Pigment cell organization in the hypodermis of zebrafish

Zebrafish have a characteristic horizontal-stripe pigment pattern made by a specific distribution of three types of pigment cells: melanophores, xanthophores, and iridophores. This pattern is a valuable model to investigate how the spatial patterns form during animal development. Although recent findings suggest that the interactions among the pigment cells play a key role, the particular details of these interactions have not yet been clarified. In this report, we performed transmission electron microscopic study to show the distribution, conformation, and how the cells contact with each other in the hypodermis. We found that the pigment cells form complex but ordered, layered structures in both stripe and interstripe regions. The order of the layered structures is kept strictly all through the hypodermal regions. Our study will provide basic information to investigate the mechanism of pigment pattern formation in zebrafish.

Fetal subcutaneous tissue thickness (SCTT) in healthy and gestational diabetic pregnancies

OBJECTIVE

To determine reference values of fetal subcutaneous tissue thickness (SCTT) throughout gestation in a healthy population and to compare them with those from a population of pregnant women with gestational diabetes under standard therapy.

METHODS

Three hundred and three women recruited from a high-risk pregnancy clinic were classified as being healthy (n = 218) or as having gestational diabetes (n = 85) on the basis of a negative or positive oral glucose tolerance test, respectively. They were enrolled into the cross-sectional study at 20 weeks' gestation. Ultrasound examinations were performed approximately every 3 weeks until delivery at term. The mid-arm fat mass and lean mass (MAFM, MALM), the mid-thigh fat mass and lean mass (MTFM, MTLM), the abdominal fat mass (AFM) and the subscapular fat mass (SSFM) were evaluated. Time-specific reference ranges were constructed from the 218 healthy women and a conventional Student's t-test was performed to compare SCTT values between the two study groups throughout gestation.

RESULTS

Normal ranges, including 5th, 50th and 95th centiles of the distribution, were generated for each SCTT parameter obtained in each of the two groups of women. Significant differences were found between the two study groups at 37-40 weeks' gestation for MTFM, at 20-22 and 26-28 weeks for MTLM, at 31-34 and 35-37 weeks for MAFM, at 26-28 and 38-40 weeks for SSFM, and at 39-40 weeks for AFM, the mean residual values always being greater in gestational diabetic women than they were in the group of healthy pregnant women.

CONCLUSIONS

We provide gestational age-specific reference values for fetal SCTT. Fetal fat mass values, particularly in late gestation, are greater in women with gestational diabetes compared with healthy women. The reference values may have a role in assessing the influence of maternal metabolic control on fetal state.

lin-35 Rb Acts in the Major Hypodermis to Oppose Ras-Mediated Vulval Induction in C. elegans

Specification of vulval precursor cell (VPC) fates in C. elegans has served as an important signal transduction paradigm. Genetic studies have indicated that a large group of synthetic multivulva (SynMuv) genes, including the Rb ortholog lin-35, antagonizes the activity of the EGF receptor-Ras-MAP kinase pathway during VPC specification. A prevalent view has been that Rb-mediated transcriptional regulation and chromatin remodeling activities act in the VPCs to antagonize Ras activation through effects on promoters of target genes of the EGF receptor-Ras-MAP kinase pathway that promote vulval fates. Here, we have investigated the cellular focus of lin-35 using conventional genetic mosaic analysis and tissue-specific expression. Our results indicate that lin-35 activity is required in the major hypodermal syncytium and not in the VPCs to inhibit vulval fates. LIN-35 Rb may inhibit vulval fates by regulating a signal from hyp7 to the VPCs or the physiological state of hyp7.

SMA-1 spectrin has essential roles in epithelial cell sheet morphogenesis in C. elegans

During Caenorhabditis elegans development, the embryo acquires its vermiform shape due to changes in the shape of epithelial cells, a process that requires an apically localized actin cytoskeleton. We show that SMA-1, an ortholog of beta(H)-spectrin required for normal morphogenesis, localizes to the apical membrane of epithelial cells when these cells are rapidly elongating. In spc-1 alpha-spectrin mutants, SMA-1 localizes to the apical membrane but its organization is altered, consistent with the hypothesis these proteins act together to form an apically localized spectrin-based membrane skeleton (SBMS). SMA-1 is required to maintain the association between actin and the apical membrane; sma-1 mutant embryos fail to elongate because actin, which provides the driving force for cell shape change, dissociates from the apical membrane skeleton during morphogenesis. Analysis of sma-1 expression constructs and mutant strains indicates SMA-1 maintains the association between actin and the apical membrane via interactions at its N-terminus and this activity is independent of alpha-spectrin. SMA-1 also preserves dynamic changes in the organization of the apical membrane skeleton. Taken together, our results show the SMA-1 SBMS plays a dynamic role in converting changes in actin organization into changes in epithelial cell shape during C. elegans embryogenesis.

