Sea sponges (phylum Porifera) represent the likely first true multicellular animal life on Earth. As such, sponges have the potential to show us the most fundamental aspects of tissue structure and maintenance, including biomineralization, an innate immune system, and an extracellular matrix, among other aspects.
Jackson et al., in last week’s issue of Science, fill in some of the gaps regarding the paleogenetics of ion transport, pH regulation and biomineralization, by looking at the sponge precursor to the alpha-carbonic anhydrase gene family. Their paper, Sponge Paleogenomics Reveals an Ancient Role for Carbonic Anhydrase in Skeletogenesis, taking us a step further in understanding the earliest ancestor of today’s animals.
In a commentary in the same issue, Taylor et al. put these findings and others like them into the proper context, writing about the Evolutionary Insights from Sponges. They write:
In addition to their evolutionary significance, sponges are also notable for their intimate symbioses with microorganisms. Dense and diverse communities of microbial symbionts can constitute almost half of the total sponge volume, contributing appreciably to the host’s metabolism and biochemical repertoire. A. willeyana, the Caribbean sponge Aplysina fistularis (see the figure), and many other sponges host substantial microbial communities. Many symbionts are specific to particular sponges, and these associations are maintained by the transmission of symbionts through sponge eggs and larvae. It thus seems likely that symbiotic microorganisms contributed to the evolutionary success of their ancient hosts. The inferred presence in the ancestral metazoan of various cell receptors, an innate immunity system, and an extra-cellular matrix–all of which contribute to the recognition of microbes by a host organism–suggest that the genetic infrastructure necessary for establishing microbial symbioses was present in the earliest sponges.
Of course, I’m more interested in the potential insights into origins of cell-cell and cell-matrix interactions, than on the origins of biomineralization, but it’s still interesting!
- Jackson DJ, Macis L, Reitner J, Degnan BM, Wörheide G. Sponge paleogenomics reveals an ancient role for carbonic anhydrase in skeletogenesis. Science. 2007 Jun 29;316(5833):1893-5.
- Taylor MW, Thacker RW, Hentschel U. Evolutionary insights from sponges.
. 2007 Jun 29;316(5833):1854-5.