National Institute for Basic Biology

Division of Speciation Mechanisms II

Ken-ichirou Morohashi
Associate Professor:
Mitsuyasu Hasebe
Reserch Associate:
Graduate Students:
Technical Staff:

This division was newly established in 1996 with two research groups. These two groups managed by the professor, Ken-ichirou Morohashi (I), and the associate professor, Mitsuyasu Hasebe (II), have adopted animals and plants, respectively, as the materials for the research. Our attention has been and will be directed to understanding mechanisms underlying evolution of the reproductive system of animals and evolution of the morphology in plants. These efforts with a variety of the materials are expected to give us deeper insights into speciation mechanisms of organism.

I. Reproduction of animals

Because of the fundamental and pivotal function of the gonads, extensive efforts have been made to characterize the differentiation processes including sex-dependent differentiation. By focusing on the steroidogenesis as one of the gonad specific functions, we indentified a steroidogenic tissue specific transcription factor designated Ad4BP or SF-1. Recent studies with an antiserum to Ad4BP/SF-1 and a gene disrupted mice clearly demonstrated that the transcription factor is essential for differentiation of the steroidogenic tissues, the gonads and the adrenal cortex. Showing a good correlation with the observation above, a particular cell population identified as Ad4BP/SF-1 immunoreactive cells (AGP, adreno-genital primordium) was revealed to give rise to the gonads and adrenal cortex. These observations gave us many interesting issues as follows. What is the signal for the onset of the Ad4BP/SF-1 gene transcription in the particular cells comprising AGP? What is the mechanism underlying the separation of the AGP into the adrenal and gonadal primordia? How is the mechanism employed for sex differentiation of the gonads? Why dose such sex dependent differentiation not occur in the adrenal cortex? To address the issues, the nuclear factors, WT1, SRY, SOX9, and DAX1 as well as Ad4BP/SF-1, critically implicated in gonadal and adrenocortical differentiation will be investigated from the molecular and morphological aspects.

II. Morphological Evolution in plants

Morphological diversity among taxa is the most prominent characteristics in the biodiversity. Our group aims to explore genetical and molecular changes which caused renovative morphological changes during the course of plant evolution. We selected Arabidopsis (angiosperm), Gnetum (gymnosperm), Ginkgo (gymnosperm), Ceratopteris (pteridophyte), Physcomitrella (bryophyte), and Chlamydomonas (green algae) as model plants to compare the genes related to morphogenesis. We are focusing on the following three topics; (1) Evolution of floral homeotic genes (MADS gene family and LEAFY gene homeologue, which is a regulator of the MADS genes), (2) Comparison of homeobox gene functions between sporophyte and gametophyte generations to reveal the evolution of the both generations, and (3) establishment of mutant library of Physcomitrella patens to get new morphological mutants which have not been obtained from the study of the higher plants having only reduced gametophytic generations. Some MADS, LEAFY and homeobox genes have been cloned from the gymnosperms, Ceratopteris, Physcomitrella and the analyses of the expression pattern are in progress. Some of those genes were observed to be expressed in both gametophyte and sporophyte generations and the regulation systems are studied.
Last Modified: 12:00, June 27, 1997