Src proteins/src genes: from sponges to mammals

Area of Science:

• Evolutionary Biology
• Molecular Biology
• Genomics

Background:

• The marine sponge Suberites domuncula, from the ancient phylum Porifera, has at least five Src-type protein genes.
• This is more than in Caenorhabditis elegans or Drosophila melanogaster, which have two each.

Purpose of the Study:

• To investigate the evolutionary history and gene structure of Src-type proteins in the marine sponge Suberites domuncula.
• To understand the ancestral state of Src genes in the common metazoan ancestor.

Main Methods:

• Full characterization of three S. domuncula Src proteins (SRC1SD, SRC2SD, SRC3SD).
• Comparative sequence analysis of S. domuncula Src proteins and orthologs from other species.
• Identification of Src homology 2 (SH2) and 3 (SH3) domains in the S. domuncula EST database.
• Full sequencing of two S. domuncula src genes (src1SD and src2SD).
• Comparative analysis of intron positions across various metazoan src genes.

Main Results:

• S. domuncula Src proteins show lower homology (68-71%) compared to freshwater sponge orthologs (82-85%).
• Identification of SH2 and SH3 domains unrelated to protein tyrosine kinases (PTKs), suggesting ancestral multidomain structure.
• src1SD has six introns, src2SD has one intron before the SH2 domain, which is conserved in position.
• A single conserved intron position before the SH2 domain across all metazoan src genes suggests its presence in the ancestral gene.
• Vertebrate src genes share conserved intron positions, indicating a common origin.

Conclusions:

• Multiple Src-type genes likely existed in the Urmetazoa (hypothetical metazoan ancestor).
• The ancestral src gene was likely a multidomain protein including SH3, SH2, and tyrosine kinase (TK) domains.
• The intron preceding the SH2 domain and the TK domain exon are highly conserved across Metazoa, providing insights into early gene organization.