National Institute for Basic Biology

Evolutionary Biology and Biodiversity

LABORATORY OF BIOLOGICAL DIVERSITYOHNO Group
Assistant Professor:OHNO, Kaoru

The aim of this laboratory is to research reproductivehormones in invertebrates, especially in echinoderms, and toanalyze the mechanisms by which they work. The comparisons of such molecules and mechanisms in various species
are expected to provide insights into the evolution of reproductive hormone systems.

I. Gonadotropins in the starfish, Patiria pectinifera

Gonadotropins play important regulatory roles in reproduction in both vertebrates and invertebrates. The vertebrate
gonadotropins, LH and FSH, are structurally and functionallyconserved across various species, whereas no such moleculehas been identified in invertebrates. Some gonadotropic
hormones have been found in invertebrate species. An insulin-like peptide was reported to be responsible for the regulation of egg maturation in the mosquito, Aedes aegypti, thus
demonstrating the involvement of insulin signaling in egg
maturation among invertebrates.

The gonad-stimulating substance (GSS) of an echinoderm,the starfish, was the very first gonadotropin to be identified
in invertebrates. GSS mediates oocyte maturation in starfish
by acting on the ovary to produce the maturation-inducing
hormone (MIH), 1-methyladenine, which in turn induces thematuration of the oocytes. In this sense, GSS is functionallyidentical to vertebrate LH, especially piscine and amphibian
LHs, and acts on the ovarian follicle cells to produce MIH
to induce the final maturation or meiotic resumption of theoocyte. Considering the functional similarity that GSS shareswith vertebrate LH, it is very important from an evolutionary
point of view to know the chemical and molecular structure of GSS. We cloned the gene encoding the amino acidsequence of purified GSS from radial nerves of the starfish,
Pateria pectinifera. Interestingly, phylogenetic analyses
revealed that it belonged to the insulin/insulin-like growth
factor (IGF)/relaxin superfamily and, more precisely, to thesubclass of relaxin peptides (Figure 1).

II. S earch for reproductive hormones inechinoderms

In a collaborative effort with Prof. Yoshikuni and AssociateProf. Kurita’s Laboratory at Kyushu Univ., we are searching for reproductive hormones in echinoderms, including
starfishes, brittle stars, sea urchins, sea cucumbers, andcrinoids. The collaborating parties have been able to purify
physiological materials which induce egg maturation fromnerve extracts and analyze them with a protein sequencer anda tandem mass spectrometer in the analytical center of ourinstitute. One of them, named cubifrin, which is an NGIWYamide peptide, is in the sea cucumber Aposticopus japonicus.
We have identified many neuropeptides from our EST
analysis of nerve tissues and many from RNA-seq and WGS
data of the NCBI database. In particular, relaxin like peptide
precursor genes and insulin/IGF like peptide precursor genes
were identified from many species. We are producing theseneuropeptides in a chemical synthetic manner to provide tocollaborating researchers for biological assays.

III. S earch for the lost mutants of female
hormones E2 in Oryzias latipes

Sequence analysis by capillary sequencer was carried out
from the tilling library of O. latipes in order to analyze thefunction of fish female reproductive hormone E2 as a part ofour collaborative research. Upon the discovery of aromatasemutants, a detailed analysis was carried out using these strains.

Publication List:〔Original papers〕

Y., Miyazoe, D., Togawa, R., Yokoyama Keiko and Nakasone,• Nishiike,K., Miyata, M., Kikuchi, Y., Kamei, Y., Todo, T., Ishikawa-Fujiwara, T.,

Figure 1. Amino acid sequence of starfish GSS. (A) Comparison of theheterodimeric structure of starfish GSS with those of various representative members of the insulin superfamily. The cysteine bridges are shownin red. (B) Coding DNA sequence and predicted amino acid sequencesof GSS. Sequences of the A and B chains are shown in the green andblue boxes, respectively. Characters shown in red boldface indicate basic
dipeptides that are the sites of proteolytic cleavage. The inverted triangle
shows the deduced cleavage site of the signal peptide.

72•Ohno, K., Usami, T., Nagahama, Y., and Okubo, K. (2021). Estrogen
receptor 2b is the major determinant of sex-typical mating behavior
and sexual preference in medaka. Curr. Biol. 31, 1699-1710.e6. DOI:
10.1016/j.cub.2021.01.089
Yuhi, T., Nishimiya, O., Ohno, K., Takita, A., Inoguchi, T., Ura, K., and Takagi,Y. (2022). Cloning of cDNA encoding a newly recognized apolipoproteinlike protein and its expression in the northern sea urchin Mesocentrotus
nudus. Fish. Sci. 88, 259–273. DOI: 10.1007/s12562-022-01584-3