Early Stages Of Embryogenesis Research Articles

Embryonic control of epidermal cell patterning in the root and hypocotyl of Arabidopsis.

A position-dependent pattern of epidermal cell types is produced during the development of the Arabidopsis seedling root and hypocotyl. To understand the origin and regulation of this patterning mechanism, we have examined the embryonic expression of the GLABRA2 (GL2) gene, which encodes a cell-type-specific transcription factor. Using in situ RNA hybridization and a sensitive GL2::GFP reporter, we discovered that a position-dependent pattern of GL2 expression is established within protodermal cells at the heart stage and is maintained throughout the remainder of embryogenesis. In addition, we show that an exceptional GL2 expression character and epidermal cell pattern arises during development of the root-hypocotyl junction, which represents an anatomical transition zone. Furthermore, we find that two of the genes regulating seedling epidermal patterning, TRANSPARENT TESTA GLABRA (TTG) and WEREWOLF (WER), also control the embryonic GL2 pattern, whereas the CAPRICE (CPC) and GL2 genes are not required to establish this pattern. These results indicate that position-dependent patterning of epidermal cell types begins at an early stage of embryogenesis, before formation of the apical meristems and shortly after the cellular anatomy of the protoderm and outer ground tissue layer is established. Thus, epidermal cell specification in the Arabidopsis seedling relies on the embryonic establishment of a patterning mechanism that is perpetuated postembryonically.

Regulation of the acute myeloid leukemia cell line OCI/AML-2 by endothelial nitric oxide synthase under the control of a vascular endothelial growth factor signaling system.

It is generally accepted that the vascular endothelial growth factor (VEGF) signal system has no role in the maintenance of normal blood cell formation, although it obviously regulates the development of primitive hematopoiesis during an early stage of embryogenesis. The VEGF signaling pathway, however, might have some role in malignant hematopoiesis, since malignant hematopoietic cells, including acute myeloid leukemia (AML) cells, have been shown to express VEGF and its receptors. In endothelial cells, the VEGF/Flk-1/KDR signal system is a very important generator of nitric oxide (NO) through the activation of its downstream effectors phosphatidylinositol-3-OH-kinase (PI3-K), Akt kinase and endothelial NO synthase (eNOS). It is known that NO regulates hematopoiesis and modulates AML cell growth. The role of the VEGF signaling pathway in the control of AML cell growth through eNOS, however, has not been studied. By using the OCI/AML-2 cell line, which expresses VEGF receptor-2, ie Flk-1/KDR, eNOS and VEGF, as analyzed by flow cytometry, and produces VEGF into growth medium, as analyzed by ELISA, we showed that the Akt kinase and NOS activities in these cells were decreased by the inhibitors of VEGF, Flk-1/KDR and PI3-K, and NOS activity also by the direct inhibitor of NOS. The decreased NOS activity led to inhibition of clonogenic cell growth and, to some extent, induction of apoptosis. We also found that blast cells of bone marrow samples randomly taken from 14 AML patients uniformly expressed Flk-1/KDR and to varying degrees eNOS and VEGF, as analyzed by immunohistochemistry. We conclude that autocrine VEGF through Flk-1/KDR, by activating eNOS to produce NO through PI3-K/Akt kinase, maintains clonogenic cell growth in the OCI/AML-2 cell line. Since the patient samples did not express VEGF in all cases, it is possible that in vivo the regulatory connection between these two signal systems is also mediated via endocrine VEGF in addition to autocrine or paracrine VEGF.

Le développement psychologique commence-t-il dès la première forme embryonnaire ?

Does psychological development begin as soon as conception has taken place? One must keep in mind the fluctuations of parenthood, especially in the pregant woman. Then, the present writer rises the question of the part played by conception in the psychological development. Some of the disorders of this development might be connected with events occurring in the early stages of embryogenesis. This paper examines three kinds of situation: 1. The « replacement child » (i. e. the child conceived voluntarily following the death of a preceding one); 2. The child conceived through rap or incest; 3. The «survivor» child. It is possible that psychological development has its roots in the pre-natal stage.

