Indiana University-Purdue University Indianapolis (IUPUI) / The basic Helix-Loop-Helix (bHLH) transcription factors Hand1 and Hand2 play critical roles in the development of multiple organ systems during embryogenesis. The dynamic expression patterns of these two factors within developing tissues obfuscates their respective unique and redundant organogenic functions. To define cell lineages potentially dependent upon Hand gene expression, we generated a mutant allele in which the coding region of Hand1 is replaced by Cre recombinase. Subsequent Cre-mediated activation of β-galactosidase or eYFP reporter alleles enabled lineage trace analyses that clearly define the fate of Hand1-expressing cells. Comparisons between Hand1 expression and Hand1-lineage greatly refine our understanding of its dynamic spatio-temporal expression domains and raise the possibility of novel Hand1 functions in structures not thought to be Hand1-dependent. To genetically examine functional overlap between Hand1 and Hand2, we conditionally deleted Hand2 from Hand1-expressing cells. Hand2 conditional knockout mice die midgestation and exhibit cardiovascular and limb defects. Moreover, Hand2 lineage-restricted deletion from the proepicardial organ results in defective epicardialization and failure to form coronary arteries. Together, these novel data demonstrate a hierarchal relationship whereby transient Hand1 expression within the septum transversum defines epicardial precursors that depend upon subsequent Hand2 function.

Une craniosynostose est une pathologie caractérisée par la fusion prématurée d'une ou plusieurs sutures crâniennes. C'est un défaut de naissance assez fréquent (1/2500 naissances) qui résulte en une forme anormale du crâne et qui peut être accompagné d'une déficience mentale dans certains cas. Des mutations du gène TWIST1, qui encode un facteur de transcription basique Helix-Loop-Helix (bHLH) de classe II, causent le syndrome de Saethre-Chotzen qui est associé à une synostose de la suture coronale (El Ghouzzi et al. 1997; Howard et al. 1997). Un nouveau gène a récemment été découvert comme étant une nouvelle cause du syndrome Saethre-Chotzen ainsi que de synostose coronale asyndromique (Sharma, Fenwick, Brockop, et al., 2013): il s'agit du gène TCF12, qui encode un facteur de transcription bHLH de classe I.Nous démontrons qu'une reduction de l'expression génique de Twist1 et Tcf12 chez la souris cause une synostose coronale, et nous suggérons que les protéines bHLH Twist1 et Tcf12 forment des hétérodimères dont le dosage est critique pour le développement de la suture coronale.Nous nous concentrons aussi sur Twist1 et prouvons que son expression est requise dans les tissus dérivant du mésoderme ainsi que ceux dérivant des crêtes neurales pour le développement normal de la suture coronale.De plus, nous notons que dans la suture coronale, Twist1 exclut Notch2 afin de garder la suture ouverte, et beta-catenin joue un rôle dans la maintenance de l'ouverture de la suture en ciblant Jagged1 lors du développement de la suture coronale chez la souris.Enfin, nous mentionnons de nouveaux gènes qui pourraient avoir un impact sur le développement normal de la suture coronale: Aggrecan, Goosecoid, Gucy1a3 et Gucy1b3. / Craniosynostosis, the premature fusion of one or more cranial sutures, is a common birth defect (1/2500 live births) that results in abnormalities in skull shape and sometimes in neurological deficiencies (Wilkie, 1997; Wilkie and Morriss-Kay, 2001). Mutations in TWIST1, which encodes a class II basic helix-loop-helix (bHLH) transcription factor, cause Saethre-Chotzen syndrome, associated with coronal synostosis (El Ghouzzi et al. 1997; Howard et al. 1997). We recently discovered a new craniosynostosis gene, TCF12, which encodes a class I bHLH transcription factor. Tcf12 causes.Saethre-Chotzen syndrome and asyndromic coronal synostosis. (Sharma, Fenwick, Brockop, et al., 2013). We show that a reduction in the dosage of Twist1 and Tcf12 in mouse causes coronal synostosis, and we suggest that the Twist1 and Tcf12 form heterodimers whose dosage is critical for coronal suture development. We also demonstrate that Twist1 is required in both neural-crest and mesoderm-derived tissues for the normal coronal suture development. Moreover, we show that in the coronal suture, Twist1 excludes Notch2 thus maintaining suture patency. and we show that beta-catenin also plays a role in the maintenance of suture patency by regulating Jagged1. Finally, we identified Aggrecan, Goosecoid, Gucy1a3 and Gucy1b3 as Twist1-regulated genes that could have an impact on the normal development of the coronal suture.

published_or_final_version / abstract / Anatomy / Doctoral / Doctor of Philosophy

In mammals, circadian rhythms are generated by transcriptional-translational feedback loops consisting of a set of clock genes and their protein products. Among them, Bmal1 is a critical clock gene in generating and maintaining circadian rhythms. Moreover, orphan nuclear receptors REV-ERBs and RORs were known to respectively repress and activate Bmal1 transcription. In our study, we further demonstrated that: (1) REV-ERBalpha might be the main regulator in maintaining Bmal1 oscillation in thymus. (2) Rorgamma mRNA is constant in muscle and testis, and rhythmic in liver, while Rorgammat mRNA is only expressed in thymus, at constant levels. Moreover, the expressions of these two Rorgamma isoforms are affected in Clock mutant mice in a distinct way. (3) RORgamma and RORgammat can activate Bmal1 transcription at a similar level. (4) Rorgamma is a clock-controlled gene. Altogether, our results suggest that the crucial role of REV-ERBs and RORs in peripheral clocks. Furthermore, our work highlights functional differences among mammalian peripheral clocks, which provides important insights into the complexity of the circadian system.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 61-63).

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Vita. Bibliography: 123-135.

Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2001. / Vita. Bibliography: 108-125.

Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2003. / Vita. Bibliography: References located at the end of each chapter.

Thesis (M.S.) -- University of Texas Southwestern Medical Center at Dallas, 2003. / Vita. Bibliography: 45-48.