” This motif is mostly composed of glutamic and aspartic acids 5 and increases the retention of proteins at the plasma membrane 6. Besides HS1, many other binding partners of HAX1 were identified by yeast two-hybrid screens, involving several virus-associated

proteins 7–9, Omi/HtrA2 10, PKD2 3, cortactin/EMS1 3, the α subunit of G13 heterotrimeric G protein 11, the cytoplasmic tail of αvβ6 integrin 12 and ILK 13, strongly emphasizing a role of HAX1 in both apoptotic and cell motility/actin dynamics processes. However, these processes are not mutually exclusive, as actin dynamics in eukaryotic Torin 1 manufacturer cells also controls cellular viability through a mitochondrial dependent pathway, as demonstrated in yeast 14. Recently, it was shown that homozygous mutations in the human HAX1 gene cause autosomal recessive severe congenital neutropaenia or Kostmann disease. The primary immunodeficiency syndrome is characterized by the increased susceptibility of HAX1-deficient neutrophils and myeloid progenitors to

undergo apoptosis due to poor regulation of the mitochondrial membrane potential 15. Furthermore, HAX1 was found to be highly expressed in psoriasis, a chronic inflammatory GPCR Compound Library purchase disease characterized by epidermal hyperplasia and disturbed apoptosis of keratinocytes 16 and in various types of human malignancies 12, 16. Recent findings 5, 17 showed that human HAX1 constitute a “family” of protein isoforms produced by alternative splicing. By means of a targeted disruption of the Hax1 gene in mice, we demonstrate that HAX1 is crucial for early and late stages of B-cell development and HSC homeostasis but dispensable for splenic B- and T-cell proliferation in vitro. Furthermore, Hax1−/− splenic B cells show reduced levels of CXCR4, which is known

to be necessary for germinal centre organization 18. CXCL12, the ligand for CXCR4, is expressed by osteoblasts and reticular cells, serving as niches for early B-cell development 19. The decreased expression of CXCR4 might explain the observed defects in B-cell development as result of impaired migration behaviour of B-cell precursors. However, adoptive transfer experiments demonstrated that the defects are not exclusively Fossariinae B-cell intrinsic because transfer of Hax1−/− lineage-negative (Lin−) bone marrow cells led to the reconstitution of the respective cell populations. Thus, a HAX1-deficient bone marrow environment probably cannot sufficiently provide the essential factors for proper lymphocyte development. Targeted ES cells (ESC) were generated according to the standard Cre/loxP-mediated gene targeting technique 20. BALB/c ESC genomic DNA was used as a template for PCR amplification of the Hax1 genomic locus. For the construction of the target vector, a loxP-flanked Neor/TK cassette was inserted between exons 1 and 2, followed by a third singular loxP site 3-prime of exon 3 (Fig. 1A).