Diagnosis of Seminoma With Metastasis to the Brain and Kidneys in a Moluccan Eclectus (Eclectus roratus) Using Advanced Contrast Based Imaging.

A 20-year-old male Moluccan eclectus (Eclectus roratus) was presented with a history of falling off the perch, ataxia, unilateral blindness, hyporexia, and progressive lethargy. The eclectus was found to have a leukocytosis (52 × 103 cells/µL), characterized by an absolute and relative heterophilia (42.6 × 103 cells/µL and 82%, respectively), relative lymphopenia (18%), elevated bile acids (88 µmol/L), and elevated triglycerides (236 mg/dL). Radiographic images revealed a mass effect within the caudal coelom. After 13 days of outpatient supportive care, the patient was rechecked and had normalized bile acids (<35 µmol/L), static triglycerides (232 mg/ dL), and hyperuricemia (18.6 mg/dL). Computed tomography was performed antemortem with and without iodinated contrast agent, 4 mL/kg IV over 2 minutes, and a mass was found associated with the left kidney. Due to worsening neurologic signs and involvement with surrounding structures, the owner elected euthanasia. Before the postmortem examination, a postmortem intravascular contrast agent was used to provide a more thorough visualization of internal anatomical structures, including left renal vasculature disruption, mass vasculature, caudal coelomic organ displacement, and increased irregular optic chiasm radiodensity. Postmortem, a 4 × 4.1 × 5.1-cm white to tan mass was identified. Histopathology confirmed a seminoma with metastasis to the kidneys and optic chiasm. Seminomas have been described in avian species; however, seminoma metastasis in an eclectus parrot confirmed by histopathology has not been reported, and optic chiasm metastasis of a seminoma has not been described in any avian species. This report describes postmortem computed tomographic angiography of metastatic seminoma in a Moluccan eclectus with metastasis to the optic chiasm.

Arx polyalanine expansion in mice leads to reduced pancreatic α-cell specification and increased α-cell death.

ARX/Arx is a homeodomain-containing transcription factor necessary for the specification and early maintenance of pancreatic endocrine α-cells. Many transcription factors important to pancreas development, including ARX/Arx, are also crucial for proper brain development. Although null mutations of ARX in human patients result in the severe neurologic syndrome XLAG (X-linked lissencephaly associated with abnormal genitalia), the most common mutation is the expansion of the first polyalanine tract of ARX, which results primarily in the clinical syndrome ISSX (infantile spasms). Mouse models of XLAG, ISSX and other human ARX mutations demonstrate a direct genotype-phenotype correlation in ARX-related neurologic disorders. Furthermore, mouse models utilizing a polyalanine tract expansion mutation have illustrated critical developmental differences between null mutations and expansion mutations in the brain, revealing context-specific defects. Although Arx is known to be required for the specification and early maintenance of pancreatic glucagon-producing α-cells, the consequences of the Arx polyalanine expansion on pancreas development remain unknown. Here we report that mice with an expansion mutation in the first polyalanine tract of Arx exhibit impaired α-cell specification and maintenance, with gradual α-cell loss due to apoptosis. This is in contrast to the re-specification of α-cells into ß- and δ-cells that occurs in mice null for Arx. Overall, our analysis of an Arx polyalanine expansion mutation on pancreatic development suggests that impaired α-cell function might also occur in ISSX patients.

Pancreatic α-cell specific deletion of mouse Arx leads to α-cell identity loss.

