Some families grow fast and big, while others will always be smaller than average, but what are the genetic causes of these striking growth differences? Curious to find out, Eli Meyer and Donal Manahan from the University of Southern California decided to discover which genes regulate oyster growth and size by investigating the genes expressed in four families of Pacific oyster. Screening 4.5 million cDNAs from the two fast and two slow growing families, the duo identified 34 genes that seem to play a major role in determining whether oyster larvae grow large or small (p. ).
Comparing the gene sequences with databases of known genes, Meyer and Manahan discovered that over half of the genes that affected the size of oyster larvae are involved in protein synthesis and maintenance. Seventeen of the genes turned out to be components of the ribosome, the enormous protein complex that translates mRNA into proteins, but when the duo looked at the expression patterns of these genes, they did not find that the expression levels were altered in the fast growing oysters. Instead, they found imbalances in the expression ratios of individual ribosome components. Meyer and Manahan suspect that oyster families with these imbalances grow more slowly because they waste energy disposing of excessive ribosomal components.
Proteins involved in general protein maintenance also turned up in the fast and slow growing oysters, with faster growing oysters producing peptidylprolyl isomerase, a protein involved in protein folding, while a subunit of the proteasome, which degrades proteins, was expressed significantly more in fast growing larvae than in slower growing larvae.
Looking at other genes whose expression influenced the oyster larvae's sizes, the duo discovered two membrane proteins, caveolin and fasciclin, and a protein that is known to regulate feeding activity in other molluscs known as small cardioactive peptide precursor protein.
Proteins involved in energy metabolism also turned up in Meyer and Manahan's screen, including genes expressing proteins found in the larvae's energy generating mitochondria, and two nuclear genes that have mitochondrial functions.
Having outlined various genes that play a role in determining oyster larvae size, Meyer and Manahan suggest that it may be possible to identify genes that could indicate larval growth rates, as the expression patterns of some of the genes are directly proportional to the mollusc's growth rates.
