The effect of serum on in vitro maturation, in vitro fertilization and steroidogenesis of bovine oocytes co-cultured with granulosa cells

The influence of fetal calf serum alone (FCS) or associated with proestrous (FCS+PCS), estrous (FCS+ECS) or metaestrous (FCS+MCS) cow serum added to the culture medium and of the steroids produced by co-cultured granulosa cells were evaluated in terms of the in vitro maturation (IVM) and fertilization (IVF) of bovine oocytes. Supplementation of the medium with FCS+ECS and FCS+MCS resulted in higher proportions of oocytes that reached metaphase II (96.0% and 93.3%, respectively) and in higher proportions of embryos that reached the four- and eight-cell/morula stages (51.9% and 65.6%, respectively), whereas the supplementation with FCS and FCS+PCS resulted in only 79.2% and 67.5%, respectively, of matured oocytes and 26.7% and 34.3%, respectively, of cleaved embryos. These findings show that the best IVM and IVF were obtained at lower concentrations of estradiol produced by co-cultured granulosa cells (supplementation with FCS+ECS: 10.3 ng/ml and FCS+MCS: 2.1 ng/ml), whereas the worst results in IVM and IVF occurred at higher concentrations of estradiol that were obtained with FCS (33.1 ng/ml) and FCS+PCS (19.9 ng/ml) supplementation. These data suggest an inhibitory effect of estradiol on resumption of oocyte meiosis in vitro.

FORSE-1: a positionally regulated epitope in the developing rat central nervous system

We designed a protocol to identify cell surface molecules expressed in restricted spatial patterns in the developing central nervous system (CNS) that might be regulated by regionally restricted transcription factors. The immunogen was a membrane fraction from NT2/D1 embryocarcinoma cells that were induced to differentiate into neurons and upregulate Hox gene expression in response to retinoic acid. One monoclonal antibody (mAb), FORSE-1, specifically labels the rostral rat CNS from the earliest stages. Staining is observed in the rostral but not caudal neural folds of the embryo prior to neural tube closure. Staining is enriched in the forebrain as compared to the rest of the CNS, until E18. Between E11.5 and E13.5, only certain areas of the telencephalon and diencephalon are labeled. Later, up to E17.5, FORSE-1 labeling is specifically restricted to the telencephalon, where a correlation with mitotic activity is apparent: the ventricular zone labels with FORSE-1, while the cortical plate is negative. The staining of the neuroepithelium is intensified by acetone fixation, which also reveals, between E11.5 and E13.5, a dorsoventrally restricted, FORSE-1-positive region of the spinal cord. After E18, the entire CNS is labeled, through adulthood. The mAb labels the surfaces of dissociated, living cells. Other, non-CNS areas of FORSE-1 labeling are nasal and otic placodes, nasal epithelium, nasal glands, and early (E9.5-10.5) endoderm. mAb FORSE-1 recognizes an epitope present on both a high-molecular-weight (> 200 kDa) proteoglycan from embryonic and early postnatal brain, and on a 80 kDa doublet that is restricted to the CNS in the adult. These findings suggest the FORSE-1 antigen as a candidate cell surface molecule for mediating regional specification from the earliest stages of CNS development.

CD44 is expressed throughout pre-implantation human embryo development

The cell surface glycoprotein CD44 has been demonstrated in a variety of cell types in embryonic and adult tissues. We have established that CD44 is present on human oocytes, cumulus cells, early embryos and pre-hatched blastocysts by indirect immunofluorescence. We have also shown that CD44 is present on 8-11 week placental stroma cells, but not on the trophoblast. These findings demonstrate that CD44 is present throughout preimplantation development, and that down-regulation occurs on the embryonic surface after implantation.

