Actin and CDC-42 contribute to nuclear migration through constricted spaces in C. elegans

Successful nuclear migration through constricted spaces between cells or in the extracellular matrix relies on the ability of the nucleus to deform. Little is known about how this takes place in vivo. We have studied confined nuclear migration in Caenorhabditis elegans larval P cells, which is mediated by the LINC complex to pull nuclei towards the minus ends of microtubules. Null mutations of the LINC component unc-84 lead to a temperature-dependent phenotype, suggesting a parallel pathway for P-cell nuclear migration. A forward genetic screen for enhancers of unc-84 identified cgef-1 (CDC-42 guanine nucleotide exchange factor). Knockdown of CDC-42 in the absence of the LINC complex led to a P-cell nuclear migration defect. Expression of constitutively active CDC-42 partially rescued nuclear migration in cgef-1; unc-84 double mutants, suggesting that CDC-42 functions downstream of CGEF-1. The Arp2/3 complex and non-muscle myosin II (NMY-2) were also found to function parallel to the LINC pathway. In our model, CGEF-1 activates CDC-42, which induces actin polymerization through the Arp2/3 complex to deform the nucleus during nuclear migration, and NMY-2 helps to push the nucleus through confined spaces.

The Nesprin-1/-2 ortholog ANC-1 regulates organelle positioning in C. elegans independently from its KASH or actin-binding domains

KASH proteins in the outer nuclear membrane comprise the cytoplasmic half of linker of nucleoskeleton and cytoskeleton (LINC) complexes that connect nuclei to the cytoskeleton. Caenorhabditis elegans ANC-1, an ortholog of Nesprin-1/2, contains actin-binding and KASH domains at opposite ends of a long spectrin-like region. Deletion of either the KASH or calponin homology (CH) domains does not completely disrupt nuclear positioning, suggesting neither KASH nor CH domains are essential. Deletions in the spectrin-like region of ANC-1 led to significant defects, but only recapitulated the null phenotype in combination with mutations in the transmembrane (TM) span. In anc-1 mutants, the endoplasmic reticulum ER, mitochondria, and lipid droplets were unanchored, moving throughout the cytoplasm. The data presented here support a cytoplasmic integrity model where ANC-1 localizes to the ER membrane and extends into the cytoplasm to position nuclei, ER, mitochondria, and other organelles in place.

Diagnostic and therapeutic approach to incidental adrenal mass

Finding an adrenal mass incidentally during a routine CT scan of the abdomen has occurred with increasing frequency since the introduction of the CT scan. Most of the reported tumors have been nonfunctional and benign adrenal adenomas. Other benign adrenal tumors also have been reported. The functional capacity and size of the tumor, the age of the patient, and the radiologic features of the mass are important factors in differentiating malignant from benign adrenal tumors. A diagnostic and therapeutic approach is recommended to avoid unnecessary surgery for benign disease.

Benign nonfunctional tumors of adrenal gland

Seven cases of benign nonfunctional adrenal tumors are presented. All except one were found accidentally by computerized tomography (CT) scan during a workup of an abdominal condition. In 1 patient the CT scan was ordered to evaluate hirsutism, but subsequent endocrine studies were found to be normal. Asymptomatic adrenal tumors found by abdominal CT scans are usually benign. Careful selection of individual patients and a possible nonsurgical follow-up are suggested.

Regression of pituitary tumor after thyroid replacement in primary hypothyroidism

We report the case of a young woman with primary hypothyroidism in whom a large pituitary tumor with suprasellar extension and the amenorrhea-galactorrhea syndrome developed. After nine months of thyroid replacement there was clinical and radiologic evidence of tumor regression.