Biology subjects

Tomihara, S.

Publications and source records attributed to Tomihara, S..

3 recordsLinked to original sources

bioRxiv2026

The mitochondrial genome of the hammerhead flatworm Bipalium nobile and its phylogenetic implications

We sequenced the nearly complete mitochondrial genome of the hammerhead flatworm Bipalium nobile Kawakatsu and Makino, 1982 using short-read sequencing technology, yielding a 16,018 bp genome comprising 12 protein-coding genes, 22 tRNA genes, and 2 rRNA genes. The composition and order of genes were consistent with those observed in the closely related species Bipalium kewense and Diversibipalium multilineatum, except for the position of tRNA-Glu. Phylogenetic analysis based on all mitochondrial proteins from species within the family Geoplanidae supports the monophyly of a clade comprising B. nobile, B. kewense, and D. multilineatum. The mitochondrial genome sequence obtained in this study provides a valuable resource for investigating the genetic diversity and population structure of B. nobile, a soil-dwelling predator with the potential for global spread as an invasive organism.

zoology↗

bioRxiv2024

Sexual receptivity increases in synchrony with the ovulatory cycle in female medaka

Successful reproduction requires coordinated regulation of gonadal function and sexual behavior. However, the mechanisms of such a regulation remain elusive. Here, we used a teleost medaka to find out possible involvement of ovulation in the control of female sexual behaviors by analyzing the sexual behaviors of the female gene-knockout medaka that do not ovulate and found that ovulation is essential for the facilitation of female sexual receptivity. Behavioral recordings and anatomical examinations showed that the sexual behavior of medaka occurs only after the ovulation. Furthermore, progesterone administration partially reinstated the sexual receptivity of the anovulatory knockout females. Taken together with the result that progesterone receptor is expressed in the brain regions that are considered strong candidate for regulation of sexual behavior, we propose that female sexual receptivity is facilitated in synchrony with the ovulatory cycle via progesterone receptor signaling in specific brain regions that occurs around the timing of ovulation.

physiology↗

bioRxiv2023

Enhancer evolution as a driving force for lineage-specific paralog usage in the central nervous system.

Expression patterns of paralogous genes in the functionally homologous cells sometimes show differences across species. However, no reasonable explanation for the mechanism underlying such phenomena has been discovered. To understand this mechanism, the present study focused on the hypophysiotropic GnRH neurons in vertebrates as a model. These neurons express either gnrh1 or gnrh3 paralogs depending on species, and apparent switching of the expressed paralogs in them occurred at least four times in vertebrate evolution. First, we found redundant expressions of gnrh1 and gnrh3 in a single neuron in piranha and hypothesized that this situation may indicate an ancestral condition. We tested this hypothesis by examining the activity of piranha gnrh1/gnrh3 enhancers in zebrafish and medaka, in which the two gnrh paralogs are not co-expressed. Here, the gnrh1/gnrh3 enhancer of piranha induced reporter RFP/GFP co-expressions in a single hypophysiotropic GnRH neuron in both zebrafish and medaka. From these results, we propose that long-lasting ([~]550 My) redundancy after gnrh1/3 duplication in 1R/2R WGD may be the key to apparent switching of the paralog usage among the present-day species. Moreover, interspecies analyses of enhancers indicated that the loss of enhancers rather than changes in trans-regulatory elements drove the role-division of these paralogs.

evolutionary biology↗