Expression of vascular endothelial growth factor and its receptors in human renal ontogenesis and in adult kidney

Vascular endothelial growth factor (VEGF) may modulate vascular permeability, chemotaxis for monocytes, and protease activity. In addition, VEGF may play a role in embryonic and tumor angiogenesis. In fetal mouse kidney, VEGF mRNA and protein expression have been demonstrated. This finding led to the hypothesis that VEGF might be involved in renal growth and development. To further elucidate the role of VEGF in human kidney, expression of VEGF and its receptors, the specific tyrosine kinase receptors, fit-1 and KDR, were studied. In fetal (6-24 gestational wk; mesonephros and metanephros) and adult kidney, VEGF mRNA and protein could be colocalized in glomerular epithelia and collecting duct cells by in situ hybridization and immunohistology. By reverse transcription-polymerase chain reaction, mRNA of three VEGF isoforms, VEGF121, VEGF165, and VEGF189, were found in fetal kidney and cortex, isolated glomeruli, and medulla of adult human kidney. KDR and flt-1 mRNA were coexpressed in endothelia of glomeruli and in peritubular capillaries in fetal and adult kidney. These data support the assumption that VEGF and its receptors may influence renal ontogenesis. We speculate that the constitutive expression of VEGF in adult kidney may be required for the function of VEGF receptor positive-fenestrated endothelia in glomeruli and postglomerular vessels. The expression of VEGF in collecting duct and of its receptors in medullary capillaries may in addition be relevant for maintaining medullary osmolality.

Enhanced results in mouse and human embryo culture using a modified human tubal fluid medium lacking glucose and phosphate

PURPOSE

Because various recent studies in both human and laboratory animals have indicated an influential role of glucose and phosphate in embryonic development, this study was initiated to assess the effect of culture medium lacking glucose and phosphate on human IVF.

RESULTS

Initial studies with mouse zygotes indicated a significant improvement in embryonic development in both a F1 hybrid and a random-bred "two-cell block" strain, using a modified HTF medium which contained EDTA and glutamine (Gln) and also with a similar medium which lacked glucose and phosphate. Subsequently, a prospective randomized trial of human IVF has begun in which infertile patients are sequentially assigned to have IVF using one of three media. The three media are regular HTF, HTF containing EDTA and Gln (referred to as Basal HTF), and HTF with EDTA and Gln but devoid of glucose and phosphate ions (referred to as Basal XI HTF).

CONCLUSIONS

Initial results indicate that Basal XI HTF medium, a modified form of HTF containing EDTA and glutamine but devoid of glucose and phosphate, greatly improves the in vitro development of mouse and human embryos over HTF and Basal HTF medium.

Dermatoglyphics, fetal growth, and insulin dependent diabetes in children under 5 years

Examination of dermatoglyphic patterns in 112 diabetic children under 5 years and matched controls found no difference between the groups. Either those developing diabetes under 5 do not experience the same genetic and environmental conditions that influence its development in later life or the dermatoglyphic abnormalities described in later onset insulin dependent diabetes mellitus reflect the vast number of pattern formations available for study, which has inevitably led to some statistically significant associations.

In vitro and in vivo survival of cryopreserved sheep embryos

Experiments were conducted to devise an efficient method to cryopreserve ovine embryos for field application. Embryos were surgically collected from superovulated ewes on Day 6 after natural breeding; oocytes were collected from ovaries obtained at the abattoir. Osmotic behavior of oocytes and embryos was determined by measuring their responses to hypertonic solutions of CsCl or sucrose. Embryos and oocytes contracted osmotically by decreasing their volumes proportionally to the reciprocal of the solution's osmolality. The respective nonosmotic volumes of embryos in CsCl and sucrose were 13.8 and 13.5% of their isotonic volume, and those of oocytes were 18.5 and 19.6%. Tests of the permeability of morulae to commonly used cryoprotectants, ethylene glycol (EG), propylene glycol (PG), dimethyl sulfoxide (DMSO), and glycerol (Glyc), showed that the order of permeability was EG > PG > DMSO approximately Glyc. Comparison of the efficacy of cryoprotective agents indicated that the respective survivals of embryos frozen in EG, PG, and DMSO were 76.9, 62.5, and 55.6%, based on their development into hatched blastocysts in vitro. Therefore, EG appeared to be superior to the other two cryoprotectants for freezing sheep embryos. To determine the functional survival of embryos in vivo, 67 embryos frozen in EG were thawed and directly diluted with phosphate-buffered saline; 47 of these (70%) appeared morphologically normal and were transferred into 14 recipients. Five of these recipients, which had received a total of 16 embryos, became pregnant. Ten lambs were born, showing that the method employed in this study for cryopreservation of sheep embryos followed by their direct dilution out of EG has potential application for practical field use.

