Meeting Abstract

S1.1  Monday, Jan. 4  From Genome to Development in Amphioxus HOLLAND, L.Z.*; SHORT, S.; Univ. of California San Diego; Portsmouth Univ, U.K. lzholland@ucsd.edu

Although gnathostome genomes (mammals, fish) were the first deuterostome genomes sequenced, genomes of most major deuterostome groups have now been sequenced. These include an agnathan (lamprey), ascidian and appendicularian tunicates, a cephalochordate (amphioxus) an echinoderm (sea urchin) and hemichordate. Comparative genomics has answered many questions (e.g. the timing of whole genome duplications) but has also raised awareness of how little is known about how genes direct formation of a functional organism. Heritable traits not directly encoded by the genome (epigenetics) have assumed increased importance in this regard. One such epigenetic phenomenon is alternative splicing. Paired box (Pax) transcription factors are involved in development of such endocrine organs as the thyroid and its homolog, the endostyle (in larval lampreys, tunicates and amphioxus) [Pax2/5/8], the thymus [Pax3/7], pharyngeal endoderm [Pax1/9] and adenohypophysis [Pax4/6]. Alternative splicing can affect the DNA binding domains of Pax factors and/or the c-terminal transactivation and repression domains. Some splice forms are evolutionarily conserved, suggesting vital functions, while others are not. Pax splice forms are differentially expressed during development in both amphioxus and vertebrates. To investigate the importance of Pax isoforms in development, we used antisense morpholino-oligonucleotides (MOs) to knock down function of all isoforms of amphioxus Pax2/5/8 and Pax1/9 as well as that of specific isoforms. Our results show that knockdown of all isoforms of these two genes with an MO complementary to the ATG start codon gives the same phenotype as using a splice-blocking MO to convert the major isoform expressed in early development to a minor one. These results suggest that the minor isoforms may function to modulate function of the major ones and underscore the importance of post-transcriptional mechanisms for gene function.