Prenatal protein restriction does not affect the proliferation and differentiation of rat preadipocytes

Poor development in utero may favor the development of obesity in adulthood. Animal studies showed that embryo manipulation in vitro or nutritional insults during the embryonic and fetal stages of development may lead to obesity in adult life. We studied the in vitro proliferation and differentiation of adipocytes to investigate whether early protein restriction may program cell growth and development. In a series of experiments, 2 different low-protein diet protocols were compared. In both cases, pregnant rats were fed a diet with a high (18-20%) or low (8-9%) protein content during gestation and/or lactation. Preadipocytes were isolated from the fetuses, neonates, and weanling offspring. Moderate protein restriction, imposed during either gestation and/or lactation, did not affect the capacity of preadipose cells to divide or store fat. Because previous studies showed that early protein restriction alters the metabolism of sulfur amino acids, we also investigated the effects of methionine, taurine, and homocysteine on proliferation and differentiation of preadipocytes. The supplementation of the diet with methionine or the addition of homocysteine and taurine to the culture media did not influence the development of preadipocytes. We obtained no evidence for the direct reprogramming of the precursor or stem cells and suggest that the subsequent alteration in fat accretion may therefore reflect a change in the neuroendocrine environment.

Does a superficial musculoaponeurotic system exist in the face and neck? An anatomical study by the tissue plastination technique

An exact knowledge of the subcutaneous layers in the different regions of the face and neck is important in several surgical disciplines. In the parotid region, a superficial musculoaponeurotic system (SMAS) has been described. The existence of a SMAS as a guiding structure for the surgeon in the other regions of the face and neck has been discussed but is controversial. Therefore, the authors investigated the development of the subcutaneous connective-tissue layers in the different facial regions and in the neck. They studied these regions in 22 human fetuses using the technique of plastination histology and in three newborn and three adult specimens using sheet plastination. In addition, they dissected the neck and face in 10 fresh adult cadavers to identify the SMAS as in the surgical situation. The results show that no SMAS could be detected in any facial regions other than the parotid region. In the parotid region, it is thick and attached to the parotid sheath. However, it becomes very thin, discontinuous, and undissectable in the cheek area. No SMAS can be found in the neck, in which the authors are the first to describe a fascia covering both sides of the platysma. This fascia has close topographical connections to the subcutaneous layers of the adjoining regions. On the basis of these findings, the surgical pathways have to be defined regionally in the face. A "platysma fascia" can be considered as a surgical landmark in the neck. Therefore, the authors conclude that it is not justified to generalize a SMAS as a surgical guiding structure.

Caenorhabditis elegans T-box genes tbx-9 and tbx-8 are required for formation of hypodermis and body-wall muscle in embryogenesis

Transcription factors containing the DNA binding motif, T-box, play an important role in the embryonic development of metazoans. There are 20 T-box genes in the nematode Caenorhabditis elegans, three of which reportedly have postembryonic functions. We characterized two T-box genes, tbx-9 and tbx-8, that are phylogenetically related to each other. tbx-9 is expressed in a subset of embryonic cells that are precursors of the intestine, body-wall muscle, and hypodermis. The expression pattern of tbx-8 is markedly similar to that of tbx-9. Both tbx-9 mutants and tbx-8 mutants show incomplete penetrant morphogenetic defects in embryogenesis, but the malformations of the tbx-9 and tbx-8 mutants are observed in different parts of their bodies. In embryos with both tbx-9 and tbx-8 inactivated, the body structure is severely disorganized, more so than the sum of the separate mutant phenotypes. Further analysis shows that the hypodermis and body-wall muscle show abnormalities at the site of morphogenetic defects of these mutants. Together, these data indicate that tbx-9 and tbx-8 do not only contribute individually to formation of the hypodermis and body-wall muscle, but also suggests functional redundancy between tbx-9 and tbx-8 in embryonic morphogenesis.

