CLEC-2 and Syk in the megakaryocytic/platelet lineage are essential for development

The C-type lectin receptor CLEC-2 signals through a pathway that is critically dependent on the tyrosine kinase Syk. We show that homozygous loss of either protein results in defects in brain vascular and lymphatic development, lung inflation, and perinatal lethality. Furthermore, we find that conditional deletion of Syk in the hematopoietic lineage, or conditional deletion of CLEC-2 or Syk in the megakaryocyte/platelet lineage, also causes defects in brain vascular and lymphatic development, although the mice are viable. In contrast, conditional deletion of Syk in other hematopoietic lineages had no effect on viability or brain vasculature and lymphatic development. We show that platelets, but not platelet releasate, modulate the migration and intercellular adhesion of lymphatic endothelial cells through a pathway that depends on CLEC-2 and Syk. These studies found that megakaryocyte/platelet expression of CLEC-2 and Syk is required for normal brain vasculature and lymphatic development and that platelet CLEC-2 and Syk directly modulate lymphatic endothelial cell behavior in vitro.     

The folliculin-FNIP1 pathway deleted in human Birt-Hogg-Dube syndrome is required for murine B-cell development

Birt-Hogg-Dubé (BHD) syndrome is an autosomal dominant disorder characterized by cutaneous fibrofolliculomas, pulmonary cysts, and kidney malignancies. Affected individuals carry germ line mutations in folliculin (FLCN), a tumor suppressor gene that becomes biallelically inactivated in kidney tumors by second-hit mutations. Similar to other factors implicated in kidney cancer, FLCN has been shown to modulate activation of mammalian target of rapamycin (mTOR). However, its precise in vivo function is largely unknown because germ line deletion of Flcn results in early embryonic lethality in animal models. Here, we describe mice deficient in the newly characterized folliculin-interacting protein 1 (Fnip1). In contrast to Flcn, Fnip1(-/-) mice develop normally, are not susceptible to kidney neoplasia, but display a striking pro-B cell block that is entirely independent of mTOR activity. We show that this developmental arrest results from rapid caspase-induced pre-B cell death, and that a Bcl2 transgene reconstitutes mature B-cell populations, respectively. We also demonstrate that conditional deletion of Flcn recapitulates the pro-B cell arrest of Fnip1(-/-) mice. Our studies thus demonstrate that the FLCN-FNIP complex deregulated in BHD syndrome is absolutely required for B-cell differentiation, and that it functions through both mTOR-dependent and independent pathways.     

Growth hormone regimens in Australia: analysis of the first 3 years of treatment for idiopathic growth hormone deficiency and idiopathic short stature

Objective To investigate response to growth hormone (GH) in the first, second and third years of treatment for all idiopathic GH‐deficient (GHD) and idiopathic short stature (ISS) patients in Australia. Context Eligibility for subsidized GH treatment in Australia is determined on auxological criteria for the indication of Short Stature and Slow Growth (SSSG), which includes ISS (SSSG‐ISS). The biochemical GHD (BGHD, peak GH < 10 mU/l) and SSSG indications are treated similarly: starting dose of 4·5 mg/m²/week with provision for incremental dosing. Some ISS patients were specifically diagnosed with familial short stature (SSSG‐FSS). Design Responses for each year of treatment for BGHD, SSSG‐ISS and SSSG‐FSS cohorts were compared in relation to influencing variables and with international benchmarks. The effect of incremental dosing was assessed. Patients Australian BGHD, SSSG‐ISS and SSSG‐FSS patients who had completed 1, 2, or 3 years of treatment and were currently receiving GH. Measurements Growth hormone dose, change in height‐standard deviation score (ΔSDS) and growth velocity (GV). Results First‐year response was 2–3 times greater than that in subsequent years: ΔSDS_{1st year} = 0·92, 0·50 and 0·46 for BGHD, SSSG‐ISS and SSSG‐FSS, respectively. Responses were similar to international reports and inversely related to age at commencement of GH. First‐year GV‐for‐age for BGHD patients was similar to international standards for idiopathic GHD. However, girls had an inferior response to boys when treatment commenced at <6 years of age. First‐year GV‐for‐age for SSSG‐ISS/FSS patients was less than ISS standards. Dose increments attenuated the first‐ to second‐year decline in response to BGHD but marginally improved the responses for SSSG‐ISS/FSS. Conclusions The Australian auxology‐based GH programme produces comparable responses to international programmes. A lower starting dose is offset by the initiation of treatment at younger ages. Incremental dosing does not appear optimal. A first‐year dose of 6·4–6·9 mg/m²/week for GHD and 8·9 mg/m²/week for ISS with early commencement of GH treatment may be most efficacious.