3D Atlas of the Pituitary Gland of the Model Fish Medaka (Oryzias latipes)

Abstract

In vertebrates, the anterior pituitary plays a crucial role in regulating several essential physiological processes via the secretion of at least seven peptide hormones by different endocrine cell types. Comparative and comprehensive knowledge of the spatial distribution of those endocrine cell types is required to better understand their physiological functions. Using medaka as a model and several combinations of multi-color fluorescence in situ hybridization, we present the first 3D atlas revealing the gland-wide distribution of seven endocrine cell populations: lactotropes, thyrotropes, Lh and Fsh gonadotropes, somatotropes, and pomca-expressing cells (corticotropes and melanotropes) in the anterior pituitary of a teleost fish. By combining in situ hybridization and immunofluorescence techniques, we deciphered the location of corticotropes and melanotropes within the pomca-expressing cell population. The 3D localization approach reveals sexual dimorphism of tshba-, pomca-, and lhb-expressing cells in the adult medaka pituitary. Finally, we show the existence of bi-hormonal cells co-expressing lhb-fshb, fshb-tshba and lhb-sl using single-cell transcriptomics analysis and in situ hybridization. This study offers a solid basis for future comparative studies of the teleost pituitary and its functional plasticity.

Pituitary Gonadotropin Gene Expression During Induced Onset of Postsmolt Maturation in Male Atlantic Salmon: In Vivo and Tissue Culture Studies

“…Our data on the KEGG pathway enrichment analysis also indicated that, similar to zebrafish ( 67 ) and medaka ( 64 ), genes related to cell adhesion and extracellular matrix (ECM) are modulated in the pituitary during the start of puberty. This is in accordance with previous studies in mammals, in which components of the ECM were shown to modulate pituitary cell proliferation and hormone secretion ( 110 ).…”

“…In both zebrafish ( 67 ) and medaka ( 64 ), but not in salmon (this RNAseq study analyzing samples collected within 1.5 weeks after starting the exposure to stimulatory conditions), lhb expression levels were also increased after the start of puberty. This discrepancy probably reflects the fact that those studies compared juvenile −immature− with adult −mature− stages while here, we compare two early stages of development, representing fish before and about to enter puberty, but prior to histologically visible signs of testis maturation.…”

“…Studies using transgenic zebrafish and tilapia ( Oreochromis niloticus ) expressing fluorescence-tagged gonadotropes ( 62 ) and single-cell RNAseq of tilapia pituitaries ( 63 ) confirmed that Fsh and Lh are synthesized and secreted from distinct cells. However, a study in medaka that combined multi-color in situ hybridization (ISH) and single-cell RNAseq analyses revealed the existence of a small fraction (4%) among the gonadotrophs co-expressing fshb and lhb ( 64 ). Furthermore, in primary cell culture, medaka Fsh cells can produce Lhb ( 65 ).…”

“…However, knowledge on genes/pathways operating in the teleost pituitary during the initiation of puberty and their potential involvement in the regulation of gonadotropin production and release is still limited. A few studies have examined global changes on pituitary gene expression, comparing juvenile and adult males in model fish species ( 64 , 67 ). However, no information is available on transcriptional changes in the pituitary during the narrow time window of initiating male puberty.…”

Sperm collection and computer-assisted sperm analysis in the teleost model Japanese medaka (Oryzias latipes)

“…Unlike zebrafish, medaka have a sex-determining gene (Matsuda et al, 2002), and a high temperature (from 4–40 °C) and salinity (euryhaline species) tolerance (Sakamoto et al, 2001). Also, many genetic and anatomical tools, as well as protocols (Ager-Wick et al, 2018; Fontaine et al, 2018; Fontaine & Weltzien, 2019; Murata et al, 2019; Porazinski et al, 2010; Royan et al, 2020, 2021), have been developed in medaka to facilitate the study of its biology.…”