A homozygous TRIP13 pathogenic variant associated with familiar oocyte arrest and prematurely condensed sperm chromosomes

Abstract

We report on a consanguineous family with two infertile sisters with oocyte arrest and prematurely condensed sperm chromosomes. A genome-wide linkage scan and exome sequencing revealed a homozygous variant in the gene for the thyroid receptor interacting protein 13 (TRIP13), c.518G˃A (p.Arg173Gln), affecting an evolutionary highly conserved amino acid within an ATP binding motif. Just recently, compound heterozygosity for this variant was described in a Chinese proband as pathogenic, confirming that the homozygous mutation is causative for the oocyte arrest. The TRIP13 gene and the orthologous yeast pch2 gene are, amongst others, involved in a meiotic checkpoint control. This checkpoint defect is obviously responsible for the premature condensation of the sperm chromosomes. TRIP13 and pch2 are involved in meiotic recombination. To exclude that it is involved in reciprocal somatic exchanges, we analyzed the rate of sister chromatid exchanges (SCEs) in the proband´s lymphoblastoid cells. Obviously, TRIP13 is not involved in this type of somatic recombination. Moreover, we tested whether TRIP13 can complement the defect of the yeast pch2 gene. Using a yeast deletion strain lacking pch2, we integrated plasmids containing either the yeast pch2 or the human TRIP13 gene, both harboring the wild-type or the mutant allele and assessed the crossingover rate between marker genes lys2 and leu2 as a measure of complementation. Evidence is presented that the human plasmids, unexpectedly also that with the mutation, could complement the pch2 deficient yeast strain, underlining that the evolutionary conservation at the molecular level obviously extends to the functional level.

Keywords: Complementation study; Human TRIP13; Oocyte arrest; Premature chromosome condensation; Sister chromatid exchanges; Yeast pch2.

Fig. 1

Pedigree of a consanguineous family (parents are first cousins) with two sisters with oocyte arrest (black circles), two sisters (II.5, II.6) with two and four children each and two childless married brothers (grey boxes). The oocytes of II.1 and II.2 were arrested at MI and showed prematurely condensed sperm chromosomes [45]. The affected sisters are homozygous (A/A) for the TRIP13 missense variant (c.518G˃A) resulting in the replacement of arginine by glutamine (p.Arg173Gln). One sister (II.6) is homozygous for the wild type allele (G/G). The missense variant maps to the large AAA + ATPase domain (Ye et al. 2017)

Fig. 2

Distribution of the number of sister chromatid exchanges/cell in lymphoblastoid cells of five family members (II.1 and II.2 with oocyte arrest) and a control. The difference to the control was calculated with the Mann–Whitney U-Test, two-tailed. Inset: Metaphase of II.1 with high SCE rate

Fig. 3

Evolutionary conservation in orthologues of selected species of the amino acid sequence flanking arginine (R) at position 173 of the human TRIP13 gene. The yeast (Pch2) amino acid sequence is based on the Needleman-Wunsch alignment (Altschul 1997) with the human TRIP13 protein

Fig. 4

Confirmation of successful transformation of the yeast deletion strain Y33326 with the various plasmids (A) or the leu2 cassette (B). Total DNA was extracted from the various strains, the plasmids (with the genes) amplified, the PCR products separated on agarose gels and identified by UV light. The length of the bands (M) is given in kb. Wt: wild type strain Y20000 with the pch2 gene and the empty p416GPD vector. pch2Δ: deletion strain Y33326 without the pch2 gene, with the TRIP13 wild type gene (T13wt) or its mutant allele c.518G˃A (T13m), with the pch2 gene (pch2) and the pch2 gene plus intron (pch2i). Y20: wild type strain Y20000; Y33 deletion strain Y33326