The tyrosine kinase Syk (relative molecular mass 72,000), which is widely expressed in haematopoietic cells, becomes associated with and activated by engagement of the B-cell antigen receptor. Furthermore, it has been implicated in signalling through the receptors for interleukin-2 (IL-2), granulocyte colony-stimulating factor (G-CSF) and Fc, the T cell receptor, as well as through receptors for several platelet agonists. A homologous kinase, ZAP-70, is crucial in signalling through the T-cell receptor and in T-cell development. Using homologous recombination in embryonic stem cells, we created mice null for the syk gene which showed petechiae in utero and died shortly after birth. Irradiated mice reconstituted with Syk-deficient fetal liver showed a block in B-cell development at the pro-B to pre-B cell transition, consistent with a key role for Syk in pre-B-cell receptor signalling. Despite the production of small numbers of immature B cells, Syk-deficient radiation chimaeras failed to accumulate mature B cells, indicating a possible role for this protein in the production or maintenance of mature B cells. In addition, whereas the development of alpha beta T cells proceeded normally, Syk-deficient mice showed impaired development of thymocytes using the V gamma 3 variable region gene (V gamma 3+ thymocytes). Finally, we show that Syk is not required for signalling through the IL-2 and G-CSF receptors.
Background
Sensory features are highly prevalent and heterogeneous among children with ASD. There is a need to identify homogenous groups of children with ASD based on sensory features (i.e., sensory subtypes) to inform research and treatment.
Methods
Sensory subtypes and their stability over one year were identified through latent profile transition analysis (LPTA) among a national sample of children with ASD. Data were collected from caregivers of children with ASD ages 2-12 years at two time points (Time 1 N=1294; Time 2 N=884).
Results
Four sensory subtypes (Mild; Sensitive-Distressed; Attenuated-Preoccupied; Extreme-Mixed) were identified, which were supported by fit indices from the LPTA as well as current theoretical models that inform clinical practice. The Mild and Extreme-Mixed subtypes reflected quantitatively different sensory profiles, while the Sensitive-Distressed and Attenuated-Preoccupied subtypes reflected qualitatively different profiles. Further, subtypes reflected differential child (i.e., gender, developmental age, chronological age, autism severