Cytoplasm affects embryonic development.

New research provides the best evidence yet that a fertilized egg's nucleus isn't the sole site of control for an embryo's development. Signals emanating from the cell's mitochondria--its power-generating organelles--also appear to influence how an organism grows.

Mitochondria carry their own DNA, which is unrelated to the genetic material in a cell's nucleus. Scientists have been unsure whether mitochondrial DNA has an impact on developmental processes. To investigate this, Zuo-Yan Zhu and his colleagues at the Chinese Academy of Sciences in Wuhan, cloned carp through a technique called nuclear transfer. This method removes the nucleus from one cell and inserts it into an egg that has had its own nucleus removed. However, instead of inserts carp nuclei into carp eggs, Zhu's team inserted them into goldfish eggs. Normal carp have 33 to 36 vertebrae. However, the resulting cloned fish had between 26 and 28 vertebrae--the same number as goldfish--suggesting that mitochondrial DNA in the goldfish eggs had affected the carps' development.

Zhu notes that these results, published in the March Biology of Reproduction, may make researchers think twice about proposals to clone extinct animals using the eggs of living species.--C.B.