RESUMO
Studies of genetically engineered flies and mice have revealed the role that orthologs of the human LIM homeobox LHX4 have in the control of motor-neuron-identity assignment and in pituitary development. Remarkably, these mouse strains, which bear a targeted modification of Lhx4 in the heterozygous state, are asymptomatic, whereas homozygous animals die shortly after birth. Nevertheless, we have isolated the human LHX4 gene, as well as the corresponding cDNA sequence, to test whether it could be involved in developmental defects of the human pituitary region. LHX4, which encodes a protein 99% identical to its murine counterpart, consists of six coding exons and spans >45 kb of the q25 region of chromosome 1. We report a family with an LHX4 germline splice-site mutation that results in a disease phenotype characterized by short stature and by pituitary and hindbrain (i.e., cerebellar) defects in combination with abnormalities of the sella turcica of the central skull base. This intronic mutation, which segregates in a dominant and fully penetrant manner over three generations, abolishes normal LHX4 splicing and activates two exonic cryptic splice sites, thereby predicting two different proteins deleted in their homeodomain sequence. These findings, which elucidate the molecular basis of a complex Mendelian disorder, reveal the fundamental pleiotropic role played by a single factor that tightly coordinates brain development and skull shaping during head morphogenesis.
Assuntos
Processamento Alternativo/genética , Nanismo/genética , Mutação em Linhagem Germinativa/genética , Proteínas de Homeodomínio/genética , Fatores de Transcrição , Sequência de Aminoácidos , Sequência de Bases , Cromossomos Humanos Par 1/genética , Clonagem Molecular , Análise Mutacional de DNA , Nanismo/fisiopatologia , Éxons/genética , Feminino , Genes Dominantes/genética , Humanos , Íntrons/genética , Proteínas com Homeodomínio LIM , Masculino , Dados de Sequência Molecular , Linhagem , Penetrância , Mapeamento Físico do Cromossomo , Hipófise/anormalidades , Sítios de Splice de RNA/genética , RNA Mensageiro/análise , RNA Mensageiro/genética , Rombencéfalo/anormalidades , Alinhamento de Sequência , Crânio/anormalidadesRESUMO
The goal of this study was to develop a method allowing rapid identification of the lactic acid bacteria strains in use in the laboratory (Lactobacillus plantarum NCIMB8826; L. fermentum KLD; L. reuteri 100-23; L. salivarius UCC43321; L. paracasei LbTGS1.4; L. casei ATCC393), based on PCR amplification of 16S RNA coding sequences. First, specific forward oligonucleotides were designed in the variable regions of 16S RNA coding sequences of six Lactobacillus strains. The reverse oligonucleotide was designed in the region where the sequences were homologous for the six strains. The expected size of the amplification product was +/-1000 bp. The specificity of the method was tested on total chromosomal DNA. For five out of the six strains, the amplification of the fragment was strain-specific and the method was directly applicable to colonies. For the strain L. casei ATCC393, an additional argument to the classification of this bacteria in the paracasei group could be proposed. Validation of the developed method was performed by applying it to six Lactobacillus reference strains and to various species of bacteria.
Assuntos
Lactobacillus/classificação , Reação em Cadeia da Polimerase/métodos , Animais , Sequência de Bases , Primers do DNA , DNA Bacteriano/análise , DNA Bacteriano/genética , DNA Ribossômico/análise , DNA Ribossômico/genética , Humanos , Lactobacillus/genética , Lactobacillus/isolamento & purificação , Dados de Sequência Molecular , RNA Ribossômico 16S/genética , Padrões de Referência , Ribotipagem , Especificidade da EspécieRESUMO
In humans, growth hormone receptor (GHR) transcripts exist in two isoforms differing by the retention (GHRfl) or exclusion (GHRd3) of exon 3, whereas in mice GHRfl is solely expressed. This species-specific expression pattern is believed to result from an alternative splice event that, on the basis of conflicting data obtained in humans, has been considered to be tissue-, developmentally, and/or individual-specific. To decipher the molecular basis of this unusual trait, we isolated a 6.8-kilobase fragment spanning exon 3 from individuals expressing GHRfl. Sequence analysis revealed the existence of two 99% identical retroelements flanking this exon. Unexpectedly, individuals expressing GHRd3 displayed a 2.7-kilobase deletion involving exon 3, which most likely results from an ancestral homologous recombination between the two retroelements. The lineage of these retroelements during primate evolution revealed the species specificity of the GHRd3 allele. These findings led us to propose a model underlying the existence of the sole GHRfl allele in most species. Such a retrovirus-mediated alternative splice mimicry, which clears up several as yet unexplained phenomena (i.e. the above-mentioned expression data, the Mendelian inheritance of GHR expression patterns, and the deletion of nonconsecutive exons in growth hormone resistant patients), represents a novel physiological mechanism accounting for protein diversity between and within species.