Regulation of the mRNAs Encoding Proteins of the BMP Signaling Pathway during the Maternal Stages of Xenopus Development

Activation of the Xenopus bone morphogenetic protein (BMP) pathway is coincident with the onset of zygotic transcription but requires maternal signaling proteins. The mechanisms controlling the translation of mRNAs that encode proteins of the BMP pathway were investigated by using polysome association as an assay for translational activity. Our results indicate that five different mRNAs encoding proteins of the BMP pathway were translationally regulated during Xenopus development. These mRNAs were either not associated or inefficiently associated with polysomes in oocytes, and each was recruited to polysomes at a different developmental stage. The Smad1 and ALK-2 mRNAs were recruited to polysomes during oocyte maturation, whereas the BMP-7 and XSTK9 mRNAs were recruited during the early stages of embryogenesis. The ALK-3 mRNA was not efficiently associated with polysomes during any maternal stage of development and was efficiently recruited to polysomes only after the onset of zygotic transcription. In general, for all stages except oocytes, polysome recruitment was associated with the presence of a 3′ poly(A) tail. However, there was not an obvious correlation between the absolute length of poly(A) and the efficiency of polysome recruitment, indicating that the relationship between poly(A) tail length and translation during early frog embryogenesis is complex. We further focused on the BMP-7 mRNA and demonstrated that sequence elements within the 3′UTR were necessary for recruitment of the BMP-7 mRNA to polysomes and sufficient to direct the addition of poly(A) and activate translation of a reporter during embryogenesis. Interestingly, the BMP-7 mRNA lacks the previously defined eCPE sequences proposed to direct poly(A) addition and translational activation during embryogenesis. The implications of our findings for translational regulation of maternal mRNAs during embryogenesis and for the activation of the BMP pathway are discussed.

A monoclonal antibody, MIN/3/60, that recognizes the sulpho-Lewis(x) and sulpho-Lewis(a) sequences detects a sub-population of epithelial glycans in the crypts of human colonic epithelium.

Monoclonal antibodies (MAbs) directed to Lewis(x) (Le(x)) and related carbohydrate sequences have been invaluable in anticipating biological roles for these oligosaccharides by detecting the remarkable changes that occur in their expression from the earliest stages of embryogenesis, through development and sequential stages of cell differentiation and maturation. A notable impact has been in the molecular dissection of ligand-receptor interactions in key cell adhesion events at the initial stages of leukocyte recruitment in inflammation, and almost certainly in the metastasis of epithelial tumours. Antibodies that recognise Le(x) and the 3'-sialyl forms were observed to identify leukocyte subsets; these were subsequently found to match those recognized by the leukocyte-endothelium adhesion molecules, the E- and P-selectins. We now describe a MAb (rat hybridoma MIN/3/60) raised to 3'-sulpho-Le(x), a carbohydrate sequence which, in vitro, is bound not only by the E-, L-, and P-selectins, but also by the cysteine-rich domain of the macrophage endocytosis receptor. We observe that MIN/3/60 is bispecific, however; it binds 3'-sulpho-Le(a) as well as 3'-sulpho-Le(x). Nevertheless, our exploratory studies reveal that it may be a useful histochemical reagent when used in conjunction with a monospecific antibody to 3'-sulpho-Le(a). The MIN/3/60 antibody reveals a sub-population of epithelial glycans in the crypts of Lieberkühn in normal human colon.

The expression of chicken NOV, a member of the CCN gene family, in early stage development

The nephroblastoma overexpressed gene, NOV, is a member of the CCN gene family. We investigated the NOV gene expression pattern in the chicken during early stage embryogenesis. Several embryonic structures showed a distinct expression pattern. The initial expression was detected in Hensen’s node (Hamburger and Hamilton stage (HH) 5). The expression was noted in the presumptive notochord and floor plate forming cells. The expression on the left side was more elongated posteriorly, a type of left–right asymmetry. Chicken NOV gene expression in the forming notochord and floor plate was observed until HH 18. The expression was also detected in the ventral area of the mesencephalon and isthmus at HH 14–16.

Nkx2.5 and Nkx2.6, homologs of Drosophila tinman, are required for development of the pharynx.

Nkx2.5 and Nkx2.6 are murine homologs of Drosophila tinman. Their genes are expressed in the ventral region of the pharynx at early stages of embryogenesis. However, no abnormalities in the pharynges of embryos with mutations in either Nkx2.5 or Nkx2.6 have been reported. To examine the function of Nkx2.5 and Nkx2.6 in the formation of the pharynx, we generated and analyzed Nkx2.5 and Nkx2.6 double-mutant mice. Interestingly, in the double-mutant embryos, the pharynx did not form properly. Pharyngeal endodermal cells were largely missing, and the mutant pharynx was markedly dilated. Moreover, we observed enhanced apoptosis and reduced proliferation in pharyngeal endodermal cells of the double-mutant embryos. These results demonstrated a critical role of the NK-2 homeobox genes in the differentiation, proliferation, and survival of pharyngeal endodermal cells. Furthermore, the development of the atrium was less advanced in the double-mutant embryos, indicating that these two genes are essential for both pharyngeal and cardiac development.

