title: The evolutionary emergence of cell type-specific genes inferred from the gene expression analysis of Hydra.
abstract: Cell lineages of cnidarians including Hydra represent the fundamental cell types of metazoans and provides us a unique opportunity to study the evolutionary diversification of cell type in the animal kingdom. Hydra contains epithelial cells as well as a multipotent interstitial cell (I-cell) that gives rise to nematocytes, nerve cells, gland cells, and germ-line cells. We used cDNA microarrays to identify cell type-specific genes by comparing gene expression in normal Hydra with animals lacking the I-cell lineage, so-called epithelial Hydra. We then performed in situ hybridization to localize expression to specific cell types. Eighty-six genes were shown to be expressed in specific cell types of the I-cell lineage. An additional 29 genes were expressed in epithelial cells and were down-regulated in epithelial animals lacking I-cells. Based on the above information, we constructed a database (http://hydra.lab.nig.ac.jp/hydra/), which describes the expression patterns of cell type-specific genes in Hydra. Most genes expressed specifically in either I-cells or epithelial cells have homologues in higher metazoans. By comparison, most nematocyte-specific genes and approximately half of the gland cell- and nerve cell-specific genes are unique to the cnidarian lineage. Because nematocytes, gland cells, and nerve cells appeared along with the emergence of cnidarians, this suggests that lineage-specific genes arose in cnidarians in conjunction with the evolution of new cell types required by the cnidarians.
authors.affiliation: Center for Information Biology and DNA Data Bank of Japan, National Institute of Genetics, Mishima, Shizuoka 411-8540 Japan.
authors.forename: Jung Shan
authors.initials: JS
authors.lastname: Hwang
authors.forename: Hajime
authors.initials: H
authors.lastname: Ohyanagi
authors.forename: Shiho
authors.initials: S
authors.lastname: Hayakawa
authors.forename: Naoki
authors.initials: N
authors.lastname: Osato
authors.forename: Chiemi
authors.initials: C
authors.lastname: Nishimiya-Fujisawa
authors.forename: Kazuho
authors.initials: K
authors.lastname: Ikeo
authors.forename: Charles N
authors.initials: CN
authors.lastname: David
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Fujisawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Gojobori
mesh_terms: D000818:Animals; D019070:Cell Lineage; D018076:DNA, Complementary; D016208:Databases, Factual; D019143:Evolution, Molecular; D015870:Gene Expression; D006829:Hydra / Q000166:cytology* / Q000235:genetics*; D017403:In Situ Hybridization; D020411:Oligonucleotide Array Sequence Analysis
chemical_list: D018076:DNA, Complementary