The transcription factor GATA4 is required for follicular development and normal ovarian function.

Sex determination in mammals requires interaction between the transcription factor GATA4 and its cofactor FOG2. We have recently described the function of both proteins in testis development beyond the sex determination stage; their roles in the postnatal ovary, however, remain to be defined. Here, we use gene targeting in mice to determine the requirement of GATA4 and FOG2 in ovarian development and folliculogenesis. The results from this study identify an essential role of the GATA4 protein in the ovarian morphogenetic program. We show that in contrast to the sex determination phase, which relies on the GATA4-FOG2 complex, the subsequent regulation of ovarian differentiation is dependent upon GATA4 but not FOG2. The loss of Gata4 expression within the ovary results in impaired granulosa cell proliferation and theca cell recruitment as well as fewer primordial follicles in the ovarian cortex, causing a failure in follicular development. Preantral follicular atresia is observed within the few follicles that develop despite Gata4 deficiency. The depletion of the follicular pool in GATA4 deficient ovary results in the formation of ovarian cysts and sterility.

Cardiac expression of Tnnt1 requires the GATA4-FOG2 transcription complex.

Previous work by us and others has shown that the loss of interaction between GATA4 and FOG2 protein partners is embryonic lethal due to heart failure at embryonic day (E) 13.5; however, the role of this important protein duo in various cardiac compartments (e.g., myocardial, endocardial, or epicardial cells) remains to be understood. Although a dual role (both as an activator and a repressor) for the GATA4-FOG2 transcriptional complex has been put forward, the specific genes under GATA4-FOG2 control in the developing heart have remained largely elusive. Since the myocardial-restricted Fog2 re-expression in the Fog2 null embryos is sufficient to extend their life span, identification of GATA4-FOG2 target genes in cardiomyocytes could shed light on the molecular mechanism of GATA4-FOG2 action in these cells. We report here that cardiac expression of slow skeletal troponin T (Tnnt1) strictly depends on the physical interaction between GATA4-FOG2 in the myocardium of both atria and ventricles.

To beta or not to beta: canonical beta-catenin signaling pathway and ovarian development.

The mammalian embryonic gonad is a unique organ primordium in that it can adopt two different developmental fates-namely, differentiate as either a testis or an ovary-with dramatic consequences for an individual. While a molecular cascade culminating in testis development is well characterized, the ovarian pathways still remain enigmatic. The canonical Wnt/beta-catenin signaling implements a conserved mechanism of regulating gene expression that is integral to development of all metazoans. In this review, we summarize the recent evidence that suggests a central role for this signaling pathway in the development of the mammalian female.

Ovarian development in mice requires the GATA4-FOG2 transcription complex.

We have demonstrated previously that mammalian sexual differentiation requires both the GATA4 and FOG2 transcriptional regulators to assemble the functioning testis. Here we have determined that the sexual development of female mice is profoundly affected by the loss of GATA4-FOG2 interaction. We have also identified the Dkk1 gene, which encodes a secreted inhibitor of canonical beta-catenin signaling, as a target of GATA4-FOG2 repression in the developing ovary. The tissue-specific ablation of the beta-catenin gene in the gonads disrupts female development. In Gata4(ki/ki); Dkk1(-/-) or Fog2(-/-); Dkk1(-/-) embryos, the normal ovarian gene expression pattern is partially restored. Control of ovarian development by the GATA4-FOG2 complex presents a novel insight into the cross-talk between transcriptional regulation and extracellular signaling that occurs in ovarian development.

Serdin1/Lrrc10 is dispensable for mouse development.

We have previously identified Serdin1/Lrrc10 as a cardiac-specific message that is expressed early in murine heart development and encodes a novel leucine-rich protein. A high degree of evolutionary conservation with respect to protein sequence, cardiac-specific expression, and cis-regulatory elements suggested that LRRC10 has an important and conserved function in cardiac development. Recently, the zebrafish lrrc10 knockdown models were described with a dramatic early defect in heart looping which supported the notion that Serdin1/Lrrc10 is likely to be essential for heart development in all vertebrates. To determine Lrrc10 function in mammalian cardiac development, we have disrupted the Lrrc10 gene in mice. We report here that, in striking contrast to the zebrafish lrrc10 knockdown, Lrrc10-null mice develop normally and exhibit no discernable phenotype.

GATA4/FOG2 transcriptional complex regulates Lhx9 gene expression in murine heart development.

BACKGROUND: GATA4 and FOG2 proteins are required for normal cardiac development in mice. It has been proposed that GATA4/FOG2 transcription complex exercises its function through gene activation as well as repression; however, targets of GATA4/FOG2 action in the heart remain elusive. RESULTS: Here we report identification of the Lhx9 gene as a direct target of the GATA4/FOG2 complex. We demonstrate that the developing mouse heart normally expresses truncated isoforms of Lhx9 - Lhx9alpha and Lhx9beta, and not the Lhx9-HD isoform that encodes a protein with an intact homeodomain. At E9.5 Lhx9alpha/beta expression is prominent in the epicardial primordium, septum transversum while Lhx9-HD is absent from this tissue; in the E11.5 heart LHX9alpha/beta-positive cells are restricted to the epicardial mesothelium. Thereafter in the control hearts Lhx9alpha/beta epicardial expression is promptly down-regulated; in contrast, mouse mutants with Fog2 gene loss fail to repress Lhx9alpha/beta expression. Chromatin immunoprecipitation from the E11.5 hearts demonstrated that Lhx9 is a direct target for GATA4 and FOG2. In transient transfection studies the expression driven by the cis-regulatory regions of Lhx9 was repressed by FOG2 in the presence of intact GATA4, but not the GATA4ki mutant that is impaired in its ability to bind FOG2. CONCLUSION: In summary, the Lhx9 gene represents the first direct target of the GATA4/FOG2 repressor complex in cardiac development.

The regulation of Sox9 gene expression by the GATA4/FOG2 transcriptional complex in dominant XX sex reversal mouse models.

We have previously established an in vivo requirement for GATA4 and FOG2 transcription factors in sexual differentiation. Fog2 null mouse fetuses or fetuses homozygous for a targeted mutation in Gata4 (Gata4(ki)), which cripples the GATA4-FOG2 interaction, exhibit a profound and early block in testis differentiation in both sexes. Others have shown that XX mice with the Ods transgenic insertion or the Wt1-Sox9 YAC transgene overexpress the testis differentiation gene, Sox9. Thus, these XX animals undergo dominant sex reversal by developing into phenotypically normal, but sterile, males. Now we have determined that Fog2 haploinsufficiency prevents (suppresses) this dominant sex reversal and Fog2+/-Wt1-Sox9 or Ods XX animals develop normally--as fertile females. The suppression of sex reversal in Fog2 heterozygous females results from approximately 50% downregulation of the expression from the transgene-associated allele of Sox9. The GATA4/FOG2-dependent sex reversal observed in the transgenic XX gonads has to rely on gene targets other than the Y chromosome-linked Sry gene. Importantly, Fog2 null or Gata4(ki/ki) embryos (either XX or XY) fail to express detectable levels of Sox9 despite carrying the Ods mutation or Wt1-Sox9 transgene. Fog2 haploinsufficiency leads to a decreased amount of SOX9-positive cells in XY gonads. We conclude that FOG2 is a limiting factor in the formation of a functional GATA4/FOG2 transcription complex that is required for Sox9 expression during gonadogenesis.