Regionalization of the developing forebrain: a comparison of FORSE-1, Dlx-2, and BF-1

The FORSE-1 monoclonal antibody (mAb) was generated using a strategy designed to produce mAbs against neuronal cell surface antigens that might be regulated by regionally restricted transcription factors in the developing CNS. To determine whether FORSE-1 has a labeling pattern similar to that of known transcription factors, the expression of BF-1 and Dlx-2 was examined by in situ hybridization on sections serial to those labeled with FORSE-1. We find a striking overlap between BF-1 and FORSE-1 in the telencephalon; both are expressed in the lateral but not the medial walls of the telencephalon, and the boundaries of expression are apparently identical. FORSE-1 staining is detected prior to BF-1 expression in the neural tube, however. FORSE-1 and Dlx-2 have very different patterns of expression in the forebrain, suggesting that regulation by Dlx-2 cannot by itself explain the distribution of FORSE-1. However, they share some sharp boundaries in the diencephalon. In addition, FORSE-1 identifies some previously unknown boundaries in the developing forebrain. These results indicate that a new cell surface marker can be used to subdivide the embryonic telencephalon and diencephalon into regions smaller than previously described, providing necessary complexity to the developmental patterning in the forebrain.

Lineage tracing demonstrates that blastomeres of early cleavage-stage human pre-embryos contribute to both trophectoderm and inner cell mass

We injected a fluorescent lineage tracer (Texas Red-lysine-dextran) into individual blastomeres of donated human diploid 2- to 8-cell pre-embryos and cultured them to blastocysts. Once pre-embryos reached the expanded blastocyst stage, they were fixed and examined in a scanning confocal microscope to identify the location of fluorescent tracer. In successfully injected pre-embryos that developed to expanded blastocysts, we found that randomly injected blastomeres formed both trophectoderm (TE) and inner cell mass (ICM). More labelled progeny were found in TE than in ICM. Our results show that individual early blastomeres are not yet committed to form either TE or ICM but instead can form both rudiments.

ATP content of human oocytes and developmental potential and outcome after in-vitro fertilization and embryo transfer

The relationship between the ATP content of mature human oocytes and developmental potential after uterine transfer of sibling embryos was examined in 20 non-male factor in-vitro fertilization (IVF) patients matched for age, fertility history, ovarian stimulation protocol, oocyte quality and number, stage and morphology of embryos at uterine transfer. ATP content was determined for uninseminated and unfertilized oocytes for each cohort, and for embryos that developed after dispermic fertilization or which showed significant fragmentation. The effect of reduced ATP content on meiotic maturation, fertilization and preimplantation development was examined in cultured mouse oocytes treated with uncouplers of mitochondrial oxidative phosphorylation. The results demonstrated that meiotic maturation occurs in both mouse and human oocytes over a wide range of ATP contents, and that the ATP content of normal-appearing, metaphase II human oocytes can differ significantly between cohorts; however, a higher potential for continued embryogenesis and implantation in the human is associated with embryos that develop from cohorts of oocytes with ATP contents > or = 2 pmol/oocyte. The findings are discussed with respect to possible aetiologies and developmental consequences for embryonic development of different oocyte ATP contents, and the extent to which mitochondrial function may determine or influence the continued developmental capacity of embryos which appear normal and developmentally viable at the early cleavage stages.

