HILL, A.L.*; HILL, M.S; LIUBICICH, D.M.: Insights into early animal evolution: developmental genes in sponges

HOM/Hox genes play vital roles in animal development, and a number of researchers have hypothesized that a primordial-Hox gene or a cluster of two or more genes must exist in sponge genomes. A PCR-based strategy using degenerate oligonucleotide primers was employed to identify important homeobox genes (including HOM/Hox) in marine and freshwater sponges. Several potential HOM/Hox sequences, as well as a Pax gene and an HMG-box gene, have been identified in marine and freshwater sponge species. Using RT-PCR and Northern blot analysis, we have also begun characterizing temporal expression patterns of these genes in free-swimming larvae, recently settled larvae, and young adult sponges. Furthermore, preliminary in situ hybridization experiments have been performed to elucidate spatial expression patterns. Porifera represent the most basal radiation of all extant phyla from the metazoan lineage, and given metazoan monophyly, it is clear that all animal body plans must have arisen from transformations of a single body plan. Sponges may hold important clues to the ancestral state(s) of many genetically controlled developmental programs in the animal kingdom.