Intensity mapping, which images a single spectral line from unresolved galaxies across cosmological volumes, is a promising technique for probing the early universe. Here we present predictions for the intensity map and power spectrum of the CO(1-0) line from galaxies at z ∼ 2.4-2.8, based on a parameterized model for the galaxy-halo connection, and demonstrate the extent to which properties of high-redshift galaxies can be directly inferred from such observations. We find that our fiducial prediction should be detectable by a realistic experiment. Motivated by significant modeling uncertainties, we demonstrate the effect on the power spectrum of varying each parameter in our model. Using simulated observations, we infer constraints on our model parameter space with an MCMC procedure, and show corresponding constraints on the L IR -L CO relation and the CO luminosity function. These constraints would be complementary to current high-redshift galaxy observations, which can detect the brightest galaxies but not complete samples from the faint end of the luminosity function. By probing these populations in aggregate, CO intensity mapping could be a valuable tool for probing molecular gas and its relation to star formation in high-redshift galaxies.

The ␥ subunit of the Na,K-ATPase, a 7-kDa single-span membrane protein, is a member of the FXYD gene family. Several FXYD proteins have been shown to bind to Na,K-ATPase and modulate its properties, and each FXYD protein appears to alter enzyme kinetics differently. Different results have sometimes been obtained with different experimental systems, however. To test for effects of ␥ in a native tissue environment, mice lacking a functional ␥ subunit gene (Fxyd2) were generated. These mice were viable and without observable pathology. Prior work in the mouse embryo showed that ␥ is expressed at the blastocyst stage. However, there was no delay in blastocele formation, and the expected Mendelian ratios of offspring were obtained even with Fxyd2 ؊/؊ dams. In adult Fxyd2 ؊/؊ mouse kidney, splice variants of ␥ that have different nephron segment-specific expression patterns were absent. Purified ␥-deficient renal Na,K-ATPase displayed higher apparent affinity for Na ؉ without significant change in apparent affinity for K ؉ . Affinity for ATP, which was expected to be decreased, was instead slightly increased. The results suggest that regulation of Na ؉ sensitivity is a major functional role for this protein, whereas regulation of ATP affinity may be context-specific. Most importantly, this implies that ␥ and other FXYD proteins have their effects by local and not global conformation change. Na,K-ATPase lacking the ␥ subunit had increased thermal lability. Combined with other evidence that ␥ participates in an early step of thermal denaturation, this indicates that FXYD proteins may play an important structural role in the enzyme complex.

Connexin43 (Cx43, encoded by Gja1) is required for ovarian follicle development in the mouse. It is strongly expressed in granulosa cells, in which it forms intercellular gap junction channels that couple the cells metabolically. However, recent evidence indicates that undocked gap junction hemichannels can also have physiological roles such as mediating the release of small messenger molecules, including ATP. In this study, the presence of undocked Cx43 hemichannels in granulosa cells was revealed by dye uptake induced either by mechanical stimulation or by the reduction of extracellular divalent cations, both of which are known triggers for hemichannel opening. ATP release was also detected, and could be abolished by connexin-channel blockers. None of these putative hemichannel-mediated activities were detected in Cx43-deficient granulosa cells. Therefore, we hypothesized that hemichannels account for the essential role of Cx43 in folliculogenesis. To test this, a Cx43 mutant lacking the conserved cysteines on the extracellular loops (cys-less Cx43), reported to form hemichannels but not intercellular channels, was retrovirally expressed in Cx43-deficient granulosa cells. The infected cells were then combined with wild-type oocytes to make reaggregated ovaries, which were grafted into host kidneys. Although re-introduction of wild-type Cx43 rescued folliculogenesis, introduction of cys-less Cx43 did not. Therefore, although Cx43 gap junction hemichannels might play a role in ovarian folliculogenesis, their contribution does not supplant the need for intercellular gap junction channels.

Mammalian oocytes and surrounding granulosa cells are metabolically coupled via gap junctions. In growing follicles of the mouse, gap junctions between oocytes and granulosa cells are assembled from connexin 37 (Cx37, encoded by Gja4), whereas those between granulosa cells are assembled from connexin 43 (Cx43, encoded by Gja1). This spatial separation, and the different permeability properties of gap junctions composed of Cx37 and Cx43, suggests that Cx37 channels serve a unique function in oogenesis. Female mice lacking Cx37 are sterile because oocytes do not complete their development. To test the hypothesis that the unique properties of Cx37 make it irreplaceable in oocytes, Cx43 was ectopically expressed in growing oocytes lacking Cx37. Transgenic mice were produced in which Gja1 is expressed in oocytes under control of the Zp3 (zona pellucida protein 3) gene promoter. When the transgene was crossed into the Cx37-null mutant line, oocyte–granulosa-cell coupling, oocyte growth and maturation, and fertility were all restored. Thus, despite their different properties, Cx43 is physiologically equivalent to Cx37 in coupling oocytes with granulosa cells.

