An alternative splicing switch regulates embryonic stem cell pluripotency and reprogramming.

Alternative splicing (AS) is a key process underlying the expansion of proteomic diversity and the regulation of gene expression. Here, we identify an evolutionarily conserved embryonic stem cell (ESC)-specific AS event that changes the DNA-binding preference of the forkhead family transcription factor FOXP1. We show that the ESC-specific isoform of FOXP1 stimulates the expression of transcription factor genes required for pluripotency, including OCT4, NANOG, NR5A2, and GDF3, while concomitantly repressing genes required for ESC differentiation. This isoform also promotes the maintenance of ESC pluripotency and contributes to efficient reprogramming of somatic cells into induced pluripotent stem cells. These results reveal a pivotal role for an AS event in the regulation of pluripotency through the control of critical ESC-specific transcriptional programs.

Antisense RNA regulates glutamine synthetase in a heterocyst-forming cyanobacterium.

Glutamine synthetase (GS) is a key enzyme involved in nitrogen assimilation and the maintenance of C/N balance, and it is strictly regulated in all bacteria. In cyanobacteria, glutamine synthetase expression is controlled by nitrogen control A (NtcA) transcription factor, which operates global nitrogen regulation in these photosynthetic organisms. Furthermore, post-translational regulation of GS is operated by protein-protein interaction with GS inactivating factors (IFs). Here, we describe an additional regulatory mechanism involving an antisense RNA. In Nostoc sp. PCC 7120, the GS inactivating factor A (gifA) gene (encoding GS inactivating factor IF7) is transcribed downstream of the glutamine synthetase (glnA) gene, from the opposite strand, and the gifA mRNA extends into the glnA coding sequence in antisense orientation. Therefore, the dual RNA transcript that encodes gifA constitutes two functional regions: a 5' protein-coding region, encoding IF7, and a 3' untranslated region that acts as an antisense to glnA. By increasing the levels of such antisense RNA either in cis or in trans, we demonstrate that the amount of GS activity can be modulated by the presence of the antisense RNA. The tail-to-tail disposition of the glnA and gifA genes observed in many cyanobacterial strains from the Nostocales clade suggests the prevalence of such antisense RNA-mediated regulation of GS in this group of cyanobacteria.

An abstract categorical decision code in dorsal premotor cortex.

The dorsal premotor cortex (DPC) has classically been associated with a role in preparing and executing the physical motor variables during cognitive tasks. While recent work has provided nuanced insights into this role, here we propose that DPC also participates more actively in decision-making. We recorded neuronal activity in DPC while two trained monkeys performed a vibrotactile categorization task, utilizing two partially overlapping ranges of stimulus values that varied on two physical attributes: vibrotactile frequency and amplitude. We observed a broad heterogeneity across DPC neurons, the majority of which maintained the same response patterns across attributes and ranges, coding in the same periods, mixing temporal and categorical dynamics. The predominant categorical signal was maintained throughout the delay, movement periods and notably during the intertrial period. Putting the entire population's data through two dimensionality reduction techniques, we found strong temporal and categorical representations without remnants of the stimuli's physical parameters. Furthermore, projecting the activity of one population over the population axes of the other yielded identical categorical and temporal responses. Finally, we sought to identify functional subpopulations based on the combined activity of all stimuli, neurons, and time points; however, we found that single-unit responses mixed temporal and categorical dynamics and couldn't be clustered. All these point to DPC playing a more decision-related role than previously anticipated.

Hierarchical unimodal processing within the primary somatosensory cortex during a bimodal detection task.

