Cartoon Explaining Nuclear Size (IMAGE) University of California - Berkeley Caption The nucleus of a Xenopus laevis egg cell, represented by the large frog at left, imports the protein importin-alpha (α) at a higher rate than does the nucleus of the smaller egg cells of Xenopus tropicalis (right). Because importin-alpha carries structural materials like lamin that line the inside of the nuclear envelope (NE), X. laevis builds a larger nucleus. Not shown is another protein, ntf2, that regulates the importation of large proteins like importin-alpha. Together, levels of importin-alpha and ntf2 determine the size of the nucleus in the African clawed frog. The squiggly lines inside the bubble cells represent the DNA inside the nucleus. Credit Favian Hernandez Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.