Murine Surf4 is essential for early embryonic development

Newly synthesized proteins co-translationally inserted into the endoplasmic reticulum (ER) lumen may be recruited into anterograde transport vesicles by their association with specific cargo receptors. We recently identified a role for the cargo receptor SURF4 in facilitating the secretion of PCSK9 in cultured cells. To examine the function of SURF4 in vivo, we used CRISPR/Cas9-mediated gene editing to generate mice with germline loss-of-function mutations in Surf4. Heterozygous Surf4+/- mice exhibit grossly normal appearance, behavior, body weight, fecundity, and organ development, with no significant alterations in circulating plasma levels of PCSK9, apolipoprotein B, or total cholesterol, and a detectable accumulation of intrahepatic apoliprotein B. Homozygous Surf4-/- mice exhibit embryonic lethality, with complete loss of all Surf4-/- offspring between embryonic days 3.5 and 9.5. In contrast to the milder murine phenotypes associated with deficiency of known SURF4 cargoes, the embryonic lethality of Surf4-/- mice implies the existence of additional SURF4 cargoes or functions that are essential for murine early embryonic development

Genome‐wide linkage analysis and whole‐exome sequencing identifies an ITGA2B mutation in a family with thrombocytopenia

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150531/1/bjh15961_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150531/2/bjh15961.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150531/3/bjh15961-sup-0001-DataS1.pd

Spontaneous 8bp Deletion in Nbeal2 Recapitulates the Gray Platelet Syndrome in Mice.

During the analysis of a whole genome ENU mutagenesis screen for thrombosis modifiers, a spontaneous 8 base pair (bp) deletion causing a frameshift in exon 27 of the Nbeal2 gene was identified. Though initially considered as a plausible thrombosis modifier, this Nbeal2 mutation failed to suppress the synthetic lethal thrombosis on which the original ENU screen was based. Mutations in NBEAL2 cause Gray Platelet Syndrome (GPS), an autosomal recessive bleeding disorder characterized by macrothrombocytopenia and gray-appearing platelets due to lack of platelet alpha granules. Mice homozygous for the Nbeal2 8 bp deletion (Nbeal2gps/gps) exhibit a phenotype similar to human GPS, with significantly reduced platelet counts compared to littermate controls (p = 1.63 x 10-7). Nbeal2gps/gps mice also have markedly reduced numbers of platelet alpha granules and an increased level of emperipolesis, consistent with previously characterized mice carrying targeted Nbeal2 null alleles. These findings confirm previous reports, provide an additional mouse model for GPS, and highlight the potentially confounding effect of background spontaneous mutation events in well-characterized mouse strains. PLos One 2016 Mar 7; 11(3):e0150852

TPP1 mutagenesis screens unravel shelterin interfaces and functions in hematopoiesis

Telomerase catalyzes chromosome end replication in stem cells and other long-lived cells. Mutations in telomerase or telomere-related genes result in diseases known as telomeropathies. Telomerase is recruited to chromosome ends by the ACD/TPP1 protein (TPP1 hereafter), a component of the shelterin complex that protects chromosome ends from unwanted end joining. TPP1 facilitates end protection by binding shelterin proteins POT1 and TIN2. TPP1 variants have been associated with telomeropathies but remain poorly characterized in vivo. Disease variants and mutagenesis scans provide efficient avenues to interrogate the distinct physiological roles of TPP1. Here, we conduct mutagenesis in the TIN2- and POT1-binding domains of TPP1 to discover mutations that dissect TPP1’s functions. Our results extend current structural data to reveal that the TPP1-TIN2 interface is more extensive than previously thought and highlight the robustness of the POT1-TPP1 interface. Introduction of separation-of-function mutants alongside known TPP1 telomeropathy mutations in mouse hematopoietic stem cells (mHSCs) lacking endogenous TPP1 demonstrated a clear phenotypic demarcation. TIN2- and POT1-binding mutants were unable to rescue mHSC failure resulting from end deprotection. In contrast, TPP1 telomeropathy mutations sustained mHSC viability, consistent with their selectively impacting end replication. These results highlight the power of scanning mutagenesis in revealing structural interfaces and dissecting multifunctional genes

Functions of the COPII gene paralogs SEC23A and SEC23B are interchangeable in vivo

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Comparison of CBCs.

<p>Platelet counts are lower in <i>Nbeal2</i>^{<i>gps/gps</i>} mice compared to control mice in both set 1 (A) and set 2 (B) mice while hemoglobin levels are similar between the two groups (C). <i>Nbeal2</i>^{<i>gps/gps</i>} mice from set 1 exhibit significant neutropenia (D), which is not observed in set 2 by CBC (E) or flow cytometry (F). Mean platelet volume (G) and area (H) do not differ in set 1 mice, but show an increase in size for <i>Nbeal2</i>^{<i>gps/gps</i>} mice in set 2 (I).</p

Deficiency in platelet alpha granules.

<p><i>Nbeal2</i>^{<i>gps/gps</i>} platelets appear pale compared to wildtype (black arrows, A). Transmission electron microscopy (TEM) images show dark alpha granules in wildtype platelets (black arrows), which are missing in <i>Nbeal2</i>^{<i>gps/gps</i>} platelets. Red arrows indicate mitochondria (B).</p