Morphological study of surgically induced open neural tube defects in chick embryos--postoperative 24 hours

Feedback between tissue packing and neurogenesis in the zebrafish neural tube

Balancing the rate of differentiation and proliferation in developing tissues is essential to produce organs of robust size and composition. Although many molecular regulators have been established, how these connect to physical and geometrical aspects of tissue architecture is poorly understood. Here, using high-resolution timelapse imaging, we find that changes to cell geometry associated with dense tissue packing play a significant role in regulating differentiation rate in the zebrafish neural tube. Specifically, progenitors that are displaced away from the apical surface due to crowding, tend to differentiate in a Notch-dependent manner. Using simulations we show that interplay between progenitor density, cell shape and changes in differentiation rate could naturally result in negative-feedback control on progenitor cell number. Given these results, we suggest a model whereby differentiation rate is regulated by density dependent effects on cell geometry to: (1) correct variability in cell number; and (2) balance the rates of proliferation and differentiation over development to 'fill' the available space.

Experimental models of spinal open neural tube defect and Chiari type II malformation

INTRODUCTION

Experimental animal models are essential for investigation of the pathoembryogenesis, pathophysiology, and management strategy of spinal open neural tube defect (ONTD) and its associated anomalies including Chiari type II malformation. Genetic, chemical/nutrient, and surgical models have been widely used for a variety of purposes. The aim of this article is to review the representative animal models of spinal ONTD and associated Chiari type II malformation with respect to their advantages and disadvantages.

DISCUSSION

Among them, the surgical model was described in detail because it is familiar to neurosurgeons and it is used for evaluations of prenatal repair of spinal ONTDs. The surgical model also has advantages because it allows quantitative analysis of the lesions. A description of our previous studies on spinal ONTDs using a chick surgical model is presented as an example.

Effects of Levetiracetam on neural tube development and closure of the chick embryos in ovo

PURPOSE

Effects of Levetiracetam (LEV) within its therapeutic range at a 50 mg/kg dose for the chick embryo in ovo has been studied in order to demonstrate whether LEV would effect neural tube closure at the macroscopic morphology or LEV administered embryos still encounter neuroglial detrimental effects at the histological level.

METHODS

Embryos were randomly seperated into control (n = 20) and study (n = 20) groups. The eggshell was windowed at specifically 24 h of incubation, and area underlying the membrane was excised to allow injection with 4.5 μl LEV in the study group, while physiologic saline (0.045 ml) were injected in the control group and each egg were re-incubated for 48 h more. Then, histological and immunohistochemical evaluation of the subjects were done.

RESULTS

Macroscopic evaluation revealed immaturity of the placental vessel network in number and width for the study group in comparison to the controls. Defects of migration, decrease in the crista neuralis content, delay of the basal plates structures in the formation of the usual configuration, and delay in the cellular proliferation and the delay of development for the central nervous system were determined in the LEV-exposed group. Immunostaining of S100 proteins in this study has clearly demonstrated increased expression patterns of both neuroglial and neuronal cell populations. Toluidine blue stainings revealed mostly bipolar, differentiating neurons and crista neuralis cells which is concordant with active migration and differentiation.

CONCLUSIONS

LEV found that delay in the closure of the neural tube and microcephalic fetuses disturb further morphological, biochemical, and functional development.

Reclosure of surgically induced spinal open neural tube defects by the intraamniotic injection of human embryonic stem cells in chick embryos 24 hours after lesion induction

OBJECT

The authors previously reported that human embryonic stem cells (hESCs) injected into the amniotic cavity of chick embryos immediately after neural tube incision in a surgically induced spinal open neural tube defect (ONTD) model promote the reclosure capacity of neural tubes. To simulate more closely the clinical situation of human ONTDs, in which a substantial time period elapses before the prenatal diagnosis of spinal ONTDs, the authors investigated whether this reclosure capacity remains enhanced by the intraamniotic injection of hESCs at 24 hours after ONTD induction.

METHODS

One hundred twenty-two chick embryos with ONTDs were randomly assigned to two groups: the control group (59 embryos) and the hESC-injection group (hESC group, 63 embryos). After the neural tubes of both groups had been opened, the hESC group underwent direct intraamniotic injection with hESCs marked with an enhanced green fluorescent protein at 24 hours after ONTD induction. The lengths of the remnant ONTDs were measured and the presence of hESCs was determined at 4, 6, and 8 days after ONTD induction. No difference in survival rates was observed between the two groups. The mean length of the ONTDs, adjusted for body length at the time of death and initial lesion length, was significantly shorter in the hESC group than in the control group (p < 0.001). No hESCs were found within reclosed neural tubes; rather, they covered the defect area during the reclosure process.

