NCBI Summary:
This gene, a muscle member of the immunoglobulin gene superfamily, encodes myosin light chain kinase which is a calcium/calmodulin dependent enzyme. This kinase phosphorylates myosin regulatory light chains to facilitate myosin interaction with actin filaments to produce contractile activity. This gene encodes both smooth muscle and nonmuscle isoforms. In addition, using a separate promoter in an intron in the 3' region, it encodes telokin, a small protein identical in sequence to the C-terminus of myosin light chain kinase, that is independently expressed in smooth muscle and functions to stabilize unphosphorylated myosin filaments. A pseudogene is located on the p arm of chromosome 3. Four transcript variants that produce four isoforms of the calcium/calmodulin dependent enzyme have been identified as well as two transcripts that produce two isoforms of telokin. Additional variants have been identified but lack full length transcripts. [provided by RefSeq, Jul 2008]
Luteinization, Oogenesis, Oocyte maturation, Early embryo development
Comment
Cortical mechanics and myosin-II abnormalities associated with post-ovulatory aging: Implications for functional defects in aged eggs. Mackenzie AC et al. (2016) Cellular aging of the egg following ovulation, also known as post-ovulatory aging, is associated with aberrant cortical mechanics and actomyosin cytoskeleton functions. Post-ovulatory aging is associated with dysfunction of non-muscle myosin-II, and pharmacologically-induced myosin-II dysfunction produces some of the same deficiencies observed in aged eggs. Reproductive success is reduced with delayed fertilization and when copulation or insemination occurs at increased times after ovulation. Post-ovulatory aged eggs have several abnormalities in the plasma membrane and cortex, including reduced egg membrane receptivity to sperm, aberrant sperm-induced cortical remodeling and formation of fertilization cones at the site of sperm entry, and reduced ability to establish a membrane block to prevent polyspermic fertilization. Ovulated mouse eggs were collected at 21-22 hr post-hCG (aged eggs) or at 13-14 h post-hCG (young eggs), or young eggs were treated with the myosin light chain kinase (MLCK) inhibitor ML-7, to test the hypothesis that disruption of myosin-II function could mimic some of the effects of post-ovulatory aging. Eggs were subjected to various analyses. Cytoskeletal proteins in eggs and parthenogenesis were assessed using fluorescence microscopy, with further analysis of cytoskeletal proteins in immunoblotting experiments. Cortical tension was measured through micropipette aspiration assays. Egg membrane receptivity to sperm was assessed in in vitro fertilization (IVF) assays. Membrane topography was examined by low-vacuum scanning electron microscopy. Aged eggs have decreased levels and abnormal localizations of phosphorylated myosin-II regulatory light chain (pMRLC; p=0.0062). Cortical tension, which is mediated in part by myosin-II, is reduced in aged mouse eggs as compared to young eggs, by ∼40% in the cortical region where the metaphase II spindle is sequestered, and by ∼50% in the domain to which sperm bind and fuse (p<0.0001). Aging-associated parthenogenesis is partly rescued by treating eggs with a zinc ionophore (p=0.003), as is parthenogenesis induced by inhibition of mitogen-activated kinase (MAPK) 3/1 (also known as extracellular signal-regulated kinase ERK]1/2) or MLCK. Inhibition of MLCK with ML-7 also results in effects that mimic those of post-ovulatory aging: fertilized ML-7-treated eggs show both impaired fertilization and increased extents of polyspermy, and ML-7-treated young eggs have several membrane abnormalities that are shared by post-ovulatory aged eggs. These studies were done with mouse oocytes, and it remains to be fully determined how these findings from mouse oocytes would compare to other species. For studies using methods not amenable to analysis of large sample sizes and data are limited to what images one can capture (e.g., scanning electron microscopy), data should be interpreted conservatively. These data provide insights into causes of reproductive failures at later post-copulatory times. Not applicable. This project was supported by R01 HD037696 and R01 HD045671 from the NIH to JPE. Cortical tension studies were supported by R01 GM66817 to DNR. The authors declare there are no financial conflicts of interest.//////////////////
A new model for asymmetric spindle positioning in mouse oocytes. [Schuh M et al. An oocyte matures into an egg by extruding half of the chromosomes in a small polar body. This extremely asymmetric division enables the oocyte to retain sufficient storage material for the development of the embryo after fertilization. To divide asymmetrically, mammalian oocytes relocate the spindle from their center to the cortex. In all mammalian species analyzed so far, including human, mouse, cow, pig, and hamster, spindle relocation depends on filamentous actin (F-actin). However, even though spindle relocation is essential for fertility, the involved F-actin structures and the mechanism by which they relocate the spindle are unknown. Here we show in live mouse oocytes that spindle relocation requires a continuously reorganizing cytoplasmic actin network nucleated by Formin-2 (Fmn2). We found that the spindle poles were enriched in activated myosin and pulled on this network. Inhibition of myosin activation by myosin light chain kinase (MLCK) stopped pulling and spindle relocation, indicating that myosin pulling creates the force that drives spindle movement. Based on these results, we propose the first mechanistic model for asymmetric spindle positioning in mammalian oocytes and validate five of its key predictions experimentally.