Do sensory cortices process more than one sensory modality? To answer these questions, scientists have generated a wide variety of studies at distinct space-time scales in different animal models, and often shown contradictory conclusions. Some conclude that this process occurs in early sensory cortices, but others that this occurs in areas central to sensory cortices. Here, we sought to determine whether sensory neurons process and encode physical stimulus properties of different modalities (tactile and acoustic). For this, we designed a bimodal detection task where the senses of touch and hearing compete from trial to trial. Two Rhesus monkeys performed this novel task, while neural activity was recorded in areas 3b and 1 of the primary somatosensory cortex (S1). We analyzed neurons' coding properties and variability, organizing them by their receptive field's position relative to the stimulation zone. Our results indicate that neurons of areas 3b and 1 are unimodal, encoding only the tactile modality in both the firing rate and variability. Moreover, we found that neurons in area 3b carried more information about the periodic stimulus structure than those in area 1, possessed lower response and coding latencies, and had a lower intrinsic time scale. In sum, these differences reveal a hidden processing-based hierarchy. Finally, using a powerful nonlinear dimensionality reduction algorithm, we show that the activity from areas 3b and 1 can be separated, establishing a clear division in the functionality of these two subareas of S1.

Invariant timescale hierarchy across the cortical somatosensory network.

The ability of cortical networks to integrate information from different sources is essential for cognitive processes. On one hand, sensory areas exhibit fast dynamics often phase-locked to stimulation; on the other hand, frontal lobe areas with slow response latencies to stimuli must integrate and maintain information for longer periods. Thus, cortical areas may require different timescales depending on their functional role. Studying the cortical somatosensory network while monkeys discriminated between two vibrotactile stimulus patterns, we found that a hierarchical order could be established across cortical areas based on their intrinsic timescales. Further, even though subareas (areas 3b, 1, and 2) of the primary somatosensory (S1) cortex exhibit analogous firing rate responses, a clear differentiation was observed in their timescales. Importantly, we observed that this inherent timescale hierarchy was invariant between task contexts (demanding vs. nondemanding). Even if task context severely affected neural coding in cortical areas downstream to S1, their timescales remained unaffected. Moreover, we found that these time constants were invariant across neurons with different latencies or coding. Although neurons had completely different dynamics, they all exhibited comparable timescales within each cortical area. Our results suggest that this measure is demonstrative of an inherent characteristic of each cortical area, is not a dynamical feature of individual neurons, and does not depend on task demands.

Low-Cost EEG Multi-Subject Recording Platform for the Assessment of Students' Attention and the Estimation of Academic Performance in Secondary School.

The level of student attention in class greatly affects their academic performance. Teachers typically rely on visual inspection to react to students' attention in time, but this subjective method leads to inconsistencies across classes. Online education exacerbates the issue as students can turn off cameras and microphones to keep their own privacy. To address this, we present a novel, low-cost EEG-based platform for assessing students' attention and estimating their academic performance. In a study involving 34 secondary school students (aged 14 to 16), participants watched an academic video and answered evaluation questions while their EEG activity was recorded using a commercial headset. The results demonstrate a significant correlation (0.53, p-value = 0.003) between the power spectral density (PSD) of the EEG beta band (12-30 Hz) and students' academic performance. Additionally, there was a notable difference in PSD-beta between high and low academic performers. These findings encourage the use of PSD-beta for the immediate and objective assessment of both the student attention and the subsequent academic performance. The platform offers valuable and objective feedback to teachers, enhancing the effectiveness of both face-to-face and online teaching and learning environments.

Use of Private Sector Workforce Respiratory Disease Short-Term Disability Claims to Assess SARS-CoV-2, Mexico, 2020.

We examined respiratory disease short-term disability claims submitted to the Mexican Social Security Institute during 2020. A total of 1,631,587 claims were submitted by 19.1 million insured workers. Cumulative incidence (8.5%) was 3.6 times higher than that for January 2015‒December-2019. Workers in healthcare, social assistance, self-service, and retail stores were disproportionately affected.

Quantitative Proteomics at Early Stages of the Symbiotic Interaction Between Oryza sativa and Nostoc punctiforme Reveals Novel Proteins Involved in the Symbiotic Crosstalk.

