Functional dissection of the Drosophila Kallmann's syndrome protein DmKal-1

BACKGROUND: Anosmin-1, the protein implicated in the X-linked Kallmann's syndrome, plays a role in axon outgrowth and branching but also in epithelial morphogenesis. The molecular mechanism of its action is, however, widely unknown. Anosmin-1 is an extracellular protein which contains a cysteine-rich region, a whey acidic protein (WAP) domain homologous to some serine protease inhibitors, and four fibronectin-like type III (FnIII) repeats. Drosophila melanogaster Kal-1 (DmKal-1) has the same protein structure with minor differences, the most important of which is the presence of only two FnIII repeats and a C-terminal region showing a low similarity with the third and the fourth human FnIII repeats. We present a structure-function analysis of the different DmKal-1 domains, including a predicted heparan-sulfate binding site. RESULTS: This study was performed overexpressing wild type DmKal-1 and a series of deletion and point mutation proteins in two different tissues: the cephalopharyngeal skeleton of the embryo and the wing disc. The overexpression of DmKal-1 in the cephalopharyngeal skeleton induced dosage-sensitive structural defects, and we used these phenotypes to perform a structure-function dissection of the protein domains. The reproduction of two deletions found in Kallmann's Syndrome patients determined a complete loss of function, whereas point mutations induced only minor alterations in the activity of the protein. Overexpression of the mutant proteins in the wing disc reveals that the functional relevance of the different DmKal-1 domains is dependent on the extracellular context. CONCLUSION: We suggest that the role played by the various protein domains differs in different extracellular contexts. This might explain why the same mutation analyzed in different tissues or in different cell culture lines often gives opposite phenotypes. These analyses also suggest that the FnIII repeats have a main and specific role, while the WAP domain might have only a modulator role, strictly connected to that of the fibronectins

Congenital bovine spinal dysmyelination is caused by a missense mutation in the SPAST gene

Bovine spinal dysmyelination (BSD) is a recessive congenital neurodegenerative disease in cattle (Bos taurus) characterized by pathological changes of the myelin sheaths in the spinal cord. The occurrence of BSD is a longstanding problem in the American Brown Swiss (ABS) breed and in several European cattle breeds upgraded with ABS. Here, we show that the disease locus on bovine chromosome 11 harbors the SPAST gene that, when mutated, is responsible for the human disorder hereditary spastic paraplegia (HSP). Initially, SPAST encoding Spastin was considered a less likely candidate gene for BSD since the modes of inheritance as well as the time of onset and severity of symptoms differ widely between HSP and BSD. However, sequence analysis of the bovine SPAST gene in affected animals identified a R560Q substitution at a position in the ATPase domain of the Spastin protein that is invariant from insects to mammals. Interestingly, three different mutations in human SPAST gene at the equivalent position are known to cause HSP. To explore this observation further, we genotyped more than 3,100 animals of various cattle breeds and found that the glutamine allele exclusively occurred in breeds upgraded with ABS. Furthermore, all confirmed BSD carriers were heterozygous, while all affected calves were homozygous for the glutamine allele consistent with recessive transmission of the underlying mutation and complete penetrance in the homozygous state. Subsequent analysis of recombinant Spastin in vitro showed that the R560Q substitution severely impaired the ATPase activity, demonstrating a causal relationship between the SPAST mutation and BSD

Characterization of a human and murine gene (CLCN3) sharing similarities to voltage-gated chloride channels and to a yeast integral membrane protein

We describe the isolation and characterization of a human gene (CLCN3) and its murine homologue (Clcn3) sharing significant sequence and structural similarities with all previously identified members of the voltage-gated chloride channel (ClC) family. This gene is expressed primarily in tissues derived from neuroectoderm. Within the brain, Clcn3 expression is particularly evident in the hippocampus, olfactory cortex, and olfactory bulb. CLCN3 encodes a 760-amino-acid protein that differs by only 2 amino acid residues from the protein encoded by Clcn3. CLCN3 protein also shows a high similarity with GEF1, an integral membrane protein of the yeast Saccharomyces cerevisiae known to be involved in respiration and iron-limited cell growth, and with the predicted protein product of a DNA sequence from the mold Septoria nodorum. This high degree of sequence conservation in very distantly related species such as human and yeast indicates that this gene has retained a fundamental function throughout evolution

Human fetal brain beta-nerve growth factor cDNA: molecular cloning of 5' and 3' untranslated regions

The mRNA of beta-nerve growth factor (beta-NGF) has been demonstrated to be present in the human brain, both in adult and fetal stages of development. However, its complete nucleotide sequence is unknown since a full-length cDNA has yet to be isolated. We report here the cloning and complete analysis of the human fetal brain beta-NGF transcript. cDNA synthesis was performed from total brain RNA and overlapping regions of beta-NGF cDNA were enzymatically amplified and sequenced. The central portion of the cDNA was amplified using primers designed on the known genomic DNA sequence. The 5' and 3' unknown regions were amplified by the anchored polymerase chain reaction (PCR) and by complementary DNA Ends-PCR respectively. The latter method is an original variation of Inverted PCR. The sequenced transcript is very similar to the most common form of beta-NGF mRNA present in the mouse central nervous system. In addition, both the 5' and 3' untranslated regions show a high degree of homology to the corresponding murine sequences

Detection of beta-nerve growth factor mRNA in the human fetal brain

Nerve growth factor (NGF) is a trophic molecule recently demonstrated to interact with different structures in the central nervous system. The expression of the beta-NGF mRNA from human fetal cortices at the 15-16th week of gestational age has been demonstrated and quantitated by polymerase chain reaction amplification of the specific cDNA. beta-NGF mRNA expression in the human brain coincides with the period of active differentiation and synaptogenesis, suggesting that the trophic agent plays a role in the cerebral development