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Tuberous sclerosis complex (TSC) is a tumor suppressor gene syndrome in which hamartomas develop in multiple organ systems. Knockout and conditional alleles of Tsc1 and Tsc2 have been previously reported. Here, we describe the generation of a novel hypomorphic allele of Tsc2 (del3), in which exon 3, encoding 37 amino acids near the N terminus of tuberin, is deleted. Embryos homozygous for the del3 allele survive until E13.5, 2 days longer than Tsc2 null embryos. Embryos die from underdevelopment of the liver, deficient hematopoiesis, aberrant vascular development and hemorrhage. Mice that are heterozygous for the del3 allele have a markedly reduced kidney tumor burden in comparison with conventional Tsc2(+/-) mice. Murine embryo fibroblast (MEF) cultures that are homozygous for the del3 allele express mutant tuberin at low levels, and show enhanced activation of mTORC1, similar to Tsc2 null MEFs. Furthermore, the mutant cells show prominent reduction in the activation of AKT. Similar findings were made in the analysis of homozygous del3 embryo lysates. Tsc2-del3 demonstrates GTPase activating protein activity comparable to that of wild-type Tsc2 in a functional assay. These findings indicate that the del3 allele is a hypomorphic allele of Tsc2 with partial function due to reduced expression, and highlight the consistency of AKT downregulation when Tsc1/Tsc2 function is reduced. Tsc2-del3 mice also serve as a model for hypomorphic TSC2 missense mutations reported in TSC patients.

The tail gut is a blind extension of the hindgut into the tail fold just distal to the cloacal membrane. Remnants of this structure may form tail gut cyst. We report a 14-year-old girl with tail gut cyst that presented as acute abdomen. The patient recovered after cyst excision.

To determine the biological role of caudal-like homeobox gene CDX2, we constructed knockout mice in which its mouse homologue Cdx2 was inactivated by homologous recombination, placing a bacterial lacZ gene under the control of the Cdx2 promoter. Although the homozygous mutants died in utero around implantation, the heterozygotes were viable and fertile and expressed lacZ in the caudal region in early embryos and in the gut tissues in adults. The heterozygotes developed cecal and colonic villi by anteriorization and formed hamartomatous polyps in the proximal colon. The hamartoma started to develop at 11.5 days of gestation as an outpocket of the gut epithelium, which ceased to express the remaining Cdx2 allele. The outpocket then expanded as a partially duplicated gut but was contained as a hamartoma after birth. In adult mice, these hamartomas grew very slowly and took a benign course. None of them progressed into invasive adenocarcinomas, even at 1.5 years of age. Whereas the cecal and colonic villi expressed lacZ, the hamartoma epithelium did not, nor did it express Cdx2 mRNA from the wild-type allele. However, genomic DNA analysis of the polyp epithelium did not show a loss of heterozygosity of the Cdx2 gene, suggesting a mechanism of biallelic Cdx2 inactivation other than loss of heterozygosity. These results indicate that the Cdx2 haploin-sufficiency caused cecal and colonic villi, whereas the biallelic inactivation of Cdx2 triggered anomalous duplications of the embryonic gut epithelium, which were contained as hamartomas after birth.

An unusual case with Sturge-Weber syndrome is reported. A computed tomography study revealed the presence of gyriform calcifications in the occipital lobe, and discovered a hidden occipital subcutaneous port-wine nevus, instead of the usually expected nevus in the distribution of the first division of the trigeminal nerve. Existence of an occipital port-wine nevus, which was in the distribution of the greater occipital nerve, suggested a variation with respect to the embryogenesis of the Sturge-Weber syndrome.

Retrorectal cystic hamartomas (RCHs) are uncommon lesions of controversial pathogenesis that arise in the presacrococcygeal space. We describe the clinicopathologic features of RCHs from three adult patients. Two were asymptomatic women; the third was a man who had a pelvic abscess. All three specimens were multiloculated cysts lined by squamous, transitional, and glandular epithelium. Poorly organized collections of smooth muscle were present in the surrounding connective tissue, but no well-formed smooth-muscle coat was seen. Although RCHs possess elements of three germ-cell layers, their histologic features are similar to those of the embryonic tailgut. The male patient also had a perirenal mass that was grossly and histologically identical to the RCH. The associated kidney was malrotated. A portion of the embryonic tailgut may have been pulled cephalad by the developing kidney, inhibiting its rotation. Clinicopathologic features distinguish RCH from other retrorectal cystic lesions, including teratoma, dermoid, epidermal cyst, rectal duplication, anal duplication, and anal gland cyst.