Symbiosis between cyanobacteria and plants is considered pivotal for biological nitrogen deposition in terrestrial ecosystems. Despite extensive knowledge of the ecology of plant-cyanobacterium symbioses, little is known about the molecular mechanisms involved in recognition between partners. Here, we conducted a quantitative sequential window acquisition of all theoretical fragment ion spectra mass spectrometry pipeline to analyze protein changes in Oryza sativa and Nostoc punctiforme during early events of symbiosis. We found differentially expressed proteins in both organisms linked to several biological functions, including signal transduction, adhesion, defense-related proteins and cell wall modification. In N. punctiforme we found increased expression of 62 proteins that have been previously described in other Nostoc-plant symbioses, reinforcing the robustness of our study. Our findings reveal new proteins activated in the early stages of the Nostoc-Oryza symbiosis that might be important for the recognition between the plant and the host. Oryza mutants in genes in the common symbiosis signaling pathway (CSSP) show reduced colonization efficiency, providing first insights on the involvement of the CSSP for the accommodation of N. punctiforme inside the plant cells. This information may have long-term implications for a greater understanding of the symbiotic interaction between Nostoc and land plants.

A nitrogen stress-inducible small RNA regulates CO2 fixation in Nostoc.

In the absence of fixed nitrogen, some filamentous cyanobacteria differentiate heterocysts, specialized cells devoted to fixing atmospheric nitrogen (N2). This differentiation process is controlled by the global nitrogen regulator NtcA and involves extensive metabolic reprogramming, including shutdown of photosynthetic CO2 fixation in heterocysts, to provide a microaerobic environment suitable for N2 fixation. Small regulatory RNAs (sRNAs) are major post-transcriptional regulators of gene expression in bacteria. In cyanobacteria, responding to nitrogen deficiency involves transcribing several nitrogen-regulated sRNAs. Here, we describe the participation of nitrogen stress-inducible RNA 4 (NsiR4) in post-transcriptionally regulating the expression of two genes involved in CO2 fixation via the Calvin cycle: glpX, which encodes bifunctional sedoheptulose-1,7-bisphosphatase/fructose-1,6-bisphosphatase (SBPase), and pgk, which encodes phosphoglycerate kinase (PGK). Using a heterologous reporter assay in Escherichia coli, we show that NsiR4 interacts with the 5'-untranslated region (5'-UTR) of glpX and pgk mRNAs. Overexpressing NsiR4 in Nostoc sp. PCC 7120 resulted in a reduced amount of SBPase protein and reduced PGK activity, as well as reduced levels of both glpX and pgk mRNAs, further supporting that NsiR4 negatively regulates these two enzymes. In addition, using a gfp fusion to the nsiR4 promoter, we show stronger expression of NsiR4 in heterocysts than in vegetative cells, which could contribute to the heterocyst-specific shutdown of Calvin cycle flux. Post-transcriptional regulation of two Calvin cycle enzymes by NsiR4, a nitrogen-regulated sRNA, represents an additional link between nitrogen control and CO2 assimilation.

Navigable Space and Traversable Edges Differentially Influence Reorientation in Sighted and Blind Mice.

Reorientation enables navigators to regain their bearings after becoming lost. Disoriented individuals primarily reorient themselves using the geometry of a layout, even when other informative cues, such as landmarks, are present. Yet the specific strategies that animals use to determine geometry are unclear. Moreover, because vision allows subjects to rapidly form precise representations of objects and background, it is unknown whether it has a deterministic role in the use of geometry. In this study, we tested sighted and congenitally blind mice (Ns = 8-11) in various settings in which global shape parameters were manipulated. Results indicated that the navigational affordances of the context-the traversable space-promote sampling of boundaries, which determines the effective use of geometric strategies in both sighted and blind mice. However, blind animals can also effectively reorient themselves using 3D edges by extensively patrolling the borders, even when the traversable space is not limited by these boundaries.

Role of obesity and blood pressure in epicardial adipose tissue thickness in children.

