Dr. Paul A. Roberts

E-Mail: robertsp@bcc.orst.edu, Phone: 541-737-5354, FAX: 541-737-0501, Address: Department of Zoology, Oregon State University, Corvallis, Oregon 97331-2914.

I have these main research interests: 1. Chromosomal evolution and structure in flies. We are especially interested in the distribution and evolution of satellite DNA sequences in constitutive heterochromatin of sibling species of Drosophila melanogaster. For example, ribosomal RNA sequences are usually present in roughly equal amounts on both X and Y chromosomes of Drosophila. We have recently found that in wild-type D. simulans, ribosomal RNA genes are largely absent from the Y. Instead, there is a large block (3000 kilobases) of 240 base-pair repeats from the nontranscribed spacer that ordinarily separates adjacent rRNA genes. There appears to be a phenotypic effect of bristle shortening correlated with the presence of the initiation site for RNA polymerase I transcription on the repeat. Excessive spacer repeats (possibly a new example of "selfish DNA") on the Y may compete for a protein factor essential for normal levels of rDNA transcription on the X.

Optimality theory predicts that the loss of ribosomal RNA genes from the Y chromosome of D. simulans would be countered by natural selection. For example, exchanges between the X and Y, though rare, should occur and any sequences transferred to the Y should be amplified by selection. Curiously, this appears rare in nature. Most races of D. simulans collected from 15 sites on five continents lack significant amounts of rDNA on their Y chromosomes as compared with their X chromosomes.

If, however, the rDNA spacer 240 base-pair repeats are a novel type of selfish DNA as we have postulated, one might expect spacer to vary in amount and location on Y chromosomes from different wild races of D. simulans. So far this prediction is upheld (P. Roberts and A. Lohe, in preparation).

We have mapped a number of simple repeated DNA sequences to heterochromatin of D. melanogaster. About 80 of Y chromosome DNA is composed of nine simple repeated sequences. The Y chromosome, rather than a collection of mutationally degenerate structural genes now appears to be a new construct, primarily the product of amplification of the array of simple DNA sequences.

It is noteworthy that staining and banding patterns of heterochromatic regions correlate with the locations of specific repeated DNA sequences. The basis for cytochemical heterogeneity in banding appears to depend exclusively on the different satellite DNAs present in heterochromatin.

2. Developmental genetics of protein secretion in salivary glands of Drosophila gibberosa. Most studies of salivary gland function have focused on larval glue proteins. We have discovered a species, D. gibberosa, that has very little larval "glue" secretion but massive amounts of prepupal secretion. We suspect that several proteins present in the secretion have a morphogenetic role in development of the imago and are currently attempting to clone, characterize, and determine the role of the genes involved.

3. Gerontology of flies. Using polytene chromosome maps of D. gibberosa we are comparing gene expression in several tissues (salivary gland, midgut, fat body) that have ecdysteroid-programmed cell death. A study of gene activity of Malpighian tubules in larvae, pupae, young, and senescent adults is currently under way.

See also, further description of my work and a more extended list of references in: OSU Research database, and Molecular and Cell Biology Program