Megaesophagus in a Line of Transgenic Rats: A Model of Achalasia

Megaesophagus is defined as the abnormal enlargement or dilatation of the esophagus, characterized by a lack of normal contraction of the esophageal walls. This is called achalasia when associated with reduced or no relaxation of the lower esophageal sphincter (LES). To date, there are few naturally occurring models for this disease. A colony of transgenic (Pvrl3-Cre) rats presented with megaesophagus at 3 to 4 months of age; further breeding studies revealed a prevalence of 90% of transgene-positive animals having megaesophagus. Affected rats could be maintained on a total liquid diet long term and were shown to display the classic features of dilated esophagus, closed lower esophageal sphincter, and abnormal contractions on contrast radiography and fluoroscopy. Histologically, the findings of muscle degeneration, inflammation, and a reduced number of myenteric ganglia in the esophagus combined with ultrastructural lesions of muscle fiber disarray and mitochondrial changes in the striated muscle of these animals closely mimic that seen in the human condition. Muscle contractile studies looking at the response of the lower esophageal sphincter and fundus to electrical field stimulation, sodium nitroprusside, and L-nitro-L-arginine methyl ester also demonstrate the similarity between megaesophagus in the transgenic rats and patients with achalasia. No primary cause for megaesophagus was found, but the close parallel to the human form of the disease, as well as ease of care and manipulation of these rats, makes this a suitable model to better understand the etiology of achalasia as well as study new management and treatment options for this incurable condition.National Institutes of Health (U.S.) (Grant T32OD011141)National Institutes of Health (U.S.) (Grant P30ES002109

Restriction of endogenous T cell antigen receptor β rearrangements to Vβ14 through selective recombination signal sequence modifications

T cell antigen receptor (TCR)β V(D)J variable region exon assembly is ordered, with Dβ to Jβ rearrangements occurring before joining of Vβs to a DJβ complex. Germ-line V(D)J segments are flanked by recombination signal (RS) sequences, which consist of heptamers and nonamers separated by a spacer of 12 (12-RS) or 23 (23-RS) bp. V(D)J recombination is restricted by the 12/23 rule; joining occurs only between gene segments flanked by 12-RSs and 23-RSs. Vβ segments have 23-RSs and Jβ segments 12-RSs, which based on the 12/23 rule should allow direct joining. However, Vβ segments rearrange only to DJβ complexes and not Jβ segments, because of restrictions beyond 12/23 (B12/23) that make the Vβ23-RS incompatible with the Jβ12-RS. To determine whether direct Vβ to Jβ joining occurs if flanking RSs are B12/23 compatible, we generated mice whose lymphocytes contained replacement of the Vβ1412-RS with the 3′Dβ112-RS on a TCRβ allele lacking Dβ segments (the Jβ1(M6) allele). Mice heterozygous for the Jβ1(M6) allele had dramatically increased Vβ14(+) thymocyte and T cell numbers and decreased numbers of cells expressing other Vβs. This altered Vβ repertoire resulted from direct Vβ14 to Jβ1 rearrangements on the Jβ1(M6) allele. Mice harboring lymphocytes homozygous for Jβ1(M6) allele developed normal thymocyte and T cell numbers with all expressing Vβ14. Our findings show that selective RS modifications enforce rearrangement of a specific Vβ gene segment and demonstrate the importance of B12/23 mechanisms for ensuring generation of diverse TCRβ repertoires