Faculty & Staff
Joseph C. Bagshaw
Professor
Faculty Listing
Office: Salisbury Laboratories, 210
Phone: +1-508-831-5930
Fax: +1-508-831-5936
jbagshaw@wpi.edu
Educational Background
- B.A., Johns Hopkins University
- Ph.D., University of Tennessee Oak Ridge Graduate School
Research & Teaching Interests
Molecular and developmental biology; Gene structure and function
Research
Research in my laboratory involves a number of aspects of the molecular genetics of crustacea. The crustacea comprise a diverse and interesting phylum, and they provide many opportunities for research. The phylogeny and evolution of the arthropods, including the crustacea, is a topic of great interest and disagreement in which molecular genetics can offer new insights. The brine shrimp, Artemia, is a useful model for cell, developmental and molecular biology, including molecular phylogenetics. Shrimp, prawns, crayfish and lobsters are of commercial value on a global scale, and molecular genetics will contribute to the aquaculture of these valuable species.
Our studies of crustacean gene structure began a number of years ago when we cloned the histone genes of Artemia, the first protein-coding genes ever cloned from a crustacean. We discovered that each repeat unit of histone genes also contains one gene for 55 ribosomal RNA, a curious juxtaposition of genes that has not been reported in any other organism. We subsequently cloned the nucleolar ribosomal RNA genes of Artemia, and we have used both histone and ribosomal genes to study restriction fragment length polymorphisms (RFLPs) in many populations of Artemia. We have also cloned a number of repeated sequence elements from Artemia, one of which is extraordinarily large (14+ kb) and has some characteristics of a transposable element.
The focus of most of our current research is the molecular genetics of the marine shrimp, Penaeus vannamei. The U. S. is one of the world's leading consumers of shrimp, but only a small fraction of this prized seafood is produced in this country. The U. S. is not likely ever to be a major producer of shrimp biomass, but there is a potential market niche for U. S. aquaculture in producing high quality broodstock and larvae, possibly becoming the world's leading supplier. We have been employing molecular probes to measure the degree of genetic diversity (heterozygosity) in captive populations of shrimp. We have cloned both ribosomal RNA genes and histone genes from P. vannamei and shown that both sets of genes are polymorphic in all populations tested, and that the diversity of rRNA genes is restricted in aquacultured shrimp.
The polymorphism we found in the rRNA genes is particularly interesting, because it may have biological significance. Ribosomal RNA genes in all eukaryotes are arranged in tandem repeats of a transcriptional unit that produces the final 1 8S. 5.8S and 28S rRNAs. In P. vannamei, the restriction enzyme Eco Rl divides the rRNA repeat unit into two fragments, one of which is monomorphic in length in every shrimp we have tested. The other fragment is polymorphic, even within individual animals, and the variants differ by nearly equal lengths of 250-280 base pairs. Furthermore, this polymorphic fragment contains the promotor for transcription and the portion of the intergenic spacer immediately upstream from the promotor. In other organisms such as Drosophila and Xenopus this region is known to contain enhancer sequences that increase transcription of the rRNA genes, and in Artemia it contains alternative promotors that are used only in early larval development. If this part of the Penaeus rRNA gene repeat contains either enhancers or alternative promotors, the number of such elements could influence the ability of individual animals to respond to a need for rapid ribosome construction and protein synthesis, for example during early development or vitellogenesis.
We have also isolated from P. vannamei over 80 clones containing repeated DNA sequences, and identified four different simple sequence repeats of two to five bases (microsatellites), one of which is interspersed with a larger tandemly repeated structure of 162-168 bp. This microsatellite sequence has the typical variable number of tandem repeats (VNTR) characteristic; of six independent clones we have sequenced, each has a different number of repeats of the microsatellite sequence. Using a novel primer extension assay, we have found these highly repeated sequences can be used to reveal polymorphism among individual shrimp. Another unusual feature of this sequence is that, on genomic Southern blots, it cross-hybridizes strongly with DNA from a crayfish and a lobster, but not with DNA from other penaeid shrimp.
Homeotic genes, first identified in Drosophila and now known to exist in all metazoa, are major control genes in development. A characteristic sequence found in these genes is the homeobox, which encodes a helix-turn-helix protein motif that binds to specific DNA sequences to regulate gene expression. We have used homeobox genes cloned from Artemia to examine polymorphism of cross-hybridizing genes in P. vannamei. These probes hybridize to many fragments on genomic Southern blots, and one in particular, the Artemia analog of the Drosophila gene Scr (sex combs reduced), reveals fragments that are clearly polymorphic between individual shrimp.