The possible role of metallothionein (MT) in metal homeostasis has been investigated in growing oocytes and eggs of the lizard Podarcis sicula. Chromatographic analysis does not reveal the presence of MT in both ovary and eggs, the only metal-binding proteins detected being represented by high molecular mass components. De novo synthesis of MT could be observed in the ovary of cadmium-treated lizards. A cDNA encoding MT was obtained from the liver of P. sicula by RT-PCR followed by a RACE strategy, using primers designed on consensus motifs of vertebrate MT. In spite of the lack of MT in the ovary of untreated animals, Northern blot analysis demonstrates that the maternal untranslated MT transcript is expressed constitutively in the ovary in all the periods of the ovarian cycle. MT mRNA content increases during the oocyte growth, reaching the highest level in ovulated eggs, concomitantly with the accumulation of zinc and copper. Our findings suggest that maternal MT mRNA accumulates in the egg and is translated sometime during development to cope with the future needs of the growing embryo. The appearance of MT after cadmium treatment suggests that the block that makes the oocytarian MT mRNA untranslatable is removed by the metal.
Accumulation of zinc, copper and metallothionein mRNA in lizard ovary proceeds without a concomitant increase in metallothionein content.
2003
Abstract
The possible role of metallothionein (MT) in metal homeostasis has been investigated in growing oocytes and eggs of the lizard Podarcis sicula. Chromatographic analysis does not reveal the presence of MT in both ovary and eggs, the only metal-binding proteins detected being represented by high molecular mass components. De novo synthesis of MT could be observed in the ovary of cadmium-treated lizards. A cDNA encoding MT was obtained from the liver of P. sicula by RT-PCR followed by a RACE strategy, using primers designed on consensus motifs of vertebrate MT. In spite of the lack of MT in the ovary of untreated animals, Northern blot analysis demonstrates that the maternal untranslated MT transcript is expressed constitutively in the ovary in all the periods of the ovarian cycle. MT mRNA content increases during the oocyte growth, reaching the highest level in ovulated eggs, concomitantly with the accumulation of zinc and copper. Our findings suggest that maternal MT mRNA accumulates in the egg and is translated sometime during development to cope with the future needs of the growing embryo. The appearance of MT after cadmium treatment suggests that the block that makes the oocytarian MT mRNA untranslatable is removed by the metal.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