Are babies of normal birth weight who fail to reach their growth potential as diagnosed by ultrasound at increased risk?

The objectives of this study were to identify, by means of two third-trimester scans, fetuses with ultrasound evidence of inadequate growth but who were born with birth weights above the 10th centile for gestational age; and to determine if these infants constitute a high-risk group by comparing the incidence of obstetric intervention, of intrapartum complications and of neonatal morbidity between this group and the group of infants who showed no ultrasound evidence of intrauterine growth restraint. A total of 285 women with singleton pregnancies who were referred for a third-trimester ultrasound examination were included in this prospective study. Fetal weight was estimated by ultrasound twice in the third trimester and at each examination was assigned a centile score. A fall of > 20 centiles was taken as evidence of inadequate growth. The outcomes measured were the incidence of abnormal umbilical artery Doppler, induction of labor, meconiumstaining of the liquor, intrapartum fetal blood sampling, operative vaginal delivery, Cesarean section, Apgar score of < 7 at 5 min and admission to the neonatal intensive care unit. Seventy-five patients showed a drop of > 20 centiles between the first and second scans. The incidence of admission to the neonatal intensive care unit was greater in those infants who had ultrasound evidence of growth restraint. We conclude that infants of normal birth weight with inadequate growth diagnosed on ultrasound are not at increased risk, they have an increased incidence of admission to the neonatal intensive care unit, and they are more commonly found in mothers with diabetes mellitus.

Absence of the blood-clotting regulator thrombomodulin causes embryonic lethality in mice before development of a functional cardiovascular system

We have targeted the murine thrombomodulin (TM) gene in embryonic stem cells and generated embryos as well as mice with TM deficiency. The heterozygous TM-deficient (TM+/-) mice as compared to wild-type (TM+/+) littermates exhibit 50% reductions in the levels of TM mRNA and TM protein. However, TM+/- mice appear normal and are free of thrombotic complications. The homozygous TM-deficient (TM-/-) embryos die before embryonic day 9.5. An overall retardation in growth and development of TM-/- embryos is first evident on embryonic day 8.5 (8-12 somite pairs). However, no specific pathologic abnormalities are observed. These initial changes take place at a time when TM is normally expressed in the parietal yolk sac. The removal of embryonic day 7.5 TM-/- embryos from maternal decidua and their subsequent culture in vitro allow development to proceed to stages not observed in vivo (13-20 somite pairs) with the appearance of normal blood vessels in the visceral yolk sac and embryo. The results of our studies suggest that the failure of TM-/- embryos to survive at mid-gestation is a consequence of dysfunctional maternal-embryonic interactions caused by the absence of TM in the parietal yolk sac and demonstrate that the receptor is necessary for normal embryonic development in utero.

A targeted mutation in the mouse E-cadherin gene results in defective preimplantation development

The Ca(2+)-dependent cell adhesion molecule E-cadherin functions in the establishment and maintenance of epithelial cell morphology during embryogenesis and adulthood. Downregulation or complete shut-down of E-cadherin expression and mutation of the gene are observed during the progression of tumors of epithelial origin (carcinomas) and correlate with the metastatic potential. We have introduced a targeted mutation into the E-cadherin gene by homologous recombination in mouse embryonic stem cells. The mutation removes E-cadherin sequences essential for Ca2+ binding and for adhesive function. These embryonic stem cells were used to generate mice carrying the mutation. Heterozygous mutant animals appear normal and are fertile. However, the homozygous mutation is not compatible with life: E-cadherin -/- embryos show severe abnormalities before implantation. Particularly, the adhesive cells of the morula dissociate shortly after compaction has occurred, and their morphological polarization is then destroyed. Interestingly, the blastomers are still able to form desmosomes and tight junctions at sites of distorted cell-cell contact. Thus, maternal E-cadherin suffices for initial compaction of the morula but not for further preimplantation development to occur.

Emergence of multipotent hemopoietic cells in the yolk sac and paraaortic splanchnopleura in mouse embryos, beginning at 8.5 days postcoitus

We show by an in vitro approach that multipotent hemopoietic cells can be detected in the body of the mouse embryo between the stages of 10-25 somites (8.5-9.5 days of gestation)--i.e., prior to liver colonization (28-32 pairs of somites). Interestingly, hemopoietic cells appear in parallel in this location, the paraaortic splanchnopleura, and in the yolk sac, where they represent a new generation by reference to the primitive hemopoietic stem cells. Lymphoid cell clones, which could differentiate into mature B cells, were obtained from yolk sac and paraaortic splanchnopleura cell preparations but not from other tissues of the embryonic body. These B-cell precursors were first detected around the stage of 10 somites; thereafter, their initial minute numbers increased in parallel in the yolk sac and the paraaortic splanchnopleura, suggesting that their emergence in the two sites was simultaneous. By single cell manipulation, we show that these precursors can generate B and T lymphocytes and myeloid cells; these precursors can thus be defined as multipotent hemopoietic cells.

Expression of NADPH-diaphorase in the rat forebrain during development

Expression of NADPH-diaphorase (NADPH-d) was studied in the rat telencephalon and diencephalon from embryonic day 15 (E15) to postnatal day 30 (P30). The study has focused on the first appearance of NADPH-d staining in some areas which show high expression during adult life. The time of appearance ranged from E15 to the first days following birth, depending on the location of the cells. In many regions, neuronal processes, when staining appeared, were observed in close relationship with cerebral vessels. A possible role for nitric oxide in brain development should be explored.

Primary structure and developmental expression of Fbn-1, the mouse fibrillin gene

Previous studies have reported > 10 kilobases of human fibrillin-1 cDNA sequence, but a consensus regarding the 5' end of the transcript remains to be worked out. One approach to developing a clear consensus would be to search for regions of evolutionary conservation in transcripts from a related species such as mouse. As reported here, the mouse fibrillin-1 transcript encodes a highly conserved polypeptide of 2,871 amino acids. The upstream sequence that flanks the ATG is considerably less well conserved, however. Indeed, the ATG codon (which occurs in the context of a Kozak consensus sequence and is located just upstream of a consensus signal peptide) signals the point where human and mouse fibrillin-1 sequences cease to be nearly identical. Together, these results are consistent with previous efforts by Pereira et al. (Pereira, L., D'Alessio, M., Ramirez, F., Lynch, J. R., Sykes, B., Pangilinan, T., and Bonadio, J. (1993) Human Mol. Genet. 2, 961-968) to identify the human fibrillin-1 translational start site. Sequences immediately upstream of the ATG are GC-rich and devoid of TATA and CCAAT boxes, which suggests that the mouse fibrillin-1 gene will be broadly expressed. A survey of expression in mouse embryo tissues is consistent with this hypothesis and suggests two novel functions for fibrillin-associated microfibrils in non-elastic connective tissues.

P450c11B3 mRNA, transcribed from a third P450c11 gene, is expressed in a tissue-specific, developmentally, and hormonally regulated fashion in the rodent adrenal and encodes a protein with both 11-hydroxylase and 18-hydroxylase activities

