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Doubly uniparental inheritance of mitochondria as a model system for studying germ line formation

Liliana Milani1, Fabrizio Ghiselli, Maria Gabriella Maurizii

  • 1Department of Biologia Evoluzionistica Sperimentale, University of Bologna, Bologna, Italy. liliana.milani@unibo.it

Plos One
|December 6, 2011
PubMed
Abstract

Insights

Doubly Uniparental Inheritance (DUI) allows both parents to transmit mitochondria. In male embryos, sperm mitochondria aggregate near the first cleavage furrow, contributing to male germ line formation.

Area of Science:

  • Mitochondrial genetics
  • Developmental biology
  • Bivalve reproduction

Background:

  • Doubly Uniparental Inheritance (DUI) contrasts with typical Strictly Maternal Inheritance (SMI) of mitochondria.
  • DUI involves inheritance of two mitochondrial genomes, one from eggs and one from sperm.
  • In bivalve molluscs with DUI, sperm mitochondria are selectively retained in male embryos.

Purpose of the Study:

  • To investigate the mechanism of sperm mitochondria distribution in male embryos of the DUI species Ruditapes philippinarum.
  • To understand how sperm mitochondria are localized to the germ line in DUI embryos.

Main Methods:

  • MitoTracker staining to visualize mitochondria.
  • Microtubule staining to examine spindle organization.
  • Transmission electron microscopy for ultrastructural analysis.
  • Immunocytochemical analysis for protein localization (Vasa).

Main Results:

  • Sperm mitochondria aggregate near the first cleavage furrow in male embryos.
  • The midbody of the first mitotic spindle aids in positioning sperm mitochondria.
  • The germ line determinant Vasa segregates to the same region as sperm mitochondria.
  • Sperm mitochondria are localized to the animal-vegetal axis, a region not involved in cleavage.

Conclusions:

  • Sperm mitochondria are directed to the germ line in DUI male embryos, co-localizing with germ plasm.
  • This specific localization suggests a role for sperm mitochondria in male germ line formation.
  • The mechanism may represent a variation of the mitochondrial bottleneck observed in other metazoans.
  • Egg factors likely recognize and actively transfer M-type sperm mitochondria into the germ line.

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