Morphology, ontogeny and functional anatomy of the seeds of Colophospermum mopane

Only one seed is carried inside the indehiscent fruit of Colophospermum mopane . Both the seed and fruit constitute the dispersal unit and the seed germinates while still inside the fruit. The mature seed of C. mopane has a thin seed coat that shows little differentiation, similar to the seed coats of typical Leguminous overgrown seeds. The malpighian cells that usually form a mechanical layer of protection are absent and this may be attributed to the seed being enclosed in an indehiscent fruit where the pericarp forms the protective layer. The thin, undifferentiated seed coat may also be an adaptation to low rainfall as it allows for the rapid uptake of water where rainfall occurs in small quantities or is of short duration. The seed originates from a bitegmic ovule. The inner layer of the inner integument persists throughout most of seed development and differentiates into an endothelium. The remainder of the inner integument degenerates completely at the time of fertilisation but the entire outer integument persists and differentiates into the seed coat. The integumentary cells display high mitotic activity in both the anticlinal and periclinal planes throughout seed ontogeny another feature reminiscent of overgrown or neotenous seeds. Up to the 5mm stage of the young seed, the older cell layers towards the outside of the integument are obliterated and resorbed as they are continually being replaced by new cell layers that originate from the inner layers. After the 5mm stage, the cells of the subepidermal layer begin to divide periclinally and anticlinally to keep pace with the inner layers. The senescent cells of the middle layer are then obliterated between the dividing cells of the inner integumentary layers and the subepidermal layers. The number of cell layers remains more or less constant throughout seed ontogeny because the obliteration of the older layers prevents the seed coat from becoming thick and multiplicative. The anticlinal divisions bring about the lateral extension of the seed coat to give rise to an aril that circumvents the seed. Another feature reminiscent of overgrown seeds is the convoluted appearance of the cotyledons which suggests that extensive seed growth is limited by the size of the fruit locule. As a consequence of the convoluted cotyledons the seeds may be regarded as ruminate. Rumination is, however, not only an outcome of seed growth inside the limited space of the fruit locule but also of uneven anticlinal divisions in the endothelium during early stages of embryogenesis. The entire vascular supply of the seed is limited to the aril and no secondary ramifications of vascular traces occur in the remainder of the seed coat. Due to extensive anticlinal divisions of the seed coat the primary vascular bundle is stretched in a lateral plane, causing the xylem strands to separate from the surrounding parenchyma cells, as well as from one another. This causes an air canal to develop in the primary vascular bundle that originates from the funiculus. The lateral extension of the aril also causes the position of cambiai-like meristematic areas that initially surround the primary vascular bundle to shift so that the area occupied by these cells becomes V-shaped or U-shaped. The cambial-like meristematic areas give rise to secondary vascular bundles. The micropyle is small and occluded with a dark staining substance that makes it impermeable to water. The integuments as well as the mature seed coat contain high concentrations of tanniniferous substances. The large seed size of the xerophytic C. mopane may be explained by its common origin from the ancestors of Guibourtia and Copaifera that occurred in high rainfall zones.

Non-invasive visualization of sperm mitochondria behavior in transgenic mice with introduced green fluorescent protein (GFP)

Using high sensitive polymerase chain reaction (PCR), we previously demonstrated that selective elimination of sperm mitochondrial DNA occurred during early embryogenesis in mouse. To analyze the process morphologically in more detail, a non-invasive, real-time observation of sperm mitochondria was used. Transgenic mice that express green fluorescent protein (GFP) exclusively in mitochondria (mtGFP-tg mice) were generated. The fluorescence in mtGFP-tg mice was strong and stable enough to carry out repeated observations under confocal laser scanning microscopy. In these mtGFP-tg mice it was revealed that the sperm mitochondria were selectively eliminated from egg cytoplasm during the two-cell stage of early embryogenesis. Therefore, mtGFP-tg mice should contribute to studies on sequential or repeated analysis of mitochondria.

Evidence for endoreduplication: germ cell DNA levels prior to chromatin diminution in Mesocyclops edax.