C. elegans NIMA-related kinases NEKL-2 and NEKL-3 are required for the completion of molting

Caenorhabditis elegans molting is a process during which the apical extracellular matrix of the epidermis, the cuticle, is remodeled through a process of degradation and re-synthesis. Using a genetic approach, we identified nekl-3 as essential for the completion of molting. NEKL-3 is highly similar to the mammalian NEK kinase family members NEK6 and NEK7. Animals homozygous for a hypomorphic mutation in nekl-3, sv3, had a novel molting defect in which the central body region, but not the head or tail, was unable to shed the old cuticle. In contrast, a null mutation in nekl-3, gk506, led to complete enclosure within the old cuticle. nekl-2, which is most similar to mammalian NEK8, was also essential for molting. Mosaic analyses demonstrated that NEKL-2 and NEKL-3 were specifically required within the large epidermal syncytium, hyp7, to facilitate molting. Consistent with this, NEKL-2 and NEKL-3 were expressed at the apical surface of hyp7 where they localized to small spheres or tubular structures. Inhibition of nekl-2, but not nekl-3, led to the mislocalization of LRP-1/megalin, a cell surface receptor for low-density lipoprotein (LDL)-binding proteins. In addition, nekl-2 inhibition led to the mislocalization of several other endosome-associated proteins. Notably, LRP-1 acts within hyp7 to facilitate completion of molting, suggesting at least one mechanism by which NEKL-2 may influence molting. Notably, our studies failed to reveal a requirement for NEKL-2 or NEKL-3 in cell division, a function reported for several mammalian NEKs including NEK6 and NEK7. Our findings provide the first genetic and in vivo evidence for a role of NEK family members in endocytosis, which may be evolutionarily conserved.

Caenorhabditis elegans WASP-interacting protein homologue WIP-1 is involved in morphogenesis through maintenance of WSP-1 protein levels

Mammalian WASP and N-WASP are involved in reorganization of the actin cytoskeleton through activation of the Arp2/3 complex and in regulation of cell motility or cell shape changes. In the present study, we identified WASP-interacting protein homologue (WIP)-1 in Caenorhabditis elegans. WIP-1 contains the domains and sequences conserved among mammalian WIP family proteins. Yeast two-hybrid analysis detected a physical interaction between WIP-1 and WSP-1, the sole homologue of WASP/N-WASP in C. elegans. Western analysis of embryo lysates showed that RNA interference (RNAi) treatment for wip-1 decreased levels of WSP-1 protein, and wsp-1(RNAi) treatment decreased levels of WIP-1 protein. However, wsp-1 mRNA levels were not decreased in wip-1(RNAi)-treated embryos, and wip-1 mRNA levels were not decreased in wsp-1(RNAi)-treated embryos. Furthermore, disruption of WIP-1 by RNAi resulted in embryonic lethality with morphologic defects in hypodermal cell migration, a process known as ventral enclosure. This phenotype was similar to that observed in RNAi experiments for wsp-1. Immunostaining showed that WIP-1 was expressed by migrating hypodermal cells, as was WSP-1. This expression during ventral enclosure was reduced in wip-1(RNAi)-treated embryos and wsp-1(RNAi)-treated embryos. Our results suggest that C. elegans WIP-1 may function in hypodermal cell migration during ventral enclosure by maintaining levels of WSP-1.

The hedgehog-related gene wrt-5 is essential for hypodermal development in Caenorhabditis elegans

The Caenorhabditis elegans genome encodes a series of hedgehog-related genes, which are thought to have evolved and diverged from an ancestral Hh gene. They are classified into several families based on their N-terminal domains. Here, we analyze the expression and function of a member of the warthog gene family, wrt-5, that lacks the Hint/Hog domain. wrt-5 is expressed in seam cells, the pharynx, pharyngeal-intestinal valve cells, neurons, neuronal support cells, the excretory cell, and the reproductive system. WRT-5 protein is secreted into the extracellular space during embryogenesis. Furthermore, during larval development, WRT-5 protein is secreted into the pharyngeal lumen and the pharyngeal expression changes in a cyclical manner in phase with the molting cycle. Deletion mutations in wrt-5 cause embryonic lethality, which are temperature sensitive and more severe at 15 degrees C than at 25 degrees C. Animals that hatch exhibit variable abnormal morphology, for example, bagging worms, blistering, molting defects, or Roller phenotypes. We examined hypodermal cell junctions using the AJM-1Colon, two colonsGFP marker in the wrt-5 mutant background and observed cell boundary abnormalities in the arrested embryos. AJM-1Colon, two colonsGFP protein is also misplaced in pharyngeal muscle cells in the absence of WRT-5. In conclusion, we show that wrt-5 is an essential gene that - despite its lack of a Hint domain - has multiple functions in C. elegans and is implicated in cell shape integrity.