The rat genome contains four P450c11 genes. One of these (CYP11B1) encodes P450c11 beta, which is the steroid 11 beta-hydroxylase found solely in the adrenal zona fasciculata/reticularis, and is responsible for the conversion of 11-deoxycorticosterone to corticosterone. A second P450c11 gene (CYP11B2) encodes P450c11AS, which is the aldosterone synthase found solely in the adrenal zona glomerulosa. P450c11AS has three activities, 11 beta-hydroxylase, 18-hydroxylase, and 18-oxidase, and is responsible for the conversion of 11-deoxycorticosterone to aldosterone. Recently, two more rat P450c11 genes, P450c11B3 and P450c11B4, were cloned. P450c11B4 appears to be a pseudogene, as two exons are replaced by unrelated DNA. P450c11B3 closely resembles P450c11 beta in mRNA and encoded amino acid sequences, predicting a protein of 498 amino acids. However, the expression of this mRNA and protein have not been demonstrated to date. We now demonstrate that this P450c11B3 mRNA is expressed in the adrenal gland several days after birth and is not expressed during fetal development or in the adult rat adrenal. Like P450c11 beta mRNA, P450c11B3 mRNA is expressed in the zona fasciculata/reticularis and not in the zona glomerulosa. However, the regulation of P450c11B3 mRNA expression is different from that of P450c11 beta mRNA, in that its abundance is decreased by ACTH in a sex-dependent fashion. Transfection of eukaryotic cells with a vector expressing P450c11B3 shows that this form of P450c11 can convert 11-deoxycorticosterone (DOC) to corticosterone and thus has the same enzymatic activity as P450c11 beta. In addition, P450c11B3 can convert DOC to 18-OH DOC and corticosterone to 18-OH corticosterone and thus has 18-hydroxylase activity similar to P450c11AS, but it lacks detectable 18-oxidase activity. Thus, P450c11B3 catalyzes 11 beta- and 18-hydroxylation and thus has a spectrum of activities midway between P450c11 beta and P450c11AS.

The thymosin beta 4 gene is strongly activated in neural tissues during early postimplantation mouse development

We studied the temporal and spatial distribution of the mRNA encoding for thymosin beta 4 (T beta 4), a small acidic actin-sequestering peptide, during the early postimplantation mouse development. Analysis of total embryo RNA demonstrated a strong activation of T beta 4 gene after gastrulation and coincident with neurulation. In situ hybridization showed that T beta 4 mRNA was strongly expressed in the central nervous system and peripheral ganglia, paralleling the gradient of neuronal differentiation. An intense signal was also observed in intraventricular macrophages and blood vessels. The role of T beta 4 in mammalian neuroembryogenesis is discussed.

The Pope and the ontogeny of persons

In his recent book Crossing the Threshold of Hope, Pope John Paul II airs his views on human reproduction. The pity is that he ignores most of modern genetics and embryology.

Involvement of the Sonic hedgehog gene in chick feather formation

To elucidate the molecular mechanisms of chick feather formation, we observed expression patterns of the Sonic hedgehog (Shh) gene, which is one of the vertebrate homologs of the Drosophila segment polarity gene, hedgehog, and encodes a signaling molecule functioning in limb pattern formation and motor neuron induction. We found that the Shh gene is also expressed in the apical region of the feather placodes and then in nine to eleven longitudinal stripes along feather filaments. The stripe was found to correspond to one of the outer marginal zones of each barb ridge, termed the zone of Shh expression. No significant expression signal was detected in the scale bud of developing legs. Thus, Shh is likely to function as an epithelial signaling molecule in epithelio-mesenchymal interaction during feather formation. Furthermore, since genes of bone morphogenetic protein-2 (BMP-2) and fibroblast growth factor-4 (FGF-4) are coexpressed with Shh during feather formation as observed in limb morphogenesis, interactions among FGF-4, Shh and BMP-2 may be involved in formation of feather filaments and barbs in a similar fashion as elucidated in limb pattern formation.