WNTs are secreted extracellular signaling molecules that transduce their signals by binding to G protein-coupled receptors of the frizzled (FZD) family. They control diverse developmental processes, such as cell fate specification, cell proliferation, cell differentiation, and apoptosis. Although WNT signaling has been shown to be essential for development of the ovary, its mechanistic role in folliculogenesis within the adult ovary has not been studied extensively. Therefore, the objective of this study was to investigate the regulation and function of WNT2 signaling in mouse granulosa cells. Immunostaining identified WNT2 as being expressed in granulosa cells throughout folliculogenesis, but with varying signal strength: in sequential sections, WNT2 immunoreactivity was strongest in healthy antral follicles but weak in atretic follicles. Knockdown of WNT2 expression using transfected short interfering RNA decreased DNA synthesis in granulosa cells, whereas WNT2 overexpression using a recombinant viral vector enhanced it. WNT2 knockdown led to accumulation of glycogen synthase kinase-3beta (GSK3B) in the cytoplasm but reduced the expression of beta-catenin. Conversely, WNT2 overexpression reduced the expression of GSK3B in the cytoplasm and induced beta-catenin translocation from the membrane into the nucleus. Beta-catenin knockdown also inhibited DNA synthesis in granulosa cells and neutralized the effect of WNT2 overexpression. WNT2/beta-catenin signaling had a slight effect on the apoptosis of granulosa cells. Taken together, the data indicate that WNT2 regulates beta-catenin localization in granulosa cells, and WNT2/beta-catenin signaling contributes to regulating their proliferation.

SUMMARY The essential role of connexin43 (Cx43) during oogenesis has been demonstrated by the severe germ cell deficiency and arrested folliculogenesis observed in Cx43 knockout mice. Recently, another mutant mouse strain became available (Gja1Jrt/+) that carries the dominant loss-of-function Cx43 mutation, Cx43G60S. Gja1Jrt/+ mice display features of the human disease oculodentodigital dysplasia (ODDD), which is caused by mutations in the GJA1 gene. We used this new mutant strain to study how a disease-linked Cx43 mutant affects oogenesis. We found that female mutant mice are subfertile with significantly reduced mating success and small litters. The phosphorylated species of the Cx43 protein are reduced in the mutant ovaries in association with impaired trafficking and assembly of gap junctions in the membranes of granulosa cells, confirming that the mutant protein acts dominantly on its wild-type counterpart. Correspondingly, although starting with a normal abundance of germ cells, ovaries of the mutant mice contain significantly fewer pre-ovulatory follicles and do not respond to superovulation by gonadotropins, which is at least partially the result of reduced proliferation and increased apoptosis of granulosa cells. We conclude that the Gja1Jrt mutation has a dominant negative effect on Cx43 function in the ovary, rendering the females subfertile. Given these findings, closer examination of reproductive function in ODDD human females is warranted.

WNTs are extracellular signaling molecules that exert their actions through receptors of the frizzled (FZD) family. Previous work indicated that WNT2 regulates cell proliferation in mouse granulosa cells acting through CTNNB1 (beta-catenin), a key component in canonical WNT signaling. In other cells, WNT signaling has been shown to regulate expression of connexin43 (CX43), a gap junction protein, as well as gap junction assembly. Since previous work demonstrated that CX43 is also essential in ovarian follicle development, the objective of this study was to determine if WNT2 regulates CX43 expression and/or gap-junctional intercellular communication (GJIC) in granulosa cells. WNT2 knockdown via siRNA markedly reduced CX43 expression and GJIC. CX43 expression, the extent of CX43-containing gap junction membrane, and GJIC were also reduced by CTNNB1 transient knockdown. CTNNB1 is mainly localized to the membranes between granulosa cells but disappeared from this location after WNT2 knockdown. Furthermore, CTNNB1 knockdown interfered with the ability of follicle-stimulating hormone (FSH) to promote the mobilization of CX43 into gap junctions. We propose that the WNT2/CTNNB1 pathway regulates CX43 expression and GJIC in granulosa cells by modulating CTNNB1 stability and localization in adherens junctions, and that this is essential for FSH stimulation of GJIC.

We investigate the connection between the epoch of reionization and the present day universe, by examining the extended mass reionization histories of dark matter halos identified at z = 0. We combine an N-body dark matter simulation of a 600 Mpc volume with a three-dimensional, seminumerical reionization model. This provides reionization redshifts for each particle, which can then be connected with the properties of their halos at the present time. We find that the vast majority of present-day halos with masses larger than ∼ few ×10 11 M reionize earlier than the rest of the universe. We also find significant halo-to-halo diversity in mass reionization histories, and find that in realistic inhomogenous models, the material within a given halo is not expected to reionize at the same time. In particular, the scatter in reionization times within individual halos is typically larger than the scatter among halos. From our fiducial reionization model, we find that the typical 68% scatter in reionization times within halos is ∼ 115 Myr for 10 12±0.25 M halos, decreasing slightly to ∼ 95 Myr for 10 15±0.25 M halos. We find a mild correlation between reionization history and environment: halos with shorter reionization histories are typically in more clustered environments, with the strongest trend on a scale of ∼ 20 Mpc. Material in Milky Way mass halos with short reionization histories is preferentially reionized in relatively large HII regions, implying reionization mostly by sources external to the progenitors of the presentday halo. We investigate the impact on our results of varying the reionization model parameters, which span a range of reionization scenarios with varying timing and morphology.