M142.2 (cut-6), a novel Caenorhabditis elegans matrix gene important for dauer body shape

The cuticle of the nematode Caenorhabditis elegans is a collagenous extracellular matrix which forms the exoskeleton and defines the shape of the worm. We have characterized the C. elegans gene M142.2, and we show that this is a developmentally regulated gene important for cuticle structure. Transgenic worms expressing M142.2 promoter fused to green fluorescent protein showed that M142.2 is expressed in late embryos and L2d predauers, in the hypodermal cells which synthesize the cuticle. The same temporal pattern was seen by RT-PCR using RNA purified from specific developmental stages. A recombinant fragment of M142.2 was expressed in Escherichia coli and used to raise an antiserum. Immunohistochemistry using the antiserum localized M142.2 to the periphery of the alae of L1 and dauers, forming two longitudinal ribbons over the hypodermal cells. Loss-of-function of M142.2 by RNAi resulted in a novel phenotype: dumpy dauers which lacked alae. M142.2 therefore plays a major role in the assembly of the alae and the morphology of the dauer cuticle; because of its similarity to the other cut genes of the cuticle, we have named the gene cut-6.

mig-5/Dsh controls cell fate determination and cell migration in C. elegans

Cell fate determination and cell migration are two essential events in the development of an organism. We identify mig-5, a Dishevelled family member, as a gene that regulates several cell fate decisions and cell migrations that are important during C. elegans embryonic and larval development. In offspring from mig-5 mutants, cell migrations are defective during hypodermal morphogenesis, QL neuroblast migration, and the gonad arm migration led by the distal tip cells (DTCs). In addition to abnormal migration, DTC fate is affected, resulting in either an absent or an extra DTC. The cell fates of the anchor cell in hermaphrodites and the linker cells in the male gonad are also defective, often resulting in the cells adopting the fates of their sister lineage. Moreover, 2 degrees vulval precursor cells occasionally adopt the 3 degrees vulval cell fate, resulting in a deformed vulva, and the P12 hypodermal precursor often differentiates into a second P11 cell. These defects demonstrate that MIG-5 is essential in determining proper cell fate and cell migration throughout C. elegans development.

Neuronal migration is regulated by endogenous RNAi and chromatin-binding factor ZFP-1/AF10 in Caenorhabditis elegans

Endogenous short RNAs and the conserved plant homeodomain (PHD) zinc-finger protein ZFP-1/AF10 regulate overlapping sets of genes in Caenorhabditis elegans, which suggests that they control common biological pathways. We have shown recently that the RNAi factor RDE-4 and ZFP-1 negatively modulate transcription of the insulin/PI3 signaling-dependent kinase PDK-1 to promote C. elegans fitness. Moreover, we have demonstrated that the insulin/IGF-1-PI3K-signaling pathway regulates the activity of the DAF-16/FOXO transcription factor in the hypodermis to nonautonomously promote the anterior migrations of the hermaphrodite-specific neurons (HSNs) during embryogenesis of C. elegans. In this study, we implicate the PHD-containing isoform of ZFP-1 and endogenous RNAi in the regulation of HSN migration. ZFP-1 affects HSN migration in part through its negative effect on pdk-1 transcription and modulation of downstream DAF-16 activity. We also identify a novel role for ZFP-1 and RNAi pathway components, including RDE-4, in the regulation of HSN migration in parallel with DAF-16. Therefore, the coordinated activities of DAF-16, ZFP-1, and endogenous RNAi contribute to gene regulation during development to ensure proper neuronal positioning.

The mesorectum: hypothesis on its evolution

BACKGROUND

Two points are controversial in the anatomy of the mesorectum: (1) its origin; and (2) the existence of the lateral ligaments. We studied these structures in animals and in human fetuses.

METHODS

Dissections were performed on quadrupedal mammals (29 dogs and 32 pigs) and 28 primates (Macaca apes). Moreover, macroslices of Macaca ape and of 182 human fetuses were examined histologically.

RESULTS

In quadrupedal mammals, we found no traces of any adipose masses comparable to the human mesorectum nor were there ligaments of suspension. In the ape, the adipose tissue in the mesosigmoid forms an adipose cuff that completely surrounds the extraperitoneal rectum. Two dense connective bands were found between the lateral wall of the pelvis and the perirectal tissue. Both the mesorectum and the lateral ligaments were clearly identified in the sections of human fetus only at the end of the fifth month but not earlier.