BACKGROUND: Elevated body mass index (BMI) has been associated with cardiac changes, such as higher epicardial adipose tissue (EAT) thickness. This fat has been identified as a predictive factor of cardiovascular diseases during adulthood. However, few studies have tested the association of multiple cardiovascular risk factors (high weight or blood pressure) with EAT in adolescents and children. Therefore, the main objective of this current research was to determine the impact of BMI, overweight, obesity, and blood pressure on EAT thickness in children. METHODS: A descriptive cross-sectional study focused on elementary and high school students aged 6-16 years was carried out by utilizing diverse measurements and instruments, such as echocardiography. RESULTS: EAT thickness (N = 228) was linked to sex (more predominant in boys 2.3 ± 0.6; p = 0.044), obesity (2.3 ± 0.6; p < 0.001), and hypertension (2.6 ± 0.6; p = 0.036). The logistic regression indicated that age, sex, and BMI seemed to be more relevant factors in EAT thickness in children (adjusted R square = 0.22; p < 0.001). CONCLUSIONS: This paper examined the associations of sex, age, and cardiovascular risk factors (arthrometric measures and blood pressure) with EAT thickness, indicating that it is necessary to assess whether the findings are associated with future events. IMPACT: Excessive weight gain and blood pressure in the early stages of life have been associated with adipose tissue. This increase in weight and blood pressure has been attributed to alterations in the epicardial adipose tissue linked to anthropometric markers in adults, but no related study has been implemented in Spanish children. This study revealed how higher epicardial adipose tissue is linked to body mass index, other anthropometric parameters, and blood pressure in Spanish children. These measurements are related to high epicardial adipose tissue thickness, which in early stages does not imply pathology but increases the risk of developing cardiovascular diseases.

Temporal signals underlying a cognitive process in the dorsal premotor cortex.

During discrimination between two sequential vibrotactile stimulus patterns, the primate dorsal premotor cortex (DPC) neurons exhibit a complex repertoire of coding dynamics associated with the working memory, comparison, and decision components of this task. In addition, these neurons and neurons with no coding responses show complex strong fluctuations in their firing rate associated with the temporal sequence of task events. Here, to make sense of this temporal complexity, we extracted the temporal signals that were latent in the population. We found a strong link between the individual and population response, suggesting a common neural substrate. Notably, in contrast to coding dynamics, these time-dependent responses were unaffected during error trials. However, in a nondemanding task in which monkeys did not require discrimination for reward, these time-dependent signals were largely reduced and changed. These results suggest that temporal dynamics in DPC reflect the underlying cognitive processes of this task.

Feed-forward information and zero-lag synchronization in the sensory thalamocortical circuit are modulated during stimulus perception.

The direction of functional information flow in the sensory thalamocortical circuit may play a role in stimulus perception, but, surprisingly, this process is poorly understood. We addressed this problem by evaluating a directional information measure between simultaneously recorded neurons from somatosensory thalamus (ventral posterolateral nucleus, VPL) and somatosensory cortex (S1) sharing the same cutaneous receptive field while monkeys judged the presence or absence of a tactile stimulus. During stimulus presence, feed-forward information (VPL → S1) increased as a function of the stimulus amplitude, while pure feed-back information (S1 → VPL) was unaffected. In parallel, zero-lag interaction emerged with increasing stimulus amplitude, reflecting externally driven thalamocortical synchronization during stimulus processing. Furthermore, VPL → S1 information decreased during error trials. Also, VPL → S1 and zero-lag interaction decreased when monkeys were not required to report the stimulus presence. These findings provide evidence that both the direction of information flow and the instant synchronization in the sensory thalamocortical circuit play a role in stimulus perception.

Pulsatile vessel at the posterior bladder wall: A new sonographic marker for placenta percreta.

