Mitochondrial DNA content varies considerably in oocytes, even when collected from the same patient. In the present study, real-time quantitative polymerase chain reaction analysis of 113 unfertilized oocytes obtained from 43 patients revealed an average of 193,000 (range: 20,000 to 598,000) mitochondrial genomes per cell. We compared several groups of oocytes to investigate the relationship between mitochondrial DNA content and fertilizability. The average mitochondrial DNA copy number was significantly lower in cohorts suffering from fertilization failure compared to cohorts with a normal rate of fertilization. In addition, the mitochondrial copy number of oocytes from patients with fertilization failure due to unknown causes was significantly lower than that of oocytes from patients in which IVF failure was due mainly to a severe sperm defect. The lower mtDNA copy number could be due to defective cytoplasmic maturation of oocytes. We conclude that low mitochondrial DNA content, due to inadequate mitochondrial biogenesis or cytoplasmic maturation, may adversely affect oocyte fertilizability.

Our results suggest that low mtDNA content is associated with the impaired oocyte quality observed in ovarian insufficiency.

The mRNA encoding human thyroglobulin has been cloned and sequenced. It is made up of a 8301-nucleotide segment encoding a preprotein monomer of 2767 amino acids, flanked by non-coding 5' and 3' regions of 41 and 106 nucleotides, respectively. This preprotein consists of a leader sequence of 19 amino acids, followed by the sequence of the mature monomer, corresponding to a polypeptide of 2748 amono acids ( M , = 302 773). On its amino-terminal side, 70% of the monomer is characterized by the presence of three types of repetitive units. In contrast, the remaining 30% of the protein is devoid of repetitive units. This last region however shows an interesting homology (up to 64%) with the acetylcholinesterase of Torpedo californica. The sites of thyroid hormones synthesis are clustered at both ends of the thyroglobulin monomer. By contrast, the potential glycosylation sites are scattered along the polypeptide chain.Thyroglobulin is a protein specifically synthesised by the thyroid gland, and constitutes the support for the production of the two thyroid hormones, thyroxine and triiodothyronine [l]. The existence of thyroglobulin was demonstrated a century ago [2], but its structure has been elucidated only recently. It is a dimeric glycoprotein with an M , of 660000, of two identical subunits [3, 41 encoded by a single mRNA with a sedimentation coefficient of 33 S (8500 nucleotides) [5 -71. Thyroglobulin is synthesised by the thyrocyte, then exported to the vesicular lumen where its maturation begins by the iodination of several tyrosine residues, and coupling of some of the iodotyrosine residues [8]. Then, by an endocytotic process, the molecule is absorbed into the thyrocyte where several selective cleavages occur in the lysosomes, resulting in the release of the thyroid hormones, and complete degradation of the rest of the molecule.For a thyroglobulin iodine content of 0.5% (which is rarely attained in man) a maximum of 3.5 hormonal residues per thyroglobulin molecule are formed through a reaction catalyzed by the enzyme thyroid peroxidase [9]. Four hormone-synthesis sites have been described, corresponding to four tyrosine residues in fixed positions [lo-121.The structure of human thyroglobulin seems to be responsible for the specific fixation of iodine, and the production of functional thyroid hormones. Several human pathologies are associated with an abnormal thyroid function. Since the recent demonstration of the implication of a defect in thyroglobulin gene structure in the development of congenital goitre in cattle [13], it is likely that knowledge of the structure of human thyroglobulin mRNA will help to elucidate the structural bases of human thyroid pathologies. We describe here the complete nucleotide sequence of human thyroglobulin mRNA. MATERIALS AND METHODSPreparation and sequencing of DNA cDNA fragments corresponding to human thyroglobulin mRNA were prepared from recombinant plasmids named M1-M4 and B2 -B4 (see Fig. l), as previously described [7, 141. Two additional clones, named B1 (kind gift of ...

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