Cloning and expression of human nebulin cDNAs and assignment of the gene to chromosome 2q31-q32

We have isolated two nonoverlapping cDNAs encoding human nebulin, a muscle-specific protein. Northern hybridization analysis shows that nebulin is encoded by a huge message at least 25 kb in length. By hybridizing two nonoverlapping cDNAs to DNA isolated from rodent X human cell hybrids, we assign this presumably single-copy gene to human chromosome 2; sublocalization studies indicate that the nebulin gene is on the long arm of the chromosome, in the region 2q31-q32.     

Evidence for chicken GH as the only hypophyseal factor responsible for the stimulation of hepatic 5'-monodeiodination activity in the chick embryo

The influence of an intravenous injection of chicken growth hormone (cGH), a total chicken pars distalis (PD) extract, and a PD extract depleted of cGH by immunoadsorption was studied in the 18-d-old chick embryo. Plasma concentrations of triiodothyronine (T3), thyroxine (T4), and hepatic 5'-monodeiodination (5'-D) activity were measured. An injection of total PD extract raised plasma T3, T4, and 5'-D activity, whereas a PD extract depleted of GH only increased plasma T4. The amount of cGH present in the PD extracts, as measured by homologous cGH radioimmunoassay, increased T3 and raised liver 5'-D, but had no effect on plasma T4. The effect on liver 5'-D was more pronounced with cGH than with a total PD extract, whereas the effect on plasma T3 was somewhat less pronounced. It was concluded that cGH increased the peripheral conversion of T4 into T3 in the chick embryo, whereas a PD extract depleted of cGH was purely thyrotropic. The PD extract also seemed to have 5'-D-suppressing activity.     

The molecular basis for Duchenne versus Becker muscular dystrophy: Correlation of severity with type of deletion

About 60% of both Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) is due to deletions of the dystrophin gene. For cases with a deletion mutation, the "reading frame" hypothesis predicts that BMD patients produce a semifunctional, internally deleted dystrophin protein, whereas DMD patients produce a severely truncated protein that would be unstable. To test the validity of this theory, we analyzed 258 independent deletions at the DMD/BMD locus. The correlation between phenotype and type of deletion mutation is in agreement with the "reading frame" theory in 92% of cases and is of diagnostic and prognostic significance. The distribution and frequency of deletions spanning the entire locus suggests that many "in-frame" deletions of the dystrophin gene are not detected because the individuals bearing them are either asymptomatic or exhibit non-DMD/non-BMD clinical features.     

Human ventricular/slow twitch myosin alkali light chain gene characterization, sequence, and chromosomal location

The gene coding for the human ventricular/slow twitch myosin alkali light chain isoform was isolated and sequenced. It was found to contain a total of seven exons, the last of which is completely 3'-untranslated sequence. Comparison of this gene sequence with that of the various fast twitch skeletal isoform gene sequences revealed that the exon-intron arrangement is conserved within the myosin alkali light chain gene family. In fact the introns are in exactly the same positions within analogous codons. Comparison of the derived amino acid sequence from the human ventricular/slow twitch isoform gene with that of other isoform protein sequences indicated that the protein encoded by this gene is more homologous to the chicken cardiac isoform protein sequence than to any of the other protein sequences. These results indicate that the gene duplication which gave rise to the ventricular/slow twitch and fast twitch isoform genes must have occurred prior to the divergence of mammals and avians. We have also localized the human ventricular/slow twitch isoform gene to the short arm of human chromosome 3. Interestingly the corresponding mouse gene has been mapped to the distal region of mouse chromosome 9 which contains a conserved syntenic group of genes that map to the short arm of human chromosome 3.     

The BMP signaling pathway is required together with the FGF pathway for notochord induction in the ascidian embryo

The 40 notochord cells of the ascidian tadpole invariably arise from two different lineages: the primary (A-line) and the secondary (B-line) lineages. It has been shown that the primary notochord cells are induced by presumptive endoderm blastomeres between the 24-cell and the 64-cell stage. Signaling through the fibroblast growth factor (FGF) pathway is required for this induction. We have investigated the role of the bone morphogenetic protein (BMP) pathway in ascidian notochord formation. HrBMPb (the ascidian BMP2/4 homologue) is expressed in the anterior endoderm at the 44-cell stage before the completion of notochord induction. The BMP antagonist Hrchordin is expressed in a complementary manner in all surrounding blastomeres and appears to be a positive target of the BMP pathway. Unexpectedly, chordin overexpression reduced formation of both primary and secondary notochord. Conversely, primary notochord precursors isolated prior to induction formed notochord in presence of BMP-4 protein. While bFGF protein had a similar activity, notochord precursors showed a different time window of competence to respond to BMP-4 and bFGF. Our data are consistent with bFGF acting from the 24-cell stage, while BMP-4 acts during the 44-cell stage. However, active FGF signaling was also required for induction by BMP-4. In the secondary lineage, notochord specification also required two inducing signals: an FGF signal from anterior and posterior endoderm from the 24-cell stage and a BMP signal from anterior endoderm during the 44-cell stage.     

Thyroid status,but not insulin status,affects expression of avian uncoupling protein mRNA in chicken

The aim of this study was to investigate the hormonal regulation of the avian homolog of mammalian uncoupling protein (avUCP) by studying the impact of thyroid hormones and insulin on avUCP mRNA expression in chickens (Gallus gallus). For 3 wk, chicks received either a standard diet (control group), or a standard diet supplemented with triiodothyronine (T(3); T3 group) or with the thyroid gland inhibitor methimazole (MMI group). A fourth group received injections of the deiodinase inhibitor iopanoic acid (IOP group). During the 4th wk of age, all animals received two daily injections of either human insulin or saline solution. The results indicate a twofold overexpression of avUCP mRNA in gastrocnemius muscle of T3 birds and a clear downregulation (-74%) in MMI chickens compared with control chickens. Insulin injections had no significant effect on avUCP mRNA expression in chickens. This study describes for the first time induction of avUCP mRNA expression by the thermogenic hormone T(3) in chickens and supports a possible involvement of avUCP in avian thermogenesis.     

Introgression of mitochondrial DNA among lineages in a hybridogenetic ant

We report a remarkable pattern of incongruence between nuclear and mitochondrial variations in a social insect, the desert ant Cataglyphis hispanica. This species reproduces by social hybridogenesis. In all populations, two distinct genetic lineages coexist; non-reproductive workers develop from hybrid crosses between the lineages, whereas reproductive offspring (males and new queens) are typically produced asexually by parthenogenesis. Genetic analyses based on nuclear markers revealed that the two lineages remain highly differentiated despite constant hybridization for worker production. Here, we show that, in contrast with nuclear DNA, mitochondrial DNA (mtDNA) does not recover the two lineages as monophyletic. Rather, mitochondrial haplotypes cluster according to their geographical origin. We argue that this cytonuclear incongruence stems from introgression of mtDNA among lineages, and review the mechanisms likely to explain this pattern under social hybridogenesis.