OBJECTIVE: We investigated using "pulsatile vessels at the posterior bladder wall" as a novel sonographic marker to demonstrate the severity of placenta accreta spectrum (PAS). METHODS: This observational case-control study of 30 pregnant women was performed at Hackensack Meridian Health's Center for Abnormal Placentation in 2020. The case group was made up of women with historically described sonographic signs of PAS and was compared against two control groups: (1) women with uncomplicated placenta previa and (2) women with no evidence of placenta previa sonographically. All patients were evaluated with Color Flow Doppler ultrasound to assess the presence of arterial vessels at the posterior bladder wall. The flow characteristics and resistance indices (RI) were noted in the presence of pulsatile vessels. All patients' placentation was clinically confirmed at delivery. Patients with clinical invasive placentation underwent histopathological diagnosis to confirm disease presence. RESULTS: Hundred percent of subjects in our series with suspected PAS exhibited pulsatile arterial vessels at the posterior bladder wall sonographically with a low RI of 0.38 ± 0.1 at an average of 24.6 ± 5.2 gestational weeks. Cases were histopathologically confirmed to have placenta percreta after delivery. Patients in either of the control groups did not display pulsatile vessels at the posterior bladder wall during antenatal sonographic evaluations and had no clinical evidence of PAS. CONCLUSION: The presence of posterior urinary bladder wall pulsatile arterial vessels with low RI, in addition to traditional sonographic markers increases the suspicion of severe PAS. Thus, these findings allow for the greater opportunity for coordination of patient care prior to delivery.

High prevalence of SARS-CoV-2 detection and prolonged viral shedding in stools: A systematic review and cohort study.

OBJECTIVES: To: 1. Describe the frequency of viral RNA detection in stools in a cohort of patients infected with SARS-CoV-2, and 2. Perform a systematic review to assess the clearance time in stools of SARS-CoV-2. METHODS: We conducted a prospective cohort study in two centers between March and May 2020. We included SARS-CoV-2 infected patients of any age and severity. We collected seriated nasopharyngeal swabs and stool samples to detect SARS-CoV-2. After, we performed a systematic review of the prevalence and clearance of SARS-CoV-2 in stools (PROSPERO-ID: CRD42020192490). We estimated prevalence using a random-effects model. We assessed clearance time by using Kaplan-Meier curves. RESULTS: We included 32 patients; mean age was 43.7±17.7 years, 43.8% were female, and 40.6% reported gastrointestinal symptoms. Twenty-five percent (8/32) of patients had detectable viral RNA in stools. The median clearance time in stools of the cohort was 11[10-15] days. Systematic review included 30 studies (1392 patients) with stool samples. Six studies were performed in children and 55% were male. The pooled prevalence of viral detection in stools was 34.6% (twenty-four studies, 1393 patients; 95%CI:25.4-45.1); heterogeneity was high (I2:91.2%, Q:208.6; p≤0.001). A meta-regression demonstrates an association between female-gender and lower presence in stools (p=0.004). The median clearance time in stools was 22 days (nineteen studies, 140 patients; 95%CI:19-25). After 34 days, 19.9% (95%CI:11.3-29.7) of patients have a persistent detection in stools. CONCLUSIONS: Detection of SARS-CoV-2 in stools is a frequent finding. The clearance of SARS-CoV-2 in stools is prolonged and it takes longer than nasopharyngeal secretions.

Individualised luteal phase support in artificially prepared frozen embryo transfer cycles based on serum progesterone levels: a prospective cohort study.

