Aortic carboxypeptidase-like protein is expressed in collagen-rich tissues during mouse embryonic development

Aortic carboxypeptidase-like protein (ACLP) was originally identified in vascular smooth muscle cells and contains discoidin and catalytically inactive metallocarboxypeptidase domains. ACLP is a secreted protein that associates with the extracellular matrix and is essential for abdominal wall development and contributes to dermal wound healing. Because of these developmental and adult phenotypes, we examined the expression of ACLP by immunohistochemistry throughout mouse embryonic development. ACLP was not detected in 7.5 days post-coitum (dpc) embryos, however at 9.5 dpc low levels of expression were detected in the somites and dorsal aorta. Expression was detected in both the yolk sac and embryonic vasculature at 10.5d pc. ACLP expression increased in both large and small blood vessels at 11.5 and 13.5 dpc and intense expression was detected within the vascular smooth muscle layer in 16.5 dpc embryos. At later developmental time points, discrete areas of ACLP expression were detected in the mesenchymal cells in the dermal layer, developing skeletal structures, connective tissue, and in the umbilical ring and vessels. The predominance of ACLP immunoreactivity localized with collagen-rich regions including tendons and basement membranes. Overall, the developmental expression pattern is consistent with a regulatory or structural role in the abdominal wall, vasculature, and dermis.     

Expression of the transcription factor Zfp191 during embryonic development in the mouse

The human zinc finger protein 191 (ZNF191) is a Krüppel-like protein and can specifically interact with the widespread TCAT motif which constitutes the HUMTH01 microsatellite in the tyrosine hydroxylase (TH) gene (encoding the rate-limiting enzyme in the synthesis of catecholamines). Allelic variations of HUMTH01 are known to have a quantitative silencing effect on TH gene expression and to correlate with quantitative and qualitative changes in the binding by ZNF191. This factor has been isolated from bone marrow and promyelocytic leukemia cell lines indicating that ZNF191 also plays a role in hematopoiesis. Thus, ZNF191 could participate in the regulation of several genes implicated in different functions. Moreover, mice that are deficient in Zfp191, the murine homologue of ZNF191, have been shown to be severely retarded in development and to die approximately at embryonic day 7.5. In order to gain further insight into its biological functions, we have analysed the localisation of Zfp191 throughout mouse development. Expression was detected early during embryogenesis in ectodermal, endodermal, mesodermal and extra-embryonic tissues. In particular, Zfp191 was observed in the developing central nervous system. Interestingly, its expression levels were prominent in areas of proliferation such as the subventricular zone. Zfp191 expression pattern during development can account for the phenotypic features of Zfp191(-/-) embryos.     

Chondromodulin-I and tenomodulin are differentially expressed in the avascular mesenchyme during mouse and chick development

Chondromodulin-I (ChM-I) and tenomodulin (TeM) are homologous angiogenesis inhibitors. We have analyzed the spatial relationships between capillary networks and the localization of these molecules during mouse and chick development. ChM-I and TeM proteins have been localized to the PECAM-1-negative avascular region: ChM-I is expressed in the avascular cartilage, whereas TeM is detectable in dense connective tissues, including tendons and ligaments. We have also examined the vasculature of chick embryos by injection with India ink and have performed in situ hybridization of the ChM-I and TeM genes. The onset of ChM-I expression is associated with chondrogenesis during mouse embryonic development. ChM-I expression is also detectable in precartilaginous or noncartilaginous avascular mesenchyme in chick embryos, including the somite, sclerotome, and heart. Hence, the expression domains of ChM-I and TeM during vertebrate development incorporate the typical avascular regions of the mesenchymal tissues. This study was partly supported by Grants-in-Aid from the Ministry of Education, Culture, Sport, Science, and Technology of Japan and by the Tanabe Medical Frontier Conference.     

The mouse homeobox gene, S8, is expressed during embryogenesis predominantly in mesenchyme.

The murine S8 gene, originally identified by Kongsuwan et al. [EMBO J. 7(1988)2131-2138] encodes a homeodomain which resembles those of the paired family. We studied the expression pattern during mid-gestation embryogenesis of S8 by in situ hybridization. Expression was detected locally in craniofacial mesenchyme, in the limb, the heart and the somites and sclerotomes all along the axis, and was absent from the central and peripheral nervous system, splanchnopleure, and endodermal derivatives. This pattern differs considerably from that of most previously described homeobox containing genes. By genetic analysis, the gene was located on chromosome 2, about 20 cM from the HOX-4 cluster.     

Aggrecan is expressed by embryonic brain glia and regulates astrocyte development

Determination of the molecules that regulate astrocyte development has been hindered by the paucity of markers that identify astrocytic precursors in vivo. Here we report that the chondroitin sulfate proteoglycan aggrecan both regulates astrocyte development and is expressed by embryonic glial precursors. During chick brain development, the onset of aggrecan expression precedes that of the astrocytic marker GFAP and is concomitant with detection of the early glial markers GLAST and glutamine synthetase. In co-expression studies, we established that aggrecan-rich cells contain the radial glial markers nestin, BLBP and GLAST and later in embryogenesis, the astroglial marker GFAP. Parallel in vitro studies showed that ventricular zone cultures, enriched in aggrecan-expressing cells, could be directed to a GFAP-positive fate in G5-supplemented differentiation media. Analysis of the chick aggrecan mutant nanomelia revealed marked increases in the expression of the astrocyte differentiation genes GFAP, GLAST and GS in the absence of extracellular aggrecan. These increases in astrocytic marker gene expression could not be accounted for by changes in precursor proliferation or cell death, suggesting that aggrecan regulates the rate of astrocyte differentiation. Taken together, these results indicate a major role for aggrecan in the control of glial cell maturation during brain development.     

The expression of Visinin-like 1 during mouse embryonic development

Visinin like 1 (Vsnl1) encodes a calcium binding protein which is well conserved between species. It was originally found in the brain and its biological functions in central nervous system have been addressed in several studies. Low expression levels have also been found in some peripheral organs, but very little information is available regarding its physiological roles in non-neuronal tissues. Except for the kidney, the expression pattern of Vsnl1 mRNA and protein has not yet been addressed during embryogenesis. By in situ hybridization and immunolabeling we have extensively analyzed the expression pattern of Vsnl1 during murine development. Vsnl1 specifies the cardiac primordia and its expression becomes restricted to the atrial myocardium after heart looping. However, in the adult heart, Vsnl1 is expressed by all four cardiac chambers. It also serves as a specific marker for the cardiomyocyte-derived structures in the systemic and pulmonary circulation. Vsnl1 is dynamically expressed also by many other organs during development e.g. taste buds, cochlea, thyroid, tooth, salivary and adrenal gland. The stage specific expression pattern of Vsnl1 makes it a potentially useful marker particularly in studies of cardiac and vascular morphogenesis.