The evolutionary emergence of cell type-specific genes inferred from the gene expression analysis of Hydra.
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.
Hwang
Jung Shan
JS
Center for Information Biology and DNA Data Bank of Japan, National Institute of Genetics, Mishima, Shizuoka 411-8540 Japan.
Ohyanagi
Hajime
H
Hayakawa
Shiho
S
Osato
Naoki
N
Nishimiya-Fujisawa
Chiemi
C
Ikeo
Kazuho
K
David
Charles N
CN
Fujisawa
Toshitaka
T
Gojobori
Takashi
T
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
D018076:DNA, Complementary