Abstract
Meiotic DNA double-strand breaks produce reciprocally exchanged DNA strands, which mature into chiasmata that hold homologous chromosomes together as bivalents. These bivalents are subsequently separated in the first meiotic division. In a mutant lacking the newly identified Tetrahymena gene APRO1 (Anaphase promoting 1), meiosis is arrested by the end of prophase. Mature chiasmata are not formed but bivalents are connected via a molecular precursor structure. In-depth analysis of this arrested intermediate structure may help to elucidate the noncanonical molecular recombination pathway in Tetrahymena.
Highlights
IntroductionMeiotic crossovers form the basis of genetic recombination, which contributes to diversity in sexual progeny through generating novel combinations of traits
We report a gene, APRO1 (Anaphase promoting 1), in whose absence meiosis is arrested by the end of prophase, with incomplete crossovers and bivalents adopting an unusual tandem arrangement
APRO1 had been knocked out because its expression in early conjugating (= meiotic) cells suggested a function in meiosis or the post-meiotic stages of sexual reproduction [5]. (For the expression profile of TTHERM_00112830 (APRO1) see http://tfgd.ihb.ac.cn/ [16]
Summary
Meiotic crossovers form the basis of genetic recombination, which contributes to diversity in sexual progeny through generating novel combinations of traits. These can become fixed in species via natural selection. Crossovers are initiated by programmed DNA double-strand breaks (DSBs; see [1]). The 5 ́ strands of DNA ends flanking DSBs become resected and 3 ́ single-stranded DNA tracts invade double-stranded DNA molecules. Stand invasion enables the search for complementary base sequences, i.e. homologous chromosome regions. At these sites, the invading strand can initiate reciprocal recombination by crosswise ligation with the corresponding strand from the homolog. Chiasmata connect pairs of homologous chromosomes ( called a bivalent) until the first meiotic division, when the diploid somatic chromosome complement is reduced to a single gametic chromosome set
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