Evolution of the AZFc Region in Primates


The Azoospermia Factor c (AZFc) region on the human Y chromosome is one of the most polymorphic regions in the human genome. It encodes several gene families with germ‐cell specific expression and is frequently deleted in infertile men with very low sperm counts or no sperm. AZFc consists mainly of very long repeats (amplicons) that have different evolutionary histories. Some of the ampliconic sequences are remnants of the ancient Y chromosome and share homology with the X chromosome. Other sequences arrived on the Y chromosome through segmental duplication and transposition of autosomal sequences or through messenger ribonucleic acid (mRNA) retroposition. Subsequent rearrangements such as duplication, inversion and intragenic amplification result in the various structures found on the Y chromosomes of today's primates.

Key Concepts

  • The AZFc region on the human Y chromosome contains several testis‐specific gene families and is essential for normal spermatogenesis.

  • The AZFc region consists mainly of large amplicons and is prone to rearrangement such as deletion, duplication and inversion.

  • Some ampliconic sequences are remnants of the ancestral Y chromosome and retain sequence similarity with the X chromosome.

  • Other AZFc sequences arrived on the Y chromosome at various time during primate evolution through duplication and transposition of autosomal sequences.

  • The CDY gene within the yellow amplicon arose from retroposition of an ancient autosomal CDYL gene and contains no introns.

Keywords: Y chromosome; AZFc; segmental duplication; primate evolution

Figure 1.

The AZFc region on the human Y chromosome. (a) The locations of the AZF regions on the Y chromosome. (b) The prototype architecture of AZFc. The amplicons are color‐coded according to Kuroda‐Kawaguchi et al.. The three palindromes (P1, P2 and P3) are indicated. The gene families are shown, as well as regions homologous to autosomes, with the autosome numbers indicated below or next the bars. Three common deletions of the region are shown at the bottom.

Figure 2.

The DAZ protein family. Arrows represent the RNA recognition motifs and triangles represent the DAZ repeats. Different DAZ repeat units are indicated with different color. The C‐termini of the proteins, depicted as rectangles, lack significant similarity.

Figure 3.

Evolution of the AZFc amplicons on the primate Y chromosomes. The blue and the light‐blue amplicons as well as the distal portion of the yellow amplicons represent the remnants of the ancient Y chromosome. The red dot within the yellow amplicon depicts the retroposion CDY which arrived on the Y chromosome during early mammalian evolution. The other amplicons arrived at different time during primate evolution. The amplification and rearrangement of the red amplicon after its arrival on the Y chromosome have been studied and are indicated. The copy number and the arrangement of other amplicons in the nonhuman primates remain unknown.



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Yu, Yueh‐Hsiang, and Yen, Pauline H(Sep 2009) Evolution of the AZFc Region in Primates. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021967]