Two missense STK11 gene variations impaired LKB1/adenosine monophosphate-activated protein kinase signaling in Peutz-Jeghers syndrome

BACKGROUND

Peutz-Jeghers syndrome (PJS) is a rare hereditary neoplastic disorder mainly associated with serine/threonine kinase 11 (STK11/LKB1) gene mutations. Preimplantation genetic testing can protect a patient's offspring from mutated genes; however, some variations in this gene have been interpreted as variants of uncertain significance (VUS), which complicate reproductive decision-making in genetic counseling.

AIM

To identify the pathogenicity of two missense variants and provide clinical guidance.

METHODS

Whole exome gene sequencing and Sanger sequencing were performed on the peripheral blood of patients with PJS treated at the Reproductive and Genetic Hospital of Citic-Xiangya. Software was employed to predict the protein structure, conservation, and pathogenicity of the two missense variation sites in patients with PJS. Additionally, plasmids were constructed and transfected into HeLa cells to observe cell growth. The differences in signal pathway expression between the variant group and the wild-type group were compared using western blot and immunohistochemistry. Statistical analysis was performed using one-way analysis of variance. P < 0.05 was considered statistically significant.

RESULTS

We identified two missense STK11 gene VUS [c.889A>G (p.Arg297Gly) and c.733C>T (p.Leu245Phe)] in 9 unrelated PJS families who were seeking reproductive assistance. The two missense VUS were located in the catalytic domain of serine/threonine kinase, which is a key structure of the liver kinase B1 (LKB1) protein. In vitro experiments showed that the phosphorylation levels of adenosine monophosphate-activated protein kinase (AMPK) at Thr172 and LKB1 at Ser428 were significantly higher in transfected variation-type cells than in wild-type cells. In addition, the two missense STK11 variants promoted the proliferation of HeLa cells. Subsequent immunohistochemical analysis showed that phosphorylated-AMPK (Thr172) expression was significantly lower in gastric, colonic, and uterine polyps from PJS patients with missense variations than in non-PJS patients. Our findings indicate that these two missense STK11 variants are likely pathogenic and inactivate the STK11 gene, causing it to lose its function of regulating downstream phosphorylated-AMPK (Thr172), which may lead to the development of PJS. The identification of the pathogenic mutations in these two clinically characterized PJS patients has been helpful in guiding them toward the most appropriate mode of pregnancy assistance.

CONCLUSION

These two missense variants can be interpreted as likely pathogenic variants that mediated the onset of PJS in the two patients. These findings not only offer insights for clinical decision-making, but also serve as a foundation for further research and reanalysis of missense VUS in rare diseases.

Defects in phospholipase C zeta cause polyspermy and low fertilization after conventional IVF: not just ICSI failure

ABSTRACT

Phospholipase C zeta (PLCζ) is a key sperm-borne oocyte-activating factor that triggers Ca2+ oscillations and the subsequent block to polyspermy following gamete fusion. Mutations in PLCZ1, the gene encoding PLCζ, cause male infertility and intracytoplasmic sperm injection (ICSI) fertilization failure; and PLCζ expression and localization patterns are significantly correlated with ICSI fertilization rate (FR). However, in conventional in vitro fertilization (cIVF), whether and how sperm PLCζ affects fertilization remain unclear. Herein, we identified one previously reported and two novel PLCZ1 mutations associated with polyspermy in vitro that are characterized by excessive sperm-zona binding and a delay in pronuclei (PN) formation. Immunofluorescence staining and oocyte activation testing revealed that virtually all spermatozoa from patients lacked functional PLCζ and were thus unable to evoke Ca2+ oscillations. ICSI with an artificial oocyte activation treatment successfully rescued the polyspermic phenotype and resulted in a live birth. Furthermore, we analyzed PLCζ in an additional 58 males after cIVF treatment in the Reproductive and Genetic Hospital of CITIC-Xiangya (Changsha, China) between February 2019 and January 2022. We found that the proportion of spermatozoa that expressed PLCζ was positively correlated with both 2PN rate and total FR. The optimal cutoff value below which males were likely to experience low FR (total FR ≤30%) after cIVF was 56.7% for the proportion of spermatozoa expressing PLCζ. Our study expands the mutation and the phenotypic spectrum of PLCZ1 and further suggests that PLCζ constitutes a promising biomarker for identifying low FRs cases in cIVF due to sperm-related oocyte activation deficiency and that sperm PLCζ analysis may benefit the wider male population and not only men with ICSI failure.