STUDY QUESTION: Does an individualised luteal phase support (iLPS), according to serum progesterone (P4) level the day prior to euploid frozen embryo transfer (FET), improve pregnancy outcomes when started on the day previous to embryo transfer? SUMMARY ANSWER: Patients with low serum P4 the day prior to euploid FET can benefit from the addition of daily subcutaneous P4 injections (Psc), when started the day prior to FET, and achieve similar reproductive outcomes compared to those with initial adequate P4 levels. WHAT IS KNOWN ALREADY: The ratio between FET/IVF has spectacularly increased in the last years mainly thanks to the pursuit of an ovarian hyperstimulation syndrome free clinic and the development of preimplantation genetic testing (PGT). There is currently a big concern regarding the endometrial preparation for FET, especially in relation to serum P4 levels around the time of embryo transfer. Several studies have described impaired pregnancy outcomes in those patients with low P4 levels around the time of FET, considering 10 ng/ml as one of the most accepted reference values. To date, no prospective study has been designed to compare the reproductive outcomes between patients with adequate P4 the day previous to euploid FET and those with low, but restored P4 levels on the transfer day after iLPS through daily Psc started on the day previous to FET. STUDY DESIGN, SIZE, DURATION: A prospective observational study was conducted at a university-affiliated fertility centre between November 2018 and January 2020 in patients undergoing PGT for aneuploidies (PGT-A) IVF cycles and a subsequent FET under hormone replacement treatment (HRT). A total of 574 cycles (453 patients) were analysed: 348 cycles (leading to 342 euploid FET) with adequate P4 on the day previous to FET, and 226 cycles (leading to 220 euploid FET) under iLPS after low P4 on the previous day to FET, but restored P4 levels on the transfer day. PARTICIPANTS/MATERIALS, SETTING, METHODS: Overall we included 574 HRT FET cycles (453 patients). Standard HRT was used for endometrial preparation. P4 levels were measured the day previous to euploid FET. P4 > 10.6 ng/ml was considered as adequate and euploid FET was performed on the following day (FET Group 1). P4 < 10.6 ng/ml was considered as low, iLPS was added in the form of daily Psc injections, and a new P4 analysis was performed on the following day. FET was only performed on the same day when a restored P4 > 10.6 ng/ml was achieved (98.2% of cases) (FET Group 2). MAIN RESULTS AND THE ROLE OF CHANCE: Patient's demographics and cycle parameters were comparable between both euploid FET groups (FET Group 1 and FET Group 2) in terms of age, weight, oestradiol and P4 levels and number of embryos transferred. No statistically significant differences were found in terms of clinical pregnancy rate (56.4% vs 59.1%: rate difference (RD) -2.7%, 95% CI [-11.4; 6.0]), ongoing pregnancy rate (49.4% vs 53.6%: RD -4.2%, 95% CI [-13.1; 4.7]) or live birth rate (49.1% vs 52.3%: RD -3.2%, 95% CI [-12; 5.7]). No significant differences were also found according to miscarriage rate (12.4% vs 9.2%: RD 3.2%, 95% CI [-4.3; 10.7]). LIMITATIONS, REASONS FOR CAUTION: Only iLPS through daily Psc was evaluated. The time for Psc injection was not stated and no serum P4 determinations were performed once the pregnancy was achieved. WIDER IMPLICATIONS OF THE FINDINGS: Our study provides information regarding an 'opportunity window' for improved ongoing pregnancy rates and miscarriage rates through a daily Psc injection in cases of inadequate P4 levels the day previous to FET (P4 < 10.6 ng/ml) and restored values the day of FET (P4 > 10.6 ng/ml). Only euploid FET under HRT were considered, avoiding one of the main reasons of miscarriage and implantation failure and overcoming confounding factors such as female age, embryo quality or ovarian stimulation protocols. STUDY FUNDING/COMPETING INTEREST(S): No external funding was received. B.C. reports personal fees from MSD, Merck Serono, Ferring Pharmaceuticals, IBSA and Gedeon Richter outside the submitted work. N.P. reports grants and personal fees from MSD, Merck Serono, Ferring Pharmaceuticals, Theramex and Besins International and personal fees from IBSA and Gedeon Richter outside the submitted work. The remaining authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER: NCT03740568.

Comportamiento epidemiológico de SARS-CoV-2 en población trabajadora afiliada al Instituto Mexicano del Seguro Social.