We studied the functional significance of marked differences in the DNA content of somatic cells and germ line nuclei by static Feulgen-DNA cytophotometry for several species of microcrustaceans that exhibit chromatin diminution during very early stages of embryogenesis. Mature females and males showed many gonadal nuclei with elevated amounts of DNA that persist until dispersal of this "extra" DNA throughout the cytoplasm as fragments and coalescing droplets of chromatin during anaphase of the diminution division.

Changes in cytokinin distribution in the ovule and ovary of Taraxacum officinale Web. in early stages of embryogenesis.

Quantitative changes in the hormonal status of the ovules and ovaries were first studied in Taraxacum officinale Web. at the early stages of embryogenesis. The plant material was analyzed by ELISA using labeled anti-rabbit antibodies. A new procedure for differential and quantitative determination of the main endogenous cytokinins based on the estimation of the effective zeatin and zeatin riboside concentrations from calibration curves constructed using zeatin and zeatin riboside as standard antigens was developed. It was shown that, at the three initial stages of embryogenesis examined, the concentration of zeatin uniformly increased in T. officinale ovules. The concentration of zeatin riboside, conversely, uniformly decreased. However, their total concentration changed insignificantly. A gradual increase in the concentration of the active and storage hormone forms from the ovary to the ovule was shown.

Mitochondrial DNA instability and peri-implantation lethality associated with targeted disruption of nuclear respiratory factor 1 in mice.

In vitro studies have implicated nuclear respiratory factor 1 (NRF-1) in the transcriptional expression of nuclear genes required for mitochondrial respiratory function, as well as for other fundamental cellular activities. We investigated here the in vivo function of NRF-1 in mammals by disrupting the gene in mice. A portion of the NRF-1 gene that encodes the nuclear localization signal and the DNA-binding and dimerization domains was replaced through homologous recombination by a beta-galactosidase-neomycin cassette. In the mutant allele, beta-galactosidase expression is under the control of the NRF-1 promoter. Embryos homozygous for NRF-1 disruption die between embryonic days 3.5 and 6.5. beta-Galactosidase staining was observed in growing oocytes and in 2. 5- and 3.5-day-old embryos, demonstrating that the NRF-1 gene is expressed during oogenesis and during early stages of embryogenesis. Moreover, the embryonic expression of NRF-1 did not result from maternal carryover. While most isolated wild-type and NRF-1(+/-) blastocysts can develop further in vitro, the NRF-1(-/-) blastocysts lack this ability despite their normal morphology. Interestingly, a fraction of the blastocysts from heterozygous matings had reduced staining intensity with rhodamine 123 and NRF-1(-/-) blastocysts had markedly reduced levels of mitochondrial DNA (mtDNA). The depletion of mtDNA did not coincide with nuclear DNA fragmentation, indicating that mtDNA loss was not associated with increased apoptosis. These results are consistent with a specific requirement for NRF-1 in the maintenance of mtDNA and respiratory chain function during early embryogenesis.

A family of IGF-II mRNA binding proteins (IMP) involved in RNA trafficking

During a search for trans -acting factors associating with insulin-like growth factor II (IGF-II) mRNAs, we recently identified a family of three I GF-II m RNA-binding P roteins (IMP1, IMP2 and IMP3) that exhibit multiple attachments to IGF-II leader 3 mRNA and the reciprocally imprinted H19 RNA. IMPs contain the unique combination of two RNA recognition motifs (RRMs) and four hnRNP K homology (KH) domains. IMP1 is orthologous to the chicken zipcode-binding protein (ZBP-1), and the mouse c-myc coding region determinant-binding protein (CRD-BP) that associates with g -actin and c-myc mRNA, respectively. Moreover, the p62 protein identified in hepatocellular carcinoma represents a splice variant of IMP2, and IMP3 is orthologous to the Xenopus Vegetal 1 RNA-binding protein (Vg1-RBP/Vera). IMPs are produced in a biphasic fashion - initially during the early stages of embryogenesis and subsequently later in development. IMPs and their orthologues are predominantly cytoplasmic and are implicated in the transport of their RNA targets towards the leading edge in somatic cells and to the vegetal pole in Xenopus oocytes, respectively. RNA localization is a conserved mechanism of polarizing genetic information in the establishment of asymmetries during both embryogenesis and adult life, enabling local protein synthesis at final destinations within the cell. The identification of developmentally expressed zipcode-binding proteins indicates that RNA trafficking participates in processes such as cell-growth and migration during embryogenesis.