RNA splicing analysis contributes to reclassifying variants of uncertain significance and improves the diagnosis of monogenic disorders

BACKGROUND

Numerous variants of uncertain significance (VUSs) have been identified by whole exome sequencing in clinical practice. However, VUSs are not currently considered medically actionable.

OBJECTIVE

To assess the splicing patterns of 49 VUSs in 48 families identified clinically to improve genetic counselling and family planning.

METHODS

Forty-nine participants with 49 VUSs were recruited from the Reproductive and Genetic Hospital of CITIC-Xiangya. Bioinformatic analysis was performed to preliminarily predict the splicing effects of these VUSs. RT-PCR and minigene analysis were used to assess the splicing patterns of the VUSs. According to the results obtained, couples opted for different methods of reproductive interventions to conceive a child, including prenatal diagnosis and preimplantation genetic testing (PGT).

RESULTS

Eleven variants were found to alter pre-mRNA splicing and one variant caused nonsense-mediated mRNA decay, which resulted in the reclassification of these VUSs as likely pathogenic. One couple chose to undergo in vitro fertilisation with PGT treatment; a healthy embryo was transferred and the pregnancy is ongoing. Three couples opted for natural pregnancy with prenatal diagnosis. One couple terminated the pregnancy because the fetus was affected by short-rib thoracic dysplasia and harboured the related variant. The infants of the other two couples were born and were healthy at their last recorded follow-up.

CONCLUSION

RNA splicing analysis is an important method to assess the impact of sequence variants on splicing in clinical practice and can contribute to the reclassification of a significant proportion of VUSs. RNA splicing analysis should be considered for genetic disease diagnostics.

Evidence of balancing selection in multiple indigenous chicken populations

Microsatellite DNA markers, which are assumed to drift, have been widely used to assess genetic diversity in all major domestic animal species. These markers provide insight into the arrival and dispersion history of a species, with regard to their content or management history. However, no direct evidence supports current standard microsatellite markers falling under this assumption. Therefore, the objective of this study was to investigate the effect and divergence of microsatellites under different types of selection on genetic patterns and population diversity. A total of 192 birds (Gallus gallus) from eight different geographic locations were investigated using 20 microsatellites that are classified into different groups by their selective effect (neutral, positive selection, and balancing selection) by the FDIST2 outlier test. The results showed that most polymorphisms were in the balancing selection marker group, the expected heterozygosity was 0.70, the observed heterozygosity was 0.65, and the mean number of alleles was 6.91. AMOVA revealed that the balancing group contributed the lowest amount of variance among groups, which was -0.60%, the highest variance contributed within the population being 92.28% in comparison with that of other groups. A similar pattern of population genetics was revealed following Slatkin linearized FST, principal component factor analysis, and population structure by Bayesian clustering. In conclusion, balancing selective markers offer high polymorphism for estimating genetic diversity but reduced genetic divergence between populations.

Trace levels of mitomycin C disrupt genomic integrity and lead to DNA damage response defect in long-term-cultured human embryonic stem cells

How to maintain the genetic integrity of cultured human embryonic stem (hES) cells is raising crucial concerns for future clinical use in regenerative medicine. Mitomycin C(MMC), a DNA damage agent, is widely used for preparation of feeder cells in many laboratories. However, to what extent MMC affects the karyotypic stability of hES cells is not clear. Here, we measured residual MMC using High Performance Liquid Chromatography-Mass Spectrometry/Mass Spectrometry following each step of feeder preparation and found that 2.26 ± 0.77 and 3.50 ± 0.92 ng/ml remained in mouse feeder cells and human feeder cells, respectively. In addition, different amounts of MMC caused different chromosomal aberrations in hES cells. In particular, one abnormality, dup(1)(p32p36), was the same identical to one we previously reported in another hES cell line. Using Affymetrix SNP 6.0 arrays, the copy number variation changes of the hES cells maintained on MMC-inactivated feeders (MMC-feeder) were significantly more than those cultured on γ-inactivated feeder (IR-feeder) cells. Furthermore, DNA damage response (DDR) genes were down-regulated during long-term culture in the MMC-containing system, leading to DDR defect and shortened telomeres of hES cells, a sign of genomic instability. Therefore, MMC-feeder and MMC-induced genomic variation present an important safety problem that would limit such hES from being applied for future clinic use and drug screening.