[Mutation by deletion-insertion in BRCA-1 gene in three unrelated French breast/ovarian cancer families: possible implication of a mobile element]. / Mutation par délétion-insertion dans le géne BRCA-1 dans trois families françaises non apparentées de cancers du sein et/ou de l'ovaire: possible implication d'un elément mobile.

A new type of mutation by deletion-insertion in BRCA-1 gene is found in three unrelated French breast/ovarian cancer families. Surprisingly, deletion and insertion occurred at the same nucleotide position at the end of exon 11 (3958del5ins4), thus generating a truncated protein. This original mutation consists in a deletion of 5 bp (CTCAG) and in an insertion of 4 different bp (AGGC). Here, we proposed two hypothesis to explain this phenomenom. The first hypothesis is the formation of a hairpin stem-loop structure comprising the mutational site and the sequence corresponding to the duplication insertion 2 nucleotides before the mutation. The second hypothesis, more speculative, consists in an abortive integration of a human mobile element as a human transposon (tigger 1) which involved a deletion of 5 bp during its excision and an insertion of 4 bases corresponding to the 5' extremity of the transposon.

Systematic sequencing of the BRCA-1 coding region for germ-line mutation detection in 70 French high-risk families.

Seventy French high-risk families were screened for germ-line BRCA-1 mutations. The BRCA-1 coding region and the exon-intron boundaries were sequenced, except when pre-screening by PTT revealed a truncated protein in exon 11. Germ-line BRCA-1 mutations were detected in 24% of families. The number of breast and ovarian cancers per family, a relative young age at ovarian cancer diagnosis, and the occurrence of breast and ovarian cancer in the same patient significantly predicted the presence of a BRCA-1 mutation. The low BRCA-1 mutation frequency suggested that some alterations were not detected and some families were probably BRCA-2 or BRCAx carriers.

New mechanism of BRCA-1 mutation by deletion/insertion at the same nucleotide position in three unrelated French breast/ovarian cancer families.

A novel complex mutation consisting of a small deletion/insertion (3958del5ins4) was found in the breast cancer-1 gene (BRCA-1) in three unrelated French breast and/or ovarian cancer families. These mutations occurred at the same nucleotide position of the 3' end of exon 11. The wild-type sequence, CTCAG, was deleted and replaced by AGGC in the three families. The consequence is the generation of a stop codon, TAG, resulting in a truncated protein. We propose two different mechanisms to explain the generation of this complex mutation: (i) the simultaneous occurrence of a deletion and an insertion in a stem-loop structure and (ii) the abortive integration of a human transposable element (Tigger 1) that deleted 5 nucleotides and inserted a 4-nucleotide "scar", corresponding to the 5' extremity of the transposon.

Expression of lactate dehydrogenase, myosin heavy chain and myogenic regulatory factor genes in rabbit embryonic muscle cell cultures.

The expression of myogenic regulatory factors (MRFs), lactate dehydrogenase (LDH) and myosin heavy chains (MyHC), as markers of myogenesis, metabolism and contractility respectively, were investigated during differentiation of rabbit embryonic muscle cells in primary culture. Myf5, MyoD and myogenin mRNAs were abundantly expressed at day 1 of culture. The expression of Myf5 and MyoD mRNA transcripts decreased sharply as myoblasts fused and differentiated into myotubes, whilst myogenin mRNA was maintained throughout the duration of the culture. In contrast, MRF4 mRNA was weakly expressed on day 1 of culture, its expression increased slightly as myoblasts fused and reached a maximum level in 7-day-old cultures containing striated myofibres. The specific activity of LDH increased linearly during myoblast proliferation and fusion. In 7-day-old cultures, LDH-M mRNA (dominant in glycolytic muscles) and LDH-H mRNA (predominant in perinatal and oxidative muscles) represented 38% and 62% of total LDH mRNA respectively. At this stage, immunocytochemical staining with perinatal and adult-type MyHC antibodies showed that embryonic and perinatal MyHC isoforms were expressed in all myotubes, while few of them were stained by type I MyHC antibody. However, none of them expressed adult type II MyHC. The latter results were further supported by RT-PCR analysis of adult-type MyHC mRNA which showed that only the type I MyHC mRNA transcript was expressed. These data were in agreement with those reported in vivo on perinatal rabbit muscles. They differed from those obtained on cultured satellite cells isolated from adult rabbit fast-twitch or slow-twitch muscles which did not express embryonic MyHC, and instead expressed fast- or slow-type MyHC according to their muscle origin. Taken together, these results further suggest that myogenic mononucleated cells express different properties in vitro according to their developmental origin as well as properties related to those of the muscles from which they were isolated.

[Hereditary predispositions to cancer: the genetic diagnosis in practice]. / Prédispositions héréditaires au cancer: le diagnostic génétique en pratique.

Genetic consultations allow to identify families in which an hereditary predisposition to cancer is transmitted. In most cases the gene involved can be studied leading to identification of families members carrying or not the mutation conferring the cancer risk. In this case, cancer risk is more accurately explained and measures, adjusted to the risk, were proposed for early screening of the disease. Capacities to characterize an inherited mutation of the susceptibility gene vary according to our knowledge of the gene, its structure, its function, the kind of mutation(s) and also, the available techniques. The purpose of this paper is to describe the most frequently used techniques for direct or indirect molecular diagnosis of cancer predisposition and to specify, for each of them, the situations where its use seem the fittest. The example of breast cancer hereditary predisposition, where multiple susceptibility genes were identified and other are still unknown, illustrates the various degree of diagnosis that can be proposed and the strategy techniques used according to the gene.

Metabolic and contractile differentiation of rabbit muscles during growth.

1. A study was carried out of post-natal evolution of the oxidative, glycolytic and contractile capacities in various types of rabbit muscle. 2. At birth, muscles are non-differentiated and present very limited metabolic and contractile activity, metabolism is mainly oxidative in all muscles. 3. Although muscular discrimination is manifest from the sixth week after birth, the glycolytic metabolism reaches its maximum capacity only after six to eight weeks. 4. Subsequently, oxidative metabolic capacity steadily decreases until adulthood.