ACL: Advent of Complex Life - MIT Astrobiology Team

David K. Jacobs
Professor
Ecology and Evolutionary Biology
University of California, Los Angeles
621 Charles E. Young Dr. South
Los Angeles CA 90095-1606
Email: djacobs at ucla dot edu
Phone: 310 206-7885

In our effort to examine the evolution of metazoan complexity, we have focused on the development of sensory structures in scyphozoan cnidarians. These jellyfish have eyes, statocysts, and complex neural organization, as well as a relatively comprehensive suite of developmental molecules, which function in sensory, neural and cephalic development in Bilateria. We also have complimentary work in progress on polychaete and acoel flatworm neural and sensory organization, and incipient work on sponges. Thus we are characterizing the similarities in neural and sensory development and cell-type differentiation across the basal Metazoa to better understand the evolution of animal complexity, with particular regard to neural organization.

To date our work on jellyfish involves examination of neural and sensory development and developmental genetics in all three developmental stages: planula, polyp and medusa. In this effort we are using a range of techniques. We employ: TEM to assess ultrastructural details of cell types and neural anatomy; Confocal microscopy to mark and visualize structural components of sensory cells, nerves, and muscles (small neuropeptides, tubulins, and actin, respectively); and additional markers to track cell division (BrdU) and cell death (caspase). In combination these permit a three-dimensional understanding of morphology and developmental process. We then determine the locus of gene expression, using in situ hybridization, of developmental genes know to be involved in the differentiation of sense organs and sensory cell types in bilaterians. These results are also visualized using confocal microscopy, in combination with other markers so that the detailed tissue and cellular context of gene expression can be determined.

As noted in our progress report we currently have a paper in review, a paper now accepted, and several papers in preparation for submission. Submitted work bears on aspects of nervous/sensory system development in the planula, where two discrete sensory “organs” are recognizable: an anterior lateral system that develops first, and an apical sensory system associated with settlement that develops later. There is then a loss from planula to polyp of this entire nervous organization and subsequent development of a new secondary nervous system in the metamorphosis from planula to polyp. Work to be submitted shortly demonstrates that bilaterian genes involved in brain development and the integration of sensory signals are expressed the developing sense organs and sensory nerves of medusae. On a finer scale, we show that particular genes involved in sensory cell differentiation in bilaterians are also involved in differentiation of a subset of sensory cell types in these jellyfish.

In the near term (next 3 months), we are actively engaged in further details of developmental genetics and development during the neural and sensory development of the planula and in polyp tentacles. During this year, we also plan to establish functional assays aimed at determining the morphologic effects of developmental-gene silencing. This will allow us to assess explicit hypotheses of how gene expression influences or determines cell type, as well as how such manipulations of gene expression effect the expression of other regulatory genes involved in the differentiation of sensory nerves, organs, and cell types. The approach will use RNA interference, which has recently proved effective in other cnidarians.

We are also actively pursuing the use of new pyrosequencing technologies (Roche 454) for more effective recovery of developmental genes of interest. UCLA just obtained the 454 system, and we are preparing material for this high-throughput sequencing approaches; we should have preliminary results on its efficacy for our purpose in the next few months.

My student Nagayasu Nakanishi will receive his PhD shortly and we hope to retain him as a NAI funded postdoc for 2009. He has put in an application for funding, and such funding would allow us to develop more work on sponges. Sponges are intriguing in the challenges they present due to the presence of many molecules of interest in sensory development, but the absence of many of the canonical features of nervous systems founding eumetazoans.

I will Instruct an upper division undergraduate/Graduate class at UCLA in Fall 2008 treating issues of Paleontology that are of particular to NAI. In addition in winter 2009 I will teach a graduate seminar at UCLA on Developmental Genetics and Evolution that will be directly applicable to the planned NAI sponsored research.

David Jacobs EEB Faculty Web site