Developmental expression of transforming growth factor-alpha in the upper digestive tract and pancreas of the rat

This study was designed to examine the developmental expression and the localization of the transforming growth factor alpha (TGF-alpha) in the upper gastrointestinal tract and pancreas of the rat. Immunohistochemical techniques using an antibody against rat TGF-alpha were performed on the stomach, duodenum and pancreas of fetuses (19 to 21 days of gestation), of pups during the suckling period (days 0 to 13 postpartum) and after weaning (day 25 postpartum) and of adults. The temporal appearance of TGF alpha varied depending on the tissues. In the antral mucosa it likely appeared before 19 days of gestation. In this tissue, the immunostaining was intense from 20 days of gestation and did not decline after birth. In the duodenum, the TGF alpha immunoreactivity was definitely present with a high intensity at 20 days of gestation in villi, crypts and Brünner's glands and there after became irregular. In the fundic mucosa, TGF alpha expression was weak but clearly-established at 21 days of gestation, at least in parietal cells, and regularly increased after birth. In the pancreas, it appeared only after birth and solely in the exocrine gland. The TGF alpha immunoreactivity displayed as age progressed, first a granular pattern apparently confined in the supranuclear, i.e., Golgi area, then a diffuse cytoplasmic pattern. These findings suggest that TGF alpha may have a functional role during the developmental process of the digestive system.

Site-specific recombination of a transgene in fertilized eggs by transient expression of Cre recombinase

An efficient method of transgene modulation in fertilized eggs has been developed that uses the Cre/loxP recombination system. Twelve transgenic mouse lines carrying a chicken beta-actin promoter-loxP-chloramphenicol acetyltransferase (CAT) gene-loxP-beta-galactosidase gene construct were produced. After selection of the line showing the highest expression of the CAT gene in a variety of tissues, eggs of this line were injected in the male or female pronucleus with a Cre expression vector placed under the control of the chicken beta-actin promoter and kept in a circular form to avoid genomic integration. This resulted in a transient expression of Cre in the eggs, leading to recombination of the transgene as detected by galactosidase expression and DNA analysis. Recombination was completed before the morula stage with both types of pronuclear injections and occurred with a very high frequency; no mosaicism, no incomplete recombination, and no integration of the Cre sequence were observed in 18 mice born with this modified transgene. The beta-galactosidase gene was expressed in various tissues at levels comparable to those found for the CAT gene in the founder line. This Cre transient expression system should be useful for breeding transgenic lines in which transgene expression leads to sterility or lethality--in particular, for selecting transgenic lines with high expression of a potentially lethal transgene whose full activity is difficult to explore in a conventional transgenic system because of the risk of selecting for transgenic lines carrying only poorly expressed transgenes.

Morphology of vomeronasal organ cultures from fetal rat

The vomeronasal organs (VNOs) of rats were cultured from embryonic 15-day littermates on collagen-coated membrane in Dulbecco's modified Eagle's medium containing serum. The explants were observed sequentially and fixed at 4, 6, 8, 10 and 14 days in vitro (DIV). Organogenesis of VNOs and cell differentiation took place in vitro. Patterns of organogenesis of the VNO in vitro were different from those in vivo. Both sensory and supporting cells in the sensory epithelium had microvilli on their surface. Epithelial cells in aggregates of non-sensory epithelial cells had cilia and microvilli on their surface. Vomeronasal axons forming two to three large fascicles were seen originating from the VNO at 4, 6, and 8 DIV, and degenerated at 10 or 14 DIV. Glial cells (ensheathing cells) were observed in the fascicles. These morphological characteristics of VNO cells in vitro were similar to those observed in vivo.

Gap junctions in the developing nervous system

Cell-cell interactions are important in the development of the nervous system. Gap junctions (GJs) form direct intercellular channels that permit diffusion of ions and small molecules and thus cells linked by GJs can influence each other's properties or behavior either through transmission of electrical signals or through transfer of signaling molecules. In the developing nervous system, widespread GJ communication occurs at the time of neural induction, but in the adult nervous system it is much more restricted. In addition, certain events in neural development appear to involve the formation of transient junctional connections. This review examines briefly four aspects of neural development in which GJs may be involved, namely, neurulation, regional differentiation, migration, and axon guidance.