Objetivo. Describir el comportamiento de la epidemia de SARS-CoV-2 entre los trabajadores afiliados al Instituto Mexicano del Seguro Social (IMSS). Material y métodos. Se analizaron las incapacidades temporales para el trabajo por enfermedades respiratorias (ITT-ER), las hospitalizaciones y defunciones asociadas durante el periodo del 1 marzo al 31 diciembre 2020. Se estimó la tasa de ataque (TA) por SARS-CoV-2, así como los riesgos relativos (RR) de ITT-ER, hos-pitalización y defunción. Resultados. De los trabajadores afiliados al IMSS, 8.8% (n=1 730 334) recibió al menos una ITT-ER. La TA fue mayor en mujeres y en ambos sexos fue menor en el grupo de >60 años. Los RR de hospitalización y defunción fueron mayores en hombres y aumentaron con la edad. Comparado con las ITT-ER de 2015-2019, Durango, Tamaulipas y Nuevo León tuvieron un RR mayor de ITT-ER que el resto del país. Conclusiones. La epidemia de SARS-CoV-2 tuvo repercusiones importantes en los trabajadores afiliados al IMSS; se observó un exceso de ITT-ER de 4.6 veces respecto a la frecuencia esperada y cerca de un millón de casos de SARS-CoV-2. Los datos sugieren que el sistema de ITT-ER puede ser utilizado como elemento adicional para la vigilancia epidemiológica de enfermedades emergentes.

NsiR1, a small RNA with multiple copies, modulates heterocyst differentiation in the cyanobacterium Nostoc sp. PCC 7120.

Upon nitrogen starvation, filamentous cyanobacteria develop heterocysts, specialized cells devoted to the fixation of atmospheric nitrogen. Differentiation of heterocyst at semi-regular intervals along the filaments requires complex structural and functional changes that are under the control of the master transcriptional regulator HetR. NsiR1 (nitrogen stress-induced RNA 1) is a HetR-dependent non-coding RNA that is expressed specifically in heterocysts from a very early stage of differentiation. In the genome of Nostoc sp. PCC 7120 there are 12 tandem copies of nsiR1 (nsiR1.1 to nsiR1.12), seven of them with identical sequence (nsiR1.3 to nsiR1.9) and the others slightly divergent. nsiR1.1 is transcribed antisense to the 5' UTR of hetF, a gene required for heterocyst development. Here, we show that binding of NsiR1.1 inhibits translation of the hetF mRNA by inducing structural changes in its 5' UTR. Altered levels of NsiR1 result in different phenotypic alterations including enlarged cell size and delayed heterocyst development that could be related to a reduced amount of HetF.

Low progesterone levels on the day before natural cycle frozen embryo transfer are negatively associated with live birth rates.