The specification and differentiation of pancreatic endocrine cell populations (α-, ß-, δ, PP- and ε-cells) is orchestrated by a combination of transcriptional regulators. In the pancreas, Aristaless-related homeobox gene (Arx) is expressed first in the endocrine progenitors and then restricted to glucagon-producing α-cells. While the functional requirement of Arx in early α-cell specification has been investigated, its role in maintaining α-cell identity has yet to be explored. To study this later role of Arx, we have generated mice in which the Arx gene has been ablated specifically in glucagon-producing α-cells. Lineage-tracing studies and immunostaining analysis for endocrine hormones demonstrate that ablation of Arx in neonatal α-cells results in an α-to-ß-like conversion through an intermediate bihormonal state. Furthermore, these Arx-deficient converted cells express ß-cell markers including Pdx1, MafA, and Glut2. Surprisingly, short-term ablation of Arx in adult mice does not result in a similar α-to-ß-like conversion. Taken together, these findings reveal a potential temporal requirement for Arx in maintaining α-cell identity.

Islet α-, ß-, and δ-cell development is controlled by the Ldb1 coregulator, acting primarily with the islet-1 transcription factor.

Ldb1 and Ldb2 are coregulators that mediate Lin11-Isl1-Mec3 (LIM)-homeodomain (HD) and LIM-only transcription factor-driven gene regulation. Although both Ldb1 and Ldb2 mRNA were produced in the developing and adult pancreas, immunohistochemical analysis illustrated a broad Ldb1 protein expression pattern during early pancreatogenesis, which subsequently became enriched in islet and ductal cells perinatally. The islet-enriched pattern of Ldb1 was similar to pan-endocrine cell-expressed Islet-1 (Isl1), which was demonstrated in this study to be the primary LIM-HD transcription factor in developing and adult islet cells. Endocrine cell-specific removal of Ldb1 during mouse development resulted in a severe reduction of hormone⁺ cell numbers (i.e., α, ß, and δ) and overt postnatal hyperglycemia, reminiscent of the phenotype described for the Isl1 conditional mutant. In contrast, neither endocrine cell development nor function was affected in the pancreas of Ldb2(-/-) mice. Gene expression and chromatin immunoprecipitation (ChIP) analyses demonstrated that many important Isl1-activated genes were coregulated by Ldb1, including MafA, Arx, insulin, and Glp1r. However, some genes (i.e., Hb9 and Glut2) only appeared to be impacted by Ldb1 during development. These findings establish Ldb1 as a critical transcriptional coregulator during islet α-, ß-, and δ-cell development through Isl1-dependent and potentially Isl1-independent control.

Nkx2.2 and Arx genetically interact to regulate pancreatic endocrine cell development and endocrine hormone expression.

Nkx2.2 and Arx are essential pancreatic transcription factors. Nkx2.2 is necessary for the appropriate specification of the islet alpha, beta, PP and epsilon cell lineages, whereas Arx is required to form the correct ratio of alpha, beta, delta and PP cells. To begin to understand the cooperative functions of Nkx2.2 and Arx in the development of endocrine cell lineages, we generated progenitor cell-specific deletions of Arx on the Nkx2.2 null background. The analysis of these mutants demonstrates that expansion of the ghrelin cell population in the Nkx2.2 null pancreas is not dependent on Arx; however, Arx is necessary for the upregulation of ghrelin mRNA levels in Nkx2.2 mutant epsilon cells. Alternatively, in the absence of Arx, delta cell numbers are increased and Nkx2.2 becomes essential for the repression of somatostatin gene expression. Interestingly, the dysregulation of ghrelin and somatostatin expression in the Nkx2.2/Arx compound mutant (Nkx2.2(null);Arx(Δpanc)) results in the appearance of ghrelin+/somatostatin+ co-expressing cells. These compound mutants also revealed a genetic interaction between Nkx2.2 and Arx in the regulation of the PP cell lineage; the PP cell population is reduced when Nkx2.2 is deleted but is restored back to wildtype numbers in the Nkx2.2(null);Arx(Δpanc) mutant. Moreover, conditional deletion of Arx in specific pancreatic cell populations established that the functions of Arx are necessary in the Neurog3+ endocrine progenitors. Together, these experiments identify novel genetic interactions between Nkx2.2 and Arx within the endocrine progenitor cells that ensure the correct specification and regulation of endocrine hormone-producing cells.