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A human infertility-associated KASH5 variant promotes mitochondrial localization.

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A KASH5 gene variant linked to male infertility causes the KASH5 protein to mislocalize from the nuclear envelope to mitochondria. This mistargeting disrupts its function in chromosome pairing, explaining azoospermia.

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Area of Science:

  • Cell Biology
  • Genetics
  • Reproductive Biology

Background:

  • KASH5 is a protein of the outer nuclear membrane (ONM) and endoplasmic reticulum (ER) essential for homologous chromosome pairing during meiosis.
  • A KASH5 variant (L535Q) has been associated with male infertility and azoospermia, but the underlying molecular mechanism remains unclear.

Purpose of the Study:

  • To elucidate the molecular mechanism by which the L535Q KASH5 variant leads to male infertility and azoospermia.
  • To investigate the impact of the L535Q substitution on KASH5 protein localization and function.

Main Methods:

  • Analysis of the L535Q substitution within the KASH5 transmembrane domain (TMD) using hydrophobicity scales (GES).
  • Amino acid substitution studies to assess the effects on KASH5 subcellular localization.
  • Investigated localization to the ER, ONM, and mitochondrial membranes.

Main Results:

  • The L535Q substitution reduces the hydrophobicity of the KASH5 TMD.
  • This change in hydrophobicity causes KASH5 to mislocalize from the ER and ONM to the mitochondrial membrane.
  • The L535Q substitution perturbs normal KASH5 localization.

Conclusions:

  • The L535Q KASH5 variant's mislocalization to mitochondria disrupts its function in nuclear envelope-chromosome interactions.
  • This mistargeting provides a molecular explanation for the observed male infertility and azoospermia phenotype in patients carrying the L535Q variant.