DNA Conformation Induces Adaptable Binding by Tandem Zinc Finger Proteins.

Tandem zinc finger (ZF) proteins are the largest and most rapidly diverging family of DNA-binding transcription regulators in mammals. ZFP568 represses a transcript of placental-specific insulin like growth factor 2 (Igf2-P0) in mice. ZFP568 binds a 24-base pair sequence-specific element upstream of Igf2-P0 via the eleven-ZF array. Both DNA and protein conformations deviate from the conventional one finger-three bases recognition, with individual ZFs contacting 2, 3, or 4 bases and recognizing thymine on the opposite strand. These interactions arise from a shortened minor groove caused by an AT-rich stretch, suggesting adaptability of ZF arrays to sequence variations. Despite conservation in mammals, mutations at Igf2 and ZFP568 reduce their binding affinity in chimpanzee and humans. Our studies provide important insights into the evolutionary and structural dynamics of ZF-DNA interactions that play a key role in mammalian development and evolution.

Double Appendix: Implications for the Emergency Department.

BACKGROUND: A double appendix, also known as vermiform appendix duplex, is a rare anomaly in humans, with a reported incidence of 1 in 25,000. The rarity of vermiform appendix duplication makes it a noteworthy medical occurrence. Approximately 100 reported cases have been documented since the first observed case in 1892. There are multiple types of appendiceal duplications, some of which include duplications of other organs. CASE REPORT: A 10-year-old boy was diagnosed with acute appendicitis by clinical examination and ultrasound. He underwent a laparoscopic appendectomy and had an unremarkable recovery. His pathology revealed acute suppurative appendicitis. Two months later, he presented to the emergency department due to bilateral lower abdominal pain with guarding and distension on examination. He underwent a computed tomography of the abdomen and pelvis secondary to concern for a postoperative abscess, which instead showed a normal-appearing retrocecal appendix containing oral contrast. The patient was diagnosed with constipation, and his symptoms resolved with an enema. Our patient had two completely separate appendices, one arising from the cecal tinea coli, and one retrocecal. Why Should an Emergency Physician Be Aware of This? Clinicians should be aware of this rare anomaly as a potential diagnosis in a patient with a history of prior appendectomy and clinical signs consistent with recurrent appendicitis. This also underscores the need for communication between doctors and patients, along with their families, to avoid delays in diagnosis in the future.

KRAB-zinc finger protein gene expansion in response to active retrotransposons in the murine lineage.

The Krüppel-associated box zinc finger protein (KRAB-ZFP) family diversified in mammals. The majority of human KRAB-ZFPs bind transposable elements (TEs), however, since most TEs are inactive in humans it is unclear whether KRAB-ZFPs emerged to suppress TEs. We demonstrate that many recently emerged murine KRAB-ZFPs also bind to TEs, including the active ETn, IAP, and L1 families. Using a CRISPR/Cas9-based engineering approach, we genetically deleted five large clusters of KRAB-ZFPs and demonstrate that target TEs are de-repressed, unleashing TE-encoded enhancers. Homozygous knockout mice lacking one of two KRAB-ZFP gene clusters on chromosome 2 and chromosome 4 were nonetheless viable. In pedigrees of chromosome 4 cluster KRAB-ZFP mutants, we identified numerous novel ETn insertions with a modest increase in mutants. Our data strongly support the current model that recent waves of retrotransposon activity drove the expansion of KRAB-ZFP genes in mice and that many KRAB-ZFPs play a redundant role restricting TE activity.

A placental growth factor is silenced in mouse embryos by the zinc finger protein ZFP568.

Insulin-like growth factor 2 (IGF2) is the major fetal growth hormone in mammals. We identify zinc finger protein 568 (ZFP568), a member of the rapidly evolving Kruppel-associated box-zinc finger protein (KRAB-ZFP) family linked primarily to silencing of endogenous retroelements, as a direct repressor of a placental-specific Igf2 transcript (designated Igf2-P0) in mice. Loss of Zfp568, which causes gastrulation failure, or mutation of the ZFP568-binding site at the Igf2-P0 promoter causes inappropriate Igf2-P0 activation. Deletion of Igf2 can completely rescue Zfp568 gastrulation phenotypes through late gestation. Our data highlight the exquisite selectivity with which members of the KRAB-ZFP family repress their targets and identify an additional layer of transcriptional control of a key growth factor regulating fetal and placental development.