Study of the transfer of foreign genes into mussel Mytilus Galloprovincialis Lam. eggs by spermatozoa

The possibility of transferring exogenous DNA into eggs by mussel Mytilus galloprovincialis Lam. sperms both with the use of certain methods of transfection and without them was studied. The efficacy of egg fertilization by sperms treated with foreign DNA and the development of larvae at early stages of embryogenesis were evaluated. Negative effects of the contact between mussel sperms and exogenous DNA on fertilization and subsequent development were noted. The proportion of developing larvae decreased with increasing DNA concentration and sperm exposure. Transfer of plasmids pCMVlacZ and pMTbGH into eggs was observed in group crosses. With the use of PCR, foreign DNA sequences were found in the larvae at the stage of veliger 48 h after fertilization. An intense signal was recorded after sperm electroporation in 10% DMSO.

The poplar bark storage protein gene (Bspa) promoter is responsive to photoperiod and nitrogen in transgenic poplar and active in floral tissues, immature seeds and germinating seeds of transgenic tobacco.

In Populus, seasonal nitrogen storage involves the accumulation of a 32 kDa bark storage protein (BSP) in the inner bark parenchyma and xylem rays. Poplar BSPs are encoded by a multigene family and one member, bspA, has been cloned and sequenced. The regulation of bspA was investigated by transforming either hybrid poplar or tobacco with a chimeric gene consisting of the 2.8 kb bspA promoter fused to the coding region of beta-glucuronidase (uidA). In transformed poplar, the bspA 2.8 kb promoter conferred both short-day (SD) and nitrogen (N) inducibility to GUS and activity was localized to the bark (primary and secondary phloem, and cortex) and xylem rays. Night-break treatments inhibited SD induction of GUS. Deletion of the 1.6 kb distal DNA sequences from the bspA promoter eliminated SD induction of GUS while some N induction was retained. These results indicate that although poplar BSP is encoded by a multigene family, transcriptional activation of bspA per se can account for bsp expression in bark and xylem rays in response to either SD or N treatment. These results also show that the elements responsible for SD or N induction are separable. Because of the long generation intervals associated with trees, the developmental regulation of bspA in flowers, developing seeds, and germinating seeds was investigated by transforming the 2.8 kb bspA-promoter::uidA chimeric gene into tobacco. The bspA promoter was active in developing tobacco floral tissues and in seeds during early stages of embryogenesis, decreased progressively during seed maturation and regained activity upon seed germination. Although seed storage proteins of poplar share some similarities to poplar BSP, the observed developmental expression patterns in tobacco are consistent with a role for bspA in vegetative rather than seed storage protein storage.

Composition of eggs in relation to embryonic development and female size in giant crabs [Pseudocarcinus gigas (Lamarck)

The size and composition of eggs from 22 giant crabs (Pseudocarcinus gigas) were monitored over 165 days to determine trends through embryogenesis. Egg composition was most stable during the early stages of embryogenesis so additional sampling (n=143) was conducted during this period to assess the effect of female size, sampling location (east and west Tasmania)and successive broods between moults, on egg composition. During embryogenesis, eggs increased in diameter and moisture content while organic dry mass declined. Total carotenoid and lipid content per egg did not change significantly, whereas protein declined (as ash-free dry mass per egg). This indicates that protein was used preferentially to lipid, which may be an adaptation to the deeper water habitat of P. gigas. Females with heavy and intermediate carapace wear were considered more likely to have produced previous clutches and they produced eggs with significantly less carotenoid. The eggs of larger females contained significantly more water, less protein and less carotenoid, whereas there was no effect on total lipid (P<0. 05). Although the effects of female size on egg composition were significant, the magnitude of the effect was small (highest for carotenoid, r2=0. 17). Consequently, it is unlikely that larval viability is affected, or that larger females contribute more to recruitment than predicted by fecundity.

A novel two-component hybrid molecule regulates vascular morphogenesis of the Arabidopsis root.

The developmental ontogeny of the vascular system (consisting of xylem, phloem and [pro]cambium) is poorly understood despite its central role in plant physiology. We show that in the Arabidopsis root meristem, xylem cell lineages are specified early, whereas phloem and procambium are established through a set of asymmetric cell divisions. These divisions require the WOODEN LEG (WOL) gene. The WOL gene encodes a novel two-component signal transducer with an unusual tandem arrangement of two receiver domains. It is expressed specifically in the vasculature from the early stages of embryogenesis on, consistent with a role as a sensor for vascular morphogenesis.

