GOODSON, M.S.*; KIMBELL, J.R.; MCFALL-NGAI, M: Characterization of a p53-like protein in the morphogenesis of a light organ symbiosis

The sepiolid squid Euprymna scolopes forms a specific, environmentally transmitted, light organ symbiosis with the luminescent bacterium Vibrio fischeri. On infection with V. fischeri, the juvenile light organ undergoes morphogenic change resulting in the loss of a complex ciliated field dedicated to promoting colonization of the light organ. This field undergoes irreversible apoptosis and regression once the light organ has been colonized for at least 12 h, with complete regression occurring at 4 d post-infection. In other systems, members of the p53 protein family have been shown to induce apoptosis and have a role in development. Using reverse transcription PCR and primers constructed from conserved regions of p53-like protein sequences from Genbank, a 489-bp fragment was amplified from light organ RNA. This fragment matched the DNA-binding domain of p53-like proteins, aligning with the KET gene from the squid, Loligo forbesi, with an identity of 88% and 96% at the nucleotide and protein level, respectively. In common with human p53, the fragment contains residues that form the zinc ion coordination site (C176, H179, C238, C242) that is required for sequence-specific DNA-binding. In addition, residues that have a role in the structural integrity of the domain and DNA contact (R175, G245, R248, R249) are also present. Comparisons of the temporal transcription of this gene during light organ development have been performed using real-time reverse transcription PCR. The spatial and temporal expression of the protein has been compared by using an antibody raised against the expressed DNA fragment. These data suggest a significant role for a squid p53-like protein in light organ morphogenesis. Supported by NSF IBN 9904601 and NIH RR12294 to MM-N.