Development of the adenohypophysis in the lamprey: evolution of epigenetic patterning programs in organogenesis.
In gnathostomes, the adenohypophysis, a component of the hypothalamo-hypophysial complex, is believed to develop through hierarchically organized epigenetic interactions based primarily on the topographical relationships between tissues. From a comparison of developmental processes and gene expression patterns of pituitary-related genes between the agnathan species, lampreys and gnathostomes, we speculate on the evolutionary pathway of the vertebrate adenohypophysis. In the lamprey, this is derived from the nasohypophysial placode (NHP) that develops anterior to the oral ectoderm. The NHP can be identified by the expression of LjPitxA, before actual histogenesis, but it is initially distant from the future hypothalamic region. Subsequently, the NHP expresses both LjFgf8/17 and LjBmp2/4a gene transcripts, and grows caudally to establish a de novo contact with the hypothalamic region by the mid-pharyngula stage. Later, the NHP gives rise to both the adenohypophysis and an unpaired nasal organ. Thus, the topographical relationship between the NHP and the hypothalamic region is established secondarily in the lamprey, unlike gnathostomes in which the equivalent relationship appears early in development. Comparing the developmental pattern of the amphioxus homologue of the adenohypophysis, we hypothesize that a modification of the regulation of the growth factor encoding gene lies behind the evolutionary changes recognized as heterochrony and heterotopy, which leads to the gnathostome hypophysial developmental pattern.
Laboratory for Evolutionary Morphology, Center for Developmental Biology, RIKEN, Kobe, Hyogo 650-0047, Japan. k-uchida@cdb.riken.go.jp
Katsuhisa
K
Uchida
Yasunori
Y
Murakami
Shigehiro
S
Kuraku
Shigeki
S
Hirano
Shigeru
S
Kuratani
D000818:Animals; D001483:Base Sequence; D016000:Cluster Analysis; D017931:DNA Primers; D004475:Ectoderm; D044127:Epigenesis, Genetic / Q000235:genetics; D015870:Gene Expression; D053823:Hedgehog Proteins; D006652:Histological Techniques; D018398:Homeodomain Proteins / Q000235:genetics; D017403:In Situ Hybridization; D007564:Japan; D007798:Lampreys / Q000033:anatomy & histology / Q000196:embryology* / Q000235:genetics*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D038081:Organogenesis / Q000235:genetics; D010802:Phylogeny; D010903:Pituitary Gland, Anterior / Q000033:anatomy & histology / Q000196:embryology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D000097577:Homeobox Protein PITX2
D017931:DNA Primers; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2