# Sexually dimorphic dynamics of the microtubule network in medaka (Oryzias latipes) germ cells

## TL;DR

This study identifies a microtubule structure in medaka fish germ cells that contributes to oocyte polarity and is maintained in females but not in males.

## Contribution

The study reveals a sex-specific microtubule structure in medaka germ cells that is crucial for oocyte polarity and influenced by genetic pathways.

## Key findings

- A dome-shaped microtubule structure is established in primordial germ cells and maintained during oogenesis.
- The microtubule dome is destabilized in spermatogonia influenced by Sertoli cells expressing dmrt1.
- Disruption of the microtubule dome leads to dispersal of bucky ball RNA, suggesting a role in the Balbiani body.

## Abstract

Gametogenesis is the process through which germ cells differentiate into sexually dimorphic gametes, eggs and sperm. In the teleost fish medaka (Oryzias latipes), a germ cell-intrinsic sex determinant, foxl3, triggers germline feminization by activating two genetic pathways that regulate folliculogenesis and meiosis. Here, we identified a pathway involving a dome-shaped microtubule structure that may be the basis of oocyte polarity. This structure was first established in primordial germ cells in both sexes, but was maintained only during oogenesis and was destabilized in differentiating spermatogonia under the influence of Sertoli cells expressing dmrt1. Although foxl3 was dispensable for this pathway, dazl was involved in the persistence of the microtubule dome at the time of gonocyte development. In addition, disruption of the microtubule dome caused dispersal of bucky ball RNA, suggesting the structure may be prerequisite for the Balbiani body. Collectively, the present findings provide mechanistic insight into the establishment of sex-specific polarity through the formation of a microtubule structure in germ cells, as well as clarifying the genetic pathways implementing oocyte-specific characteristics.

Summary: A dome-shaped microtubule structure is identified in medaka that is present prior to sex determination in primordial germ cells and is maintained in females, contributing to oocyte polarity.