STUDY QUESTION: Are progesterone (P) levels on the day before natural cycle frozen embryo transfer (NC-FET) associated with live birth rate (LBR)? SUMMARY ANSWER: Regular ovulatory women undergoing NC-FET with serum P levels <10 ng/ml on the day before blastocyst transfer have a significantly lower LBR than those with serum P levels >10 ng/ml. WHAT IS KNOWN ALREADY: The importance of serum P levels around the time of embryo transfer in patients undergoing FET under artificial endometrial preparation has been well established. However, no study has analyzed the importance of serum P levels in patients undergoing FET under a true natural endometrial preparation cycle. STUDY DESIGN, SIZE, DURATION: This was a retrospective cohort study including 294 frozen blastocyst transfers under natural cycle endometrial preparation at a university-affiliated fertility centre between January 2016 and January 2019. PARTICIPANTS/MATERIALS, SETTING, METHODS: All patients had regular menstrual cycles and underwent NC-FET with their own oocytes. Only patients who had undergone serum P measurement between 8 am and 11 am on the day before FET were included. Patients did not receive any external medication for endometrial preparation or luteal phase support. Patients were divided into two groups according to serum P levels below or above 10 ng/ml on the day before FET. Univariate analysis was carried out to describe and compare the cycle characteristics with reproductive outcomes. To evaluate the effect of P, a multivariable logistic model was fitted for each outcome after adjusting for confounding variables. MAIN RESULTS AND THE ROLE OF CHANCE: Mean serum P levels on the day before FET were significantly higher in patients who had a live birth compared to those who did not (14.5 ± 7.0 vs 12.0 ± 6.6 ng/ml, 95% CI [0.83; 4.12]). The overall clinical pregnancy rate (CPR) and LBR were 42.9% and 35.4%, respectively. Patients in the higher P group (>10 ng/ml) had a higher LBR (41.1% vs 25.7%: risk difference (RD) 15.4%, 95% CI [5; 26]) and CPR (48.6% vs 33.0%: RD 15.6%, 95% CI [4; 27]). Patients with higher serum P levels on the day before FET (63% of patients) had an improved LBR (odds ratio: 1.05; 95% CI [1.02; 1.09]). Women with serum P levels <10 ng/ml on the day before FET (37% of patients) had significantly higher weights (62.5 ± 9.9 vs 58.1 ± 7.1 kg, 95% CI [1.92; 6.90]) and BMI (22.9 ± 3.6 vs 21.6 ± 2.7 kg/m2, 95% CI [0.42; 2.25]) compared to patients with P levels >10 ng/ml. LIMITATIONS, REASONS FOR CAUTION: The main limitation of our study is its retrospective design. Other potential limitations are the detection of LH surge through urine testing and the inclusion of patients who did and did not undergo preimplantation genetic testing for aneuploidies. The protocol used in our institution for monitoring NC-FET does not look for the onset of progesterone secretion by the corpus luteum, and a slow luteinisation process or delay of corpus luteum function cannot be ruled out. WIDER IMPLICATIONS OF THE FINDINGS: We provide evidence that a minimum serum P threshold (P >10 ng/ml) might be required for improved reproductive outcomes in NC-FET. This result suggests that there are different mechanisms by which P is produced and/or distributed by each patient. This study also provides an excellent model to evaluate the impact of luteal phase defect through NC-FET. A prospective evaluation to assess whether P supplementation should be individualised according to patient's needs is necessary to support our findings. STUDY FUNDING/COMPETING INTEREST(S): No external funding was used, and there are no competing interests.

Factors associated with serum progesterone concentrations the day before cryopreserved embryo transfer in artificial cycles.

RESEARCH QUESTION: What factors determine serum progesterone concentrations the day before cryopreserved embryo transfer in artificially prepared cycles? DESIGN: Retrospective cohort study at a university-affiliated fertility centre including infertile women under 45 years old using own oocytes who underwent a total of 685 single cryopreserved blastocyst transfers under hormonal therapy. Determinants that affected live birth rate (LBR) were analysed using a multivariate logistic regression. Univariate analysis and multivariate linear regression were used to evaluate independent factors that affect serum progesterone concentrations. RESULTS: Age (odds ratio [OR] 0.93; 95% confidence interval [CI] 0.89-0.96), duration of oestradiol (OR 0.96; 95% CI 0.92-0.99), serum progesterone concentrations (OR 1.04; 95% CI 1.01-1.08) and patients who underwent preimplantation genetic testing for aneuploidies (PGT-A) (OR 2.17; 95% CI 1.55-3.03) were independently associated with LBR. After univariate analysis, determinants of progesterone concentrations were: age, weight, history of a previous cryopreserved embryo transfer with serum progesterone concentrations <10 ng/ml, and time of blood extraction. The multivariate linear regression showed that increasing age presented a positive correlation with progesterone concentrations (ß = 0.11; 95% CI 0.01-0.20). On the contrary, significant negative correlations with progesterone concentrations were shown for a previous history of serum progesterone value <10 ng/ml (ß = -3.13; 95% CI -4.45 to -1.81]), higher weight (ß = -0.05; 95% CI -0.08 to -0.01) and the time of blood sampling during the day (ß = -0.13; 95% CI -0.25 to -0.01). CONCLUSIONS: This study adds more evidence regarding the importance of serum progesterone concentrations before frozen embryo transfer (FET). It also showed that body weight, age, time of blood sampling and a history of low progesterone are determinants associated with progesterone concentrations before blastocyst FET.