Blastocyst implantation into the uterine endometrium establishes early pregnancy. This event is regulated by blastocyst‐ and/or endometrium‐derived molecular factors which include hormones, growth factors, cell adhesion molecules, cytokines and proteases. Their coordinated expression and function are critical for a viable pregnancy. A rate‐limiting event that immediately precedes implantation is the hatching of blastocyst. Ironically, blastocyst hatching is tacitly linked to peri‐implantation events, although it is a distinct developmental phenomenon. The exact molecular network regulating hatching is still unclear. A number of implantation‐associated molecular factors are expressed in the pre‐implanting blastocyst. Among others, cytokines, expressed by peri‐implantation blastocysts, are thought to be important for hatching, making blastocysts implantation competent. Pro‐inflammatory (IL‐6, LIF, GM‐CSF) and anti‐inflammatory (IL‐11, CSF‐1) cytokines improve hatching rates; they modulate proteases (MMPs, tPAs, cathepsins and ISP1). However, functional involvement of cytokines and their specific mediation of hatching‐associated proteases are unclear. There is a need to understand mechanistic roles of cytokines and proteases in blastocyst hatching. This review will assess the available knowledge on blastocyst‐derived pro‐inflammatory and anti‐inflammatory cytokines and their role in potentially regulating blastocyst hatching. They have implications in our understanding of early embryonic loss and infertility in mammals, including humans.

No abstract

ProblemHuman infertility affects 15–20% of reproductive‐age couples and it is mitigated by assisted reproductive technology (ART) approaches. Poor biological viability of embryos contributes to implantation failure and live birth rate (LBR). This study is aimed to examine whether or not embryo‐secreted soluble human leukocyte antigen‐G (sHLA‐G) is (i) associated with developing embryos and (ii) able to predict successful pregnancy outcome.Method of studyA retrospective, multicentric study using 539 human embryo spent medium samples (E‐SMs), analysed for sHLA‐G levels by ELISA. Correlation analysis was performed on sHLA‐G levels with developing embryonic stages, their quality scores and pregnancy outcome in terms of LBR.ResultsOf 539 E‐SMs analysed, 445 had detectable sHLA‐G (83%) with levels varying within and across clinics and, between stages of embryonic development. Levels of sHLA‐G (ng/mL) were significantly (P < .05) different in E‐SMs of cleavage‐stage embryos versus blastocysts. There was an insignificant correlation between the sHLA‐G levels and morphology scores of embryos. But, sHLA‐G levels showed a positive correlation with grades of blastocysts and importantly, its levels were significantly (P < .05) higher in live‐birth vis‐a‐vis no‐birth cases. Also, levels were higher in live‐births out of blastocysts‐ETs versus cleavage‐stage‐embryo transfers. Altered levels were observed with embryos, which resulted in miscarriages. Overall, a significant (P < .0001) association of sHLA‐G with live births was observed.ConclusionEmbryo‐derived sHLA‐G can be a valuable embryo viability, independent, biomarker, which can predict live‐birth outcome and it could be useful as an adjunct to existing criteria for elective single embryo transfer.

Among squamate reptiles, lizards exhibit an impressive array of sex-determining modes viz. genotypic sex determination, temperature-dependent sex determination, co-occurrence of both these and those that reproduce parthenogenetically. The oviparous lizard, Calotes versicolor, lacks heteromorphic sex chromosomes and there are no reports on homomorphic chromosomes. Earlier studies on this species presented little evidence to the sex-determining mechanism. Here we provide evidences for the potential role played by incubation temperature that has a significant effect (P < 0.01) on gonadal sex and sex ratio. The eggs were incubated at 14 different incubation temperatures. Interestingly, 100% males were produced at low (25.5 ± 0.5 ° C) as well as high (34 ± 0.5 ° C) incubation temperatures and 100% females were produced at low (23.5 ± 0.5 ° C) and high (31.5 ± 0.5 ° C) temperatures, clearly indicating the occurrence of TSD in this species. Sex ratios of individual clutches did not vary at any of the critical male-producing or female-producing temperatures within as well as across the seasons. However, clutch sex ratios were female- or male-biased at intermediate temperatures. Thermosensitive period occurred during the embryonic stages 30-33. Three pivotal temperatures operate producing 1:1 sex ratio. Histology of gonad and accessory reproductive structures provide additional evidence for TSD. The sex-determining pattern, observed for the first time in this species, that neither compares to Pattern I [Ia (MF) and Ib (FM)] nor to Pattern II (FMF), is being referred to as FMFM pattern of TSD. This novel FMFM pattern of sex ratio exhibited by C. versicolor may have an adaptive significance in maintaining sex ratio.

Mammalian blastocyst hatching is critically an indispensable process for successful implantation. One of the major challenges in IVF clinics is to achieve superior embryonic development with intrinsically potent hatching-competent blastocyst. However, the molecular regulation of hatching phenomenon is poorly understood. In this study, we examined the expression and function of one of the cytokines, IL-1β during blastocyst hatching in the mouse. In particular, the expression of IL-1β (Interleukin-1β), IL-1ra (Interleukin-1 receptor antagonist) and their functional receptor IL-1rt1 (Interleukin 1 receptor type-1) in morulae, zona intact- and hatched- blastocysts was studied. Supplementation of IL-1β to cultured embryos accelerated blastocyst development with improved hatching (treated: 89.6 ± 3.6% vs untreated: 65.4 ± 4.1%). When embryos were treated with IL-1ra, blastocyst hatching was decreased (treated: 28.8 ± 3.1% vs untreated: 67.5 ± 3.8%). Moreover, IL-1β and IL-1ra influenced the expression of hatching enzymes viz., implantation serine proteases (ISP 1 and ISP 2). While IL-1β increased the embryonic mRNA expression of ISPs (ISP1: 2-4; ISP2: 9-11 fold), IL-1ra decreased expression. The protein localization studies revealed increased nuclear presence predominantly of ISP 2 in IL-1β treated blastocysts. This is the first report to show the functional significance of embryonic IL-1β in regulating hatching-associated proteases, particularly ISP2. These findings have implications in our understanding of molecular regulation of blastocyst hatching and implantation failure in other species including humans.