Core binding factor subunit β plays diverse and essential roles in the male germline

Much of the foundation for lifelong spermatogenesis is established prior to puberty, and disruptions during this developmental window negatively impact fertility long into adulthood. However, the factors that coordinate prepubertal germline development are incompletely understood. Here, we report that core-binding factor subunit-β (CBFβ) plays critical roles in prepubertal development and the onset of spermatogenesis. Using a mouse conditional knockout (cKO) approach, inactivation of Cbfb in the male germline resulted in rapid degeneration of the germline during the onset of spermatogenesis, impaired overall sperm production, and adult infertility. Utilizing a different Cre driver to generate another Cbfb cKO model, we determined that the function of CBFβ in the male germline is likely limited to undifferentiated spermatogonia despite expression in other germ cell types. Within undifferentiated spermatogonia, CBFβ regulates proliferation, survival, and overall maintenance of the undifferentiated spermatogonia population. Paradoxically, we discovered that CBFβ also distally regulates meiotic progression and spermatid formation but only with Cbfb cKO within undifferentiated spermatogonia. Spatial transcriptomics revealed that CBFβ modulates cell cycle checkpoint control genes associated with both proliferation and meiosis. Taken together, our findings demonstrate that core programs established within the prepubertal undifferentiated spermatogonia population are necessary for both germline maintenance and sperm production.

OR13. Cardiac Arrythmias on COVID19 Patients: Characteristics, Correlated Risk Factors and Associated Outcomes

Background

Arrythmias in COVID19 patients were often found. This study was aimed to investigate characteristic, risk factors, and outcome of arrhythmic COVID19 patients.

Methods

This was a single-centered study. All confirmed COVID19 patients admitted from May 2020 until March 2021 were included. Data were obtained from medical records. Patients with no ECG or incomplete medical record were excluded. Bivariate analysis through Chi Square was used to define association between arrhythmia risk factors, and outcomes.

Results

374 patients were included, ranged from 2 until 85 years old (mean 52.5 ± 15, median 54). Mostly were males (53.7%) with 10 days median hospice care. Fifty eight patients (15.50%) had arrhythmia, which were mainly sinus tachycardia, supraventricular tachycardia, ventricular extra systole (3.7% each) and atrial fibrillation (3.5%). Congestive heart failure (CHF) (31.9%) and hypertension (28.7%) were the main comorbid. Bivariate analysis was conducted. CHF increased risk of arrhythmia by two times (RR: 2.15, CI 95%: 1.21 – 3.83, p < 0.008) and chloroquine use by 1.17 times (RR: 1.17, CI 95%: 1.05 – 1.11, p < 0.04). Arrhythmia events increased mortality risk by 2.5 times (RR: 2.52, CI 95%: 1.41–4.48, p < 0.001). Eighteen patients (31.03%) with arrhythmia died, especially those with atrial fibrillation (7 patients).

Conclusion

Sinus tachycardia, supraventricular tachycardia, ventricular extra systole, and atrial fibrillation were the most arrhythmia found. CHF and the use of chloroquine increased risk of arrhythmia. Arrythmia itself, especially atrial fibrillation, should be monitored as it increased mortality.

Cytochrome c'β-Met Is a Variant in the P460 Superfamily Lacking the Heme-Lysyl Cross-Link: A Peroxidase Mimic Generating a Ferryl Intermediate

A defining characteristic of bacterial cytochromes (cyt's) in the P460 family is an unusual cross-link connecting the heme porphyrin to the side chain of a lysyl residue in the protein backbone. Here, via proteomics of the periplasmic fraction of the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea, we report the identification of a variant member of the P460 family that contains a methionyl residue in place of the cross-linking lysine. We formally designate this protein cytochrome "c'_β-Met" to distinguish it from other members bearing different residues at this position (e.g., cyt c'_β-Phe from the methane-oxidizing Methylococcus capsulatus Bath). As isolated, the monoheme cyt c'_β-Met is high-spin (S = ⁵/₂). Optical spectroscopy suggests that a cross-link is absent. Hydroxylamine, the substrate for the cross-linked cyt P460 from N. europaea, did not appreciably alter the optical spectrum of cyt c'_β with up to 1000-fold excess at pH 7.5. Cyt c'_β-Met did however bind 1 equiv of H₂O₂, and with a slight excess, Mössbauer spectroscopy indicated the formation of a semistable ferryl (Fe^IV═O) Compound II-like species. The corresponding electron paramagnetic resonance showed a very low intensity signal indicative of a radical at g = 2.0. Furthermore, cyt c'_β-Met exhibited guaiacol-dependent peroxidase activity (k_cat = 20.0 ± 1.2 s^-1; K_M = 2.6 ± 0.4 mM). Unlike cyt c'_β-Met, cyt P460 showed evidence of heme inactivation in the presence of 2 equiv of H₂O₂ with no appreciable guaiacol-dependent peroxidase activity. Mutagenesis of the cross-linking lysyl residue to an alanine in cyt P460, however, reversed this lack of activity.