Expression regulated by
LH
Comment
Polycystic ovary syndrome (PCOS) affects 5% of reproductive aged women and is the leading cause of anovulatory infertility. A hallmark of PCOS is excessive theca cell androgen secretion, which is directly linked to the symptoms of PCOS. Our previous studies demonstrated that theca cells from PCOS ovaries maintained in long term culture persistently secrete significantly greater amounts of androgens than normal theca cells, suggesting an intrinsic abnormality. Furthermore, previous studies suggested that ovarian hyperandrogenemia is inherited as an autosomal dominant trait. However, the genes responsible for ovarian hyperandrogenemia of PCOS have not been identified. In this present study, Wood JR, et al carried out microarray analysis to define the gene networks involved in excess androgen synthesis by the PCOS theca cells in order to identify candidate PCOS genes. Analysis revealed that PCOS theca cells have a gene expression profile that is distinct from normal theca cells. Included in the cohort of genes with increased mRNA abundance in PCOS theca cells were aldehyde dehydrogenase 6 and retinol dehydrogenase 2, which play a role in all-trans-retinoic acid biosynthesis and the transcription factor GATA6. We demonstrated that retinoic acid and GATA6 increased the expression of 17alpha-hydroxylase, providing a functional link between altered gene expression and intrinsic abnormalities in PCOS theca cells. Thus, the analyses have 1) defined a stable molecular phenotype of PCOS theca cells, 2) suggested new mechanisms for excess androgen synthesis by PCOS theca cells, and 3) identified new candidate genes that may be involved in the genetic etiology of PCOS. This is one of the genes with Altered mRNA Abundance in PCOS Theca Cells as compared with normal theca cells Maintained Under Basal Conditions.
Gene expression decreased. Luteinization of porcine preovulatory follicles leads to systematic changes in follicular gene expression. Agca C et al. The LH surge initiates the luteinization of preovulatory follicles and causes hormonal and structural changes that ultimately lead to ovulation and the formation of corpora lutea. The objective of the study was to examine gene expression in ovarian follicles (n = 11) collected from pigs (Sus scrofa domestica) approaching estrus (estrogenic preovulatory follicle; n = 6 follicles from two sows) and in ovarian follicles collected from pigs on the second day of estrus (preovulatory follicles that were luteinized but had not ovulated; n = 5 follicles from two sows). The follicular status within each follicle was confirmed by follicular fluid analyses of estradiol and progesterone ratios. Microarrays were made from expressed sequence tags that were isolated from cDNA libraries of porcine ovary. Gene expression was measured by hybridization of fluorescently labeled cDNA (preovulatory estrogenic or -luteinized) to the microarray. Microarray analyses detected 107 and 43 genes whose expression was decreased or increased (respectively) during the transition from preovulatory estrogenic to -luteinized (P<0.01). Cells within preovulatory estrogenic follicles had a gene-expression profile of proliferative and metabolically active cells that were responding to oxidative stress. Cells within preovulatory luteinized follicles had a gene-expression profile of nonproliferative and migratory cells with angiogenic properties. Approximately, 40% of the discovered genes had unknown function.
Ovarian localization
Oocyte, Theca
Comment
Follicle stages
Comment
Phenotypes
Mutations
1 mutations
Species: mouse
Mutation name: type: null mutation fertility: infertile - non-ovarian defect Comment: Deletion of Mylk1 in Oocytes Causes Delayed Morula-to-Blastocyst Transition and Reduced Fertility Without Affecting Folliculogenesis and Oocyte Maturation in Mice. Liang QX et al. (2015) Mammalian oocyte undergos two asymmetric cell divisions during meiotic maturation and fertilization. Acentric spindle positioning and cortical polarity are major factors involved in asymmetric cell division, both of which are thought to depend on the dynamic interaction between myosin II and actin filaments. Myosin light chain kinase (MLCK) encoding by Mylk1 gene could directly phosphorylate and activate myosin II. To determine whether MLCK was required for oocyte asymmetric division, we specifically disrupted Mylk1 gene in oocytes by Cre-loxP conditional knockout system. We found that Mylk1 mutant female mice showed severe subfertility. Unexpectedly, contrary to previously reported in vitro findings, our data showed that oocyte meiotic maturation including spindle organization, polarity establishment, homologous chromosomes separation and polar body extrusion were not affected in Mylk1(fl/fl);GCre(+) females. Follicular development, ovulation and early embryonic develop to compact morula occurred normally in Mylk1(fl/fl);GCre(+) females, but deletion of MLCK caused delayed morula-to-blastocyst transition. More than a third of embryos were at morula stage at 3.5 days post coitum (dpc) in vivo. The delayed embryos could develop further to early blastocyst stage in vitro on Day 4 when most control embryos reached expanded blastocysts. Our findings provide evidence that MLCK is linked to timely blastocyst formation, though it is dispensable for oocyte meiotic maturation.//////////////////