These transgenic animals also exhibited conotruncal heart malformations and outflow tract obstructions ( Ewart et al., 1997 Huang et al., 1998). Some insights into this question have since come from the analysis of transgenic mice (referred to as CMV43) in which О± 1 connexin is overexpressed in subpopulations of neural crest cells and their progenitors in the dorsal neural tube. However, since very little О± 1 connexin is normally found in this region of the developing heart ( Gourdie et al., 1992), the phenotype of the KO mice has not been very informative as to the role of О± 1 connexin gap junctions in heart morphogenesis. Studies of the О± 1 connexin knockout (KO) 1 mice have shown a role for this connexin protein in heart morphogenesis, since mice deficient in О± 1 connexin gap junctions die soon after birth because of conotruncal heart malformations and pulmonary outflow obstruction ( Reaume et al., 1995). The О± 1 connexin gap junction gene (also referred to as Cx43) is expressed in a developmentally regulated manner in many different regions of the mouse embryo (Ruangvoravat and Lo, 1992 Yancey et al., 1992). Because gap junctions are found from very early stages of embryogenesis, it has been suggested that they mediate cellвЂ“cell signaling events involved in patterning, differentiation, and development ( Guthrie and Gilula, 1989 Warner, 1992 Lo, 1996). Given the prevalence of gap junctions, it is likely that cellвЂ“cell communication via gap junctions mediates cell signaling involved in the maintenance of tissue homeostasis and in regulating growth and proliferation ( Loewenstein, 1979). Most cells or tissues express multiple connexin genes and show functional coupling via gap junctions ( Bennett et al., 1991 Bruzzone et al., 1996). These channels are made up of a hexameric array of proteins encoded by a multigene family known as the connexins ( Willecke et al., 1991 Kumar and Gilula, 1992). G ap junctions provide membrane channels, which allow the passage of ions and small molecules between cells. Furthermore, they indicate that cardiac neural crest perturbation is the likely underlying cause for heart defects in mice with the gain or loss of О± 1 connexin function. Overall, these findings suggest that gap junction communication mediated by О± 1 connexins plays an important role in cardiac neural crest migration. The latter observation suggests that cardiac neural crest cells may have a role in modulating growth and development of nonвЂ“neural crestвЂ“ derived tissues. Surprisingly, this was accompanied by cell proliferation changes, not in the cardiac neural crest cells, but in the myocardium- an elevation in the CMV43 mice vs. These studies showed more lacZ-positive cells in the outflow septum in the CMV43 transgenic mice, while a reduction was observed in the О± 1 connexin KO mice.

To determine the possible relevance of these findings to neural crest migration in vivo, a lacZ transgene was used to visualize the distribution of cardiac neural crest cells in the outflow tract. Further analysis using oleamide to downregulate gap junction communication in nontransgenic outgrowth cultures showed that this independent method of reducing gap junction communication in cardiac crest cells also resulted in a reduction in the rate of crest migration. Dye coupling analysis in neural crest cells in the outgrowth cultures and also in the living embryos showed an elevation of gap junction communication in the CMV43 transgenic mice, while a reduction was observed in the FC transgenic and О± 1 connexin KO mice. hemizygous О± 1 connexin KO and CMV43 embryos, respectively. Migration changes occurred in step with connexin gene or transgene dosage in the homozygous vs. These studies showed that the migration rate of cardiac neural crest was increased in the CMV43 embryos, but decreased in the FC transgenic and О± 1 connexin KO embryos. To elucidate the possible basis for the quantitative requirement for О± 1 connexin gap junctions in cardiac development, a neural crest outgrowth culture system was used to examine migration of neural crest cells derived from CMV43 transgenic embryos overexpressing О± 1 connexins, and from О± 1 connexin knockout (KO) mice and FC transgenic mice expressing a dominant-negative О± 1 connexin fusion protein. Previous studies showed that conotruncal heart malformations can arise with the increase or decrease in О± 1 connexin function in neural crest cells.

7 days to die alpha 10.4 mouse