Identifying genetic networks underlying myometrial transition to labor

Abstract

Background: Early transition to labor remains a major cause of infant mortality, yet the causes are largely unknown. Although several marker genes have been identified, little is known about the underlying global gene expression patterns and pathways that orchestrate these striking changes.

Results: We performed a detailed time-course study of over 9,000 genes in mouse myometrium at defined physiological states: non-pregnant, mid-gestation, late gestation, and postpartum. This dataset allowed us to identify distinct patterns of gene expression that correspond to phases of myometrial 'quiescence', 'term activation', and 'postpartum involution'. Using recently developed functional mapping tools (HOPACH (hierarchical ordered partitioning and collapsing hybrid) and GenMAPP 2.0), we have identified new potential transcriptional regulatory gene networks mediating the transition from quiescence to term activation.

Conclusions: These results implicate the myometrium as an essential regulator of endocrine hormone (cortisol and progesterone synthesis) and signaling pathways (cyclic AMP and cyclic GMP stimulation) that direct quiescence via the transcriptional upregulation of both novel and previously associated regulators. With term activation, we observe the upregulation of cytoskeletal remodeling mediators (intermediate filaments), cell junctions, transcriptional regulators, and the coordinate downregulation of negative control checkpoints of smooth muscle contractile signaling. This analysis provides new evidence of multiple parallel mechanisms of uterine contractile regulation and presents new putative targets for regulating myometrial transformation and contraction.

Figure 1

Clustering of myometrial expression profiles with HOPACH. Gene-expression profiles for 27 microarrays (vertical axis) and 4,510 probe sets (horizontal axis) are shown in the context of the HOPACH cluster map (non-pregnant data excluded). The array groups correspond to mid to late gestation (14.5, 16.5, 17.5 and 18.5 days) and postpartum (6 and 24 h). Eight clusters of genes are arranged vertically. Physiological phase groups are assigned on the basis of visual observation and association with previously associated regulators. MAPPFinder results are shown for the top-ranking distinct biological process, molecular function and cellular component groups based on a permuted p-value. Previously associated regulators of uterine quiescence and activation are indicated by a colored line next to the location of the corresponding gene probe set in the cluster map.

Figure 2

Association of quiescence and term activation pattern groups with biological pathways. Significant associations to GO classification groups and GenMAPP pathways were determined for each of the four expression pattern groups examined: Displayed are representative gene expression patterns for increased and decreased quiescence and term activation. (a) increased quiescence (yellow curve), increased activation (red curve); (b) decreased quiescence (green curve) and decreased activation (blue curve). GO terms and GenMAPP pathways highlighted by analysis with the program MAPPFinder are indicated by italicized blue text. Biological processes identified by literature association are indicated in black text. Parent biological categories are designated by bold text.

Figure 3

Analysis of pathways of uterine smooth muscle contraction. (a) Prostaglandin synthesis and (b) G-protein signaling pathways in the myometrium are overlaid with gene-expression color criterion and fold-changes from the program GenMAPP. Interactions suggested by results of this microarray analysis are included in these figures. Detailed gene-expression data, statistics and full gene annotations are available on the GenMAPP interactive version of these pathways online [40].

Figure 4

Association of genomic localization with co-regulation of expression. (a,b) Chromosomal gene clusters contain highly correlated expression changes among multiple members. Global patterns of gene expression within these genomic intervals are visualized by representing mean log expression for four of the myometrium time-point groups (non-pregnant, 14.5 and 18.5 days gestation, and 24 h postpartum), versus relative gene position on the chromosome. Gene strand orientation and position is designated by the orientation of arrows. Gene symbols above and below arrows are shown, where italicized black text indicates co-regulated genes (same HOPACH cluster) and italicized gray genes not co-regulated for (a) increased quiescence and (b) increased postpartum involution. Non-italicized gray text indicates genes not probed by the arrays.

Figure 5

Proposed maternal model of uterine-directed contractile regulation. Theoretical model based on the major gene-expression pattern groups for quiescence, term activation and postpartum involution (light gray box outline). Arrows next to gene processes and functional groups indicate the predominant direction of fold-change as indicated by HOPACH analysis. This model proposes new roles for transcriptional regulators, regulators of mRNA processing, local hormone regulation, protease activity and cell junction formation in the control of both contractile signaling and contraction propagation in the myometrium during pregnancy. A model of postpartum involution is also presented, based on additional data (see Additional data files 4-6).