3.2. Phylogenetic analysis of SS in vertebrates
Based on the previously cloned and newly identified SS precursor
sequences, a phylogenetic tree was constructed. As shown in Fig. 3,
the vertebrate SS precursors are divided into five clades. Each clade
contains some known orthologous genes (Tostivint et al. (2004) and
see below), indicating that phylogenetic analysis could be helpful to
identify the orthologs among SS genes. In this phylogenetic tree, the
elephant shark SS-like precursor is clustered within the SS2 clade.
Because the elephant shark SS2-like precursor is only a partial
sequence precluded in the present phylogenetic analysis, the
clustering of the elephant shark SS-like precursor within the SS2
clade probably indicates that these precursors are more phylogenetically
related to SS2 rather than its orthologous relationship with the
bony fish SS2. The presence of an SS-like precursor in another
cartilaginous fish (little skate) containing [Pro2]SS-14 also supports
the speculation that the shark SS-like gene is likely descended from
SS2.
Adding the sequence data of other members of the SS gene family
(UII or URP) as an out-group makes the sequence data so divergent
that even sequence alignments cannot be performed. Moreover, most
peptide hormone precursors are short and poorly conserved, which
makes phylogenetic tree analysis unsuitable to address the evolutionary
relationships among homologs (Conlon and Larhammar
2005). To reveal the evolutionary history of multiple SS genes
identified in the present study, we further performed genomic
synteny analysis.
3.2. Phylogenetic analysis of SS in vertebratesBased on the previously cloned and newly identified SS precursorsequences, a phylogenetic tree was constructed. As shown in Fig. 3,the vertebrate SS precursors are divided into five clades. Each cladecontains some known orthologous genes (Tostivint et al. (2004) andsee below), indicating that phylogenetic analysis could be helpful toidentify the orthologs among SS genes. In this phylogenetic tree, theelephant shark SS-like precursor is clustered within the SS2 clade.Because the elephant shark SS2-like precursor is only a partialsequence precluded in the present phylogenetic analysis, theclustering of the elephant shark SS-like precursor within the SS2clade probably indicates that these precursors are more phylogeneticallyrelated to SS2 rather than its orthologous relationship with thebony fish SS2. The presence of an SS-like precursor in anothercartilaginous fish (little skate) containing [Pro2]SS-14 also supportsthe speculation that the shark SS-like gene is likely descended fromSS2.Adding the sequence data of other members of the SS gene family(UII or URP) as an out-group makes the sequence data so divergentthat even sequence alignments cannot be performed. Moreover, mostpeptide hormone precursors are short and poorly conserved, whichmakes phylogenetic tree analysis unsuitable to address the evolutionaryrelationships among homologs (Conlon and Larhammar2005) นี้จะเปิดเผยประวัติวิวัฒนาการของยีน SS หลายพบในการศึกษา เราเพิ่มเติมทำออกsynteny การวิเคราะห์
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