Early steps in the evolution of multicellularity: deep structural and functional homologies among homeobox genes in sponges and higher metazoans.
The sponge homeobox gene EmH-3 had not been attributed to any homeobox family. Comparative promoter and homeodomain sequence analyses suggest that it is related to the Hox11 gene, which belongs to the Tlx homeobox family. Hox11 is highly expressed in proliferating progenitor cells, but expression is downregulated during cell differentiation. Using reporter gene methodology, we monitored function of the sponge EmH-3 promoter transfected into human erythroleukemia K562 cells. These cells express the Tlx/Hox11 gene constitutively, and downregulate its expression upon differentiation. The same pattern of expression and downregulation was observed for the sponge reporter construct. We propose that Tlx/Hox11 genes have structural and functional homologies conserved in phylogenetically distant groups, that represent a deep homology in the regulation of cell proliferation, commitment and differentiation.
Coutinho
Cristiano C
CC
Laboratory of Molecular Biology of Embryonic Development, Federal University of Rio de Janeiro, 21941-970 Ilha do Fundão, Rio de Janeiro, Brazil. ccoutinho@hotmail.com
Fonseca
Rodrigo N
RN
Mansure
José João C
JJ
Borojevic
Radovan
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D019070:Cell Lineage; D015536:Down-Regulation; D017930:Genes, Reporter; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics*; D006801:Humans; D020014:K562 Cells; D051741:Kruppel-Like Transcription Factors; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism; D015513:Oncogene Proteins / Q000235:genetics*; D010802:Phylogeny; D011161:Porifera; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000378:metabolism
C116345:EmH-3 protein, Ephydatia muelleri; C430270:Gli5 protein, mouse; D018398:Homeodomain Proteins; D051741:Kruppel-Like Transcription Factors; D009419:Nerve Tissue Proteins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; C487378:Tlx1 protein, mouse; D014157:Transcription Factors; C071250:TLX1 protein, human; D008156:Luciferases