A lack of vitamin A on embryonic form of the major organ systems, the impact of construction
【Key Words】,,,,, vitamin
Influence of vitamin A deficiency on morphogenesis of main organ systems in embryo developing SONG Cui, LI Ting-yu
(Children's Hospital of Chongqing Medical University, Chongqing 400014, China)
Vitamin A (Vitamin A, VA) is a class derived from β
purple fragrant ketone derivatives, including retinol, retinaldehyde, retinoic acid and retinol esters. In which
retinoic acid (Retinoic acid, RA) is the most active derivative of VA. In normal embryonic development, the participation in the regulation of specific developmental events. As early as 30 years in the 19th century, there are studies show that in the embryonic development period,
pregnancy, maternal VA lacks (Vitamin A Deficiency, VAD) can affect the normal growth and development of offspring, or even result in offspring of various organs, the system congenital malformations. With the development of molecular biology and
the retinoic acid nuclear receptors in-depth study of people
from the gene level to the VA's role in embryonic development have a better understanding of [1,2]. This paper on the domestic and foreign scholars in recent years, the impact on
the VAD embryo form the major organ systems, and related mechanisms to build research are reviewed.
A retinoic acid nuclear receptors in embryonic development
Embryonic development in accordance with a certain space-
time model. VA derivatives of RA is essential for the normal development of embryos. VA primarily through two types of RA-
mediated retinoic acid nuclear receptors: RARs (retinoic acid receptors) and RXRs (retinoid X receptors), these two types of ligand-dependent transcription factor, regulating the
expression of target genes, thereby affecting the development of embryos. RARs and RXRs belong to the nuclear receptor
superfamily, have α, β, γ three kinds of subtypes, each
with subtypes encoded by different genes. Studies have found that retinoic acid nuclear receptor mutations in mice have occurred due to the abnormal and abnormal is very similar to
VAD, suggesting that VA on embryonic development of some of the effects produced by the nuclear retinoic acid receptor-
mediated achieved .
2 VA to the embryonic form of the major organ systems, the impact of construction
2.1 VA to build pattern in embryonic heart
The cardiovascular system is differentiated from the Sino-germ layers, first is the original formation of the cardiovascular system, on this basis, through growth, mergers, new, and shrinkage alterations gradual improvement process. VA
signal pathway in embryonic development has a very important role. Particular form of building in the heart of the process, the need to rely on RXR-α signaling pathway to regulate the
VA. RXR-α mutations can be induced myocardial thinning, or
even result in embryonic death. Merki et al , respectively epicardial and endocardial a series of tissue-specific RXR-α
mutation and found that RXR-α in mind the expression of
membrane form of construction for the normal heart is necessary. Also found that the performance of coronary artery anomalies-type and RXR-α deficiency related.
RA can occur related to the heart by regulating the expression of genes involved in embryonic form the heart of
building. The developing cardiovascular system express TbX1,
the genotype and phenotype of cardiac development are closely linked. Exogenous RA can not only cut TbX1, can also be through direct or indirect way to change the space TbX1 manifestations, which led to abnormal cardiac morphology, expressed as ventricular smaller outflow tract stenosis and atrial expanded, eventually caused an invalid loop or cycle termination of .
In addition to TbX1, the side plate mesoderm NKx2.5 and HAND1 key gene expression also affected by the regulation of
RA. Collop et al  will toad embryos observed after treatment with the RAR antagonist, in the heart of the formation of RA role in the process. Found in the heart of the early formation, RA can alter NKx2.5 and HAND1 expression, suggesting that side in the early mesoderm formation, at least to some extent by the regulation of RA. At the same time, the study found healing from the heart of the heart tube board needs to RA signals during boot. RA signals in mind only the healing of the heart tube plate in the process of a very
narrow time window to play a role, and its role in a dose-
dependent manner: high doses of RAR antagonist on both sides of myocardial wall can not be fusion; moderate doses of myocardial wall on both sides of blend, but the heart tube can
not form; low doses, the heart tube can be formed, but the heart of all of the partitions can not be completed. With the RA antagonist treatment, and their cardiac phenotype in the early stages of the formation of the performance of the heart similar to that of less mature myocardial cells. The above research suggests, RA signaling pathway through the RAR response element of the role took place during the formation for the toad heart is essential for the establishment of forms.
2.2 VA Morphology and Embryology of the nervous system to build
Nervous System originated in the neural ectoderm. Human embryonic 3rd weekend, the ectoderm ectodermal thickening between the notochord induce the formation of neural plate, neural plate formation of neural groove in central subsidence,
uplift of the edge of neural groove both sides of the neural crest. The formation of neural crest is the neural groove, the neural plate of columnar cells and normal cells in each ectodermal cell migration at cable .Neural crest in the
neural groove the middle of healing, the last before the formation of nerves in the first end of the hole and nerve holes. 4 weeks, complete closure of neural groove to neural tube. Human embryo the first 4 weeks, the first end of the
neural tube develop into the brain swelling, and the rest develop into the spinal cord. VA in the vertebrate embryo nervous system growth, differentiation, development and morphology has an important role in building .
Hindbrain during brain development is the transition
structure of the nervous system of the RA is the most sensitive region. White et al  found that VAD of the SD rats in pregnancy, 12.5d, embryonic development of the nervous system abnormalities appear visible to the naked eye, the most
obvious flaws in the hindbrain area, expressed as a large number of posterior cranial nerve (?, ?, ?, ? ) and the
posterior pharyngeal arch missing, foam ear swelling of ectopic and pre-primary vein. Shows the process of embryo formation need to participate in the tail of the hindbrain RA and related structures.
RA in different stages of embryonic development of the nervous system can play a role. Halilagic, etc.  to quail as a model study found that, in the early period of Corpus
Christi, VAD embryos the ventral neuroectodermal cell death increased, but the development of normal neural crest, to a later stage, the head mesenchymal and neural ectoderm ventral in a large number of apoptosis, the results of VAD embryos only reduced the formation of a single bulb and telencephalon between abnormal brain, and eventually died; in the early gastrulation, RA, including germ layers play a role in the development front, adjust the notochord the front surface of the endoderm to the neuroectodermal induction; in nerve-hole
closed when the RA involved in craniofacial morphology need to build signal transduction, including the amount of nasal prominence of interstitial formation and forebrain formation.
In recent years, the researchers set out to build form of
RA involved in the nervous system mechanism. Novitch et al  studies have shown that embryonic ventral spinal cord nerve cell apoptosis by the homology domain (home domain, HD) of regulation. Formed fibroblast growth factor (Fibroblast
Growth Factor, Fgfs) could inhibit the expression of HD proteins. The study found that Fgfs signal to escape the ventral spinal cord nerves can start to build the form. The type of vitamin A (Retinoid) can also be induced by spinal cord ventral nerve morphology build. Another study found that the tail of embryonic mesoderm arising from Fgfs inhibit neuronal differentiation, in neural differentiation and a reduced level of pre-Fgfs. The paraxial mesoderm of endogenous RA generated by down Fgfs, start to build neural
differentiation and neural patterns. Tips RA through the coordinating role and Fgfs embryonic body axis in the extended period, the promotion of neural differentiation [12,13]. Reposted elsewhere in the paper for free download http://