Molecular cloning of NADPH-cytochrome P450 oxidoreductase from silkworm eggs. Its involvement in 20-hydroxyecdysone biosynthesis during embryonic development.

Using RT-PCR, a cDNA fragment of NADPH-cytochrome P450 oxidoreductase from silkworm, Bombyx mori, was cloned from three-day-old nondiapause eggs. RACE was used to isolate the ends of the DNA. The full-length cDNA obtained was composed of 3471 bp with an open reading frame encoding a protein of 687 amino-acid residues with a relative molecular mass of 77 700. The protein, fused with glutathione S-transferase, was expressed in Escherichia coli and purified to homogeneity. The fused protein not only had NADPH-dependent cytochrome c-reducing activity, but also acted as an electron carrier from NADPH to bovine adrenal 21-hydroxylase P450 in the steroid hydroxylation reaction, confirming that the protein is the silkworm NADPH-cytochrome P450 oxidoreductase. Ecdysone 20-hydroxylase activity in the nondiapause egg microsomes increased until the fourth day after oviposition, and then decreased, little being detected on the ninth day. An antibody raised against the P450 reductase inhibited the ecdysone hydroxylation. Immunoblot analyses of the microsomes indicated that the P450 reductase protein appeared distinctly in the three-day-old nondiapause eggs and, in contrast to the developmental pattern of ecdysone hydroxylase activity, continued to increase as the embryos developed. These results suggest that ecdysone hydroxylation in the early stage of embryogenesis is dependent on the presence of both P450 reductase and ecdysone 20-hydroxylase P450, but its gradual reduction in the later stage may be due to the decrease in the level of ecdysone 20-hydroxylase P450.

Temporal and spatial expression of the cell-cycle regulator cul-1 in Drosophila and its stimulation by radiation-induced apoptosis.

Cul-1 protein is part of the ubiquitin ligase complex that is conserved from yeast to humans. This complex specifically marks cell-cycle regulators for their subsequent destruction. Two null mutations of the cul-1 gene are known, in budding yeast and in nematodes. Although in both these organisms the cul-1 gene executes essentially the same function, the manifestation of its lack-of-function mutations differs considerably. In yeast the mutation causes arrest at the G(1)/S-phase transition, whereas in nematodes excessive cell divisions occur because mutant cells are unable to exit the mitotic cycle. We isolated cul-1 orthologues from two model organisms, Drosophila melanogaster and mouse. We show that the Drosophila full-length cul-1 gene restores the yeast mutant's inability to pass through the G(1)/S-phase transition. We also characterize expression of this gene at the transcript and protein levels during Drosophila development and show that cul-1 gene is maternally supplied as a protein, but not as an RNA transcript. Zygotic transcription of the gene, however, resumes at early stages of embryogenesis. We also found an increase in cul-1 transcription in cultured cells treated with a lethal dose of gamma-irradiation.

Isolation and characterization of Xenopus laevis aldolase B cDNA and expression patterns of aldolase A, B and C genes in adult tissues, oocytes and embryos of Xenopus laevis

Following previous cloning and expression studies of Xenopus aldolase C (brain-type) and A (muscle-type) cDNAs, we cloned here two Xenopus aldolase B (liver-type) cDNAs (XALDB1 and XALDB2, 2447 and 1490 bp, respectively) using two different liver libraries. These cDNAs had very similar ORF with only one conservative amino acid substitution, but 3′-UTR of XALDB1 contained ca. 1 kb of unrelated reiterated sequence probably ligated during library construction as shown by genomic Southern blot analysis. In adult, aldolase B mRNA (ca. 1.8 kb) was expressed strongly in kidney, liver, stomach, intestine, moderately strongly in skin, and very weakly in all the other tissues including muscles and brain, which strongly express aldolase A and C mRNAs, respectively. In oocytes and early embryos, aldolase A and C mRNAs occurred abundantly as maternal mRNAs, but aldolase B mRNA occurred only at a residual level, and its strong expression started only after the late neurula stage, mainly in liver rudiment, pronephros, epidermis and proctodeum. Thus, active expression of the gene for aldolase B, involved in dietary fructose metabolism, starts only later during development (but before the feeding stage), albeit genes for aldolases A and C, involved in glycolysis, are expressed abundantly from early stages of embryogenesis, during which embryos develop depending on yolk as the only energy source.