subunit composition of the GABA_A receptors which in turn might lead to changes in receptor pharmacology. The results obtained with the various γ subunit isoforms are discussed in terms of the high molecular and binding heterogeneity of the native GABA_A receptors in brain. Special issue dedicated to Dr. Kinya Kuriyama     

Big flies, small repeats: the "Thr-Gly" region of the period gene in Diptera

The region of the clock gene period (per) that encodes a repetitive tract of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran species both within and outside the Drosophilidae. All the non- Drosophilidae sequences in this region are short and present a remarkably stable picture compared to the Drosophilidae, in which the region is much larger and extremely variable, both in size and composition. The accelerated evolution in the repetitive region of the Drosophilidae appears to be mainly due to an expansion of two ancestral repeats, one encoding a Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and asparagine or threonine. In some drosophilids the expansion involves a duplication of the pentapeptide sequence, but in Drosophila pseudoobscura both the dipeptide and the pentapeptide repeats are present in larger numbers. In the nondrosophilids, however, the pentapeptide sequence is represented by one copy and the dipeptide by two copies. These observations fulfill some of the predictions of recent theoretical models that have simulated the evolution of repetitive sequences.