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. 2012:2012:430587.
doi: 10.1155/2012/430587. Epub 2011 Dec 22.

Homologue pairing in flies and mammals: gene regulation when two are involved

Manasi S Apte  1 , Victoria H Meller
Affiliations

Homologue pairing in flies and mammals: gene regulation when two are involved

Manasi S Apte et al. Genet Res Int. 2012.

Abstract

Chromosome pairing is usually discussed in the context of meiosis. Association of homologues in germ cells enables chromosome segregation and is necessary for fertility. A few organisms, such as flies, also pair their entire genomes in somatic cells. Most others, including mammals, display little homologue pairing outside of the germline. Experimental evidence from both flies and mammals suggests that communication between homologues contributes to normal genome regulation. This paper will contrast the role of pairing in transmitting information between homologues in flies and mammals. In mammals, somatic homologue pairing is tightly regulated, occurring at specific loci and in a developmentally regulated fashion. Inappropriate pairing, or loss of normal pairing, is associated with gene misregulation in some disease states. While homologue pairing in flies is capable of influencing gene expression, the significance of this for normal expression remains unknown. The sex chromosomes pose a particularly interesting situation, as females are able to pair X chromosomes, but males cannot. The contribution of homologue pairing to the biology of the X chromosome will also be discussed.

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Figures

Figure 1
Figure 1
Modes of somatic pairing in mammalian tissues. (a) Pericentromeric homologue pairing in parts of the brain. Centromeres are depicted by black dots. (b) Abnormal pairing of chromosome 19q in renal carcinoma. (c) Looping between two sites on a chromosome (left) and interchromosomal contacts (right) are mediated by sequence-specific DNA-binding proteins such as CTCF (triangle) and cohesin (brown circle). (d) Pairing of the X inactivation center (Xic) initiates X chromosome inactivation in females. Sequences that participate in Xic pairing are depicted. The X-pairing region (Xpr, yellow) initiates Xic pairing. Tsix (light blue) and Xite (pink) pair transiently, enabling counting and choice to occur. Oct4 and CTCF are necessary for contact and communication at the Xic. Oct4-binding sites (green ovals) and CTCF-binding sites (triangles) within the Tsix and Xite regions of the mouse Xic are depicted.
Figure 2
Figure 2
Hypothetical model for pairing-dependent buffering of gene dosage in flies. (a) The unpaired X chromosome of males escapes repression. (b) Paired female X chromosomes are subject to repression. (c) Paired regions of an autosome are repressed, but an unpaired region created by deficiency escapes repression.
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