CONCLUSIONS

On the basis of our analysis of 3 animal species, we conclude that the mesorectum and lateral ligaments are absent in quadrupedal mammals but are present in primates. Therefore, we hypothesize that these structures appeared with the attainment of the upright position, even though other hypotheses are possible.

Fetal anterior wall thickness and amniotic fluid insulin levels: an interdependence?

PURPOSE

Excessive fetal fat as the hallmark of GDM pregnancy complications is one consequence of fetal hyperinsulinism. Noninvasive methods for fetal surveillance and measurement of fetal fat are needed. The purpose of this study was to test the hypothesis that measurements of the fetal anterior abdominal wall thickness (AAWT) in women with GDM will allow early detection of fetal hyperinsulinism.

MATERIALS AND METHODS

Amniocentesis was performed between 28 and 32 weeks of gestation (wks) in 220 women with GDM (diagnosed by 75 g oGTT at 24 to 28 wks). Amniotic fluid insulin levels (AFIL) were determined by a commercially available radioimmunoassay. Transabdominal ultrasound provided fetal biometric measurements following standard procedures and the AAWT including fetal skin and subcutaneous tissue at the time of amniocentesis. Maternal parameters (weight, BMI, oGTT blood glucose levels and mean daily blood glucose levels) were correlated with fetal biometric data and with AFIL.

RESULTS

There was no difference in AAWT in women with GDM and no correlation with mean AFIL. AFIL also did not correlate with any other fetal measurement or with mean oGTT blood glucose levels. AFIL only showed a correlation with maternal weight (p = 0.02) and maternal BMI (p = 0.01). The correlation was present for values both before pregnancy and at the time of amniocentesis.

CONCLUSION

In the early third trimester, AAWT measurements do not correlate with fetal insulin levels.

Cytochemical study of in situ differentiation of white adipose cells in rat

AIM

The aim of the present study was to follow up the histochemical and enzyme-histochemical characteristics of differentiating white adipose cells of rat in situ.

METHOD

Nine rat fetuses aged 15-21 day of gestation were used. Fragments from the subcutaneous tissue of lower limb were frozen at -18 degrees C. On consecutive cryostat sections Sudan III-hematoxylin staining and enzyme-histochemical reactions for NADH2-cytochrome C-reductase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and lipoprotein lipase were performed.

RESULTS

The onset of the rat adipocyte differentiation was detected at days 15-16 of gestation. It was seen as appearance and accumulation of lipid droplets, rounding of the cells and displacement of the nuclei to the cell periphery. Gradually, with the advance of gestational age the number of differentiating adipose cells increased and lipid packages, composed of mature-like unilocular adipocytes and multilocular adipocytes that had not yet completed their differentiation, were formed. The differentiating embryonal adipose cells expressed positive enzyme-histochemical reactions for NADH2-cytochrome C-reductase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and lipoprotein lipase.

CONCLUSION

The described histochemical and enzyme-histochemical characteristics could be used as markers for distinguishing the earliest embryonal adipose cells in rat, which is impossible with the classic histological techniques. At the same time they might be accepted as the primary morphological criteria of adipocyte differentiation in situ.

Cytochemical and immunohistochemical evidence of direct origin of white adipocytes from mesenchymal cells

AIM

By using histochemical, enzymohistochemical and immunohistochemical methods the present study aims to find out specific morphological markers in the precursors of the white subcutaneous adipocytes of human and rat embryos, which could be used for identification and help in clarification of the origin of that cell type.

MATERIAL AND METHODS

On cryostat sections of subcutaneous tissue from the thigh region of human embryos and hind limb of rat embryos histological hematoxylineosin staining, Sudan III-hematoxylin staining and enzyme-histochemical reactions for lipoprotein lipase are performed. On paraffin section of the same material immunohistochemical reaction for leptin is performed.

RESULTS

The analysis reveals that the earliest preadipocytes possess specific histochemical, enzymohistochemical and immunohistochemical features, which characterize exclusively these cells but not the fibroblasts and endothelial cells scattered around in the subcutaneous tissue. These features include lipid drops, positive enzymohistochemical reaction for lipoprotein lipase and immunohistochemical expression for leptin.

CONCLUSION

The results could be used as evidence of direct origin of the white adipocytes from the embryonal mesenchyme through their own progenitor cells rather than through fibroblasts or endothelial cells.