CONCLUSIONS

The authors demonstrate that hESCs injected into the amniotic cavity at 24 hours after ONTD induction enhance reclosure ability in chick embryos.

Enhancement of re-closure capacity by the intra-amniotic injection of human embryonic stem cells in surgically induced spinal open neural tube defects in chick embryos

To evaluate the re-closure promoting capacity of human embryonic stem (hES) cells injected into the amniotic cavity on spinal open neural tube defects (ONTDs) of chick embryos, neural tubes were opened at Hamburger and Hamilton stage 18 or 19 and the embryos were divided into three groups: a control group (no injection), a vehicle group, and a hES cell group (injection of 20,000 hES cells immediately after neural tube incision). On postoperative days 3, 5, and 7, ONTDs were significantly more re-closed in the hES cell group than in the other two groups. hES cells were present at the area in the process of re-closure, and covered ONTDs, but were not found in the re-closed area, suggesting indirect effects rather than cell replacement on the neural tissue.

Skin graft on the surgically induced spinal open neural tube defects does not induce lipomatous malformation but enhances re-closure to the normal state in chick embryos

To determine the effect of skin allograft on open neural tube defects (ONTDs), the neural tube was incised open using Hamburger and Hamilton stage 18 or 19 chick embryos for a length of six somites. Embryos were divided into two groups: graft and control (with and without skin allograft). On postoperative day 5, closure of ONTDs was more frequent in the graft group than in the control group (9/15 versus 0/15), and healing was nearly complete. However, typical lipomatous features were not observed. These results suggest that simple mechanical attachment of skin allograft on ONTDs does not lead to lipomatous malformation in chick embryos. On the other hand, our results support a potential role of skin allograft in the management of prenatal spinal ONTDs.

Is the re-closure of surgically induced open neural tube defect the repetition of primary neurulation? An experimental study with chick embryos

It is well known that surgically induced open neural tube defects (ONTDs) tend to re-close in early embryonic stages. To investigate whether the process of re-closure is a repetition of primary neurulation, the morphological changes of surgically induced ONTDs were chronologically examined in early chick embryos. Longitudinal incisions of 3-somite length were made in the neural tubes of chick embryos at Hamburger and Hamilton stage 18 or 19. About half of the embryos showed complete closure of the skin on surgical microscopic examination. The re-closed neural tubes showed no remarkable differences from the controls on histological examination. The process of re-closure involved a zipper-like (ventral to dorsal) closure in the transverse sections of neural tubes. The results indicate that the re-closure of surgically induced ONTDs does not repeat the process of natural primary neurulation.

Chronological changes of re-closure capacity in surgically induced spinal open neural tube defects of chick embryos

To investigate the re-closure capacity of surgically induced spinal open neural tube defects (ONTD) and its correlation to the cell proliferation activity in embryonic stages, longitudinal incisions of 3- or 6-somite lengths were made in neural tubes of chick embryos at Hamburger and Hamilton stage 18-19, and the length of the ONTDs was measured on postoperative days 2, 3, 5, 7, and 10. The results demonstrated that re-closure occurred more actively when the incision length was shorter. The chronological changes in the re-closure capacity of the ONTDs paralleled the proliferative activity of the neural tube. We conclude that surgically induced spinal ONTDs may be remodeled in early chick embryos and that manipulation of cell dynamics can enhance the re-closure process in the embryonic spinal cord tissue.

Cell kinetics of surgically induced spinal open neural tube defect in chick embryos

In an attempt to understand cell kinetics of open neural tube defects (ONTDs) in the embryonic stages, chronological changes of cell proliferation and cell death patterns in the surgically induced spinal ONTDs of chick embryos were investigated using proliferating cell nuclear antigen (PCNA) staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) method. ONTDs were induced at Hamburger and Hamilton stages 17-19. Compared with the control group, the surgery group showed a lower PCNA labeling index for 5 days after surgery and demonstrated more TUNEL-positive cells at 6 h, 3 and 5 days after surgery. Decreased cell proliferation and enhanced apoptosis were seen in the ventral as well as in the dorsal spinal cord. These results partly explain the functional deficits of ONTDs.

Morphological study of surgically induced open neural tube defect in old (14 and 21 days) chick embryos

As an experimental model for the research of open neural tube defect (NTD), the surgical model has several advantages over others, in spite of the fact that the pathogenetic mechanism is not compatible with the human intrauterine events. To make reproducible NTDs by surgery and to compare the surgically induced lesions with the human myeloschisis morphologically, we opened the neural tube for a length of 9-11 somites in Hamburger and Hamilton stage 16-19 chick embryos. Embryos which survived until the late in ovo life (total age 14 and 21 days) showed relatively reproducible open NTDs. Morphologically they are similar to human myeloschisis. This study suggests that the surgical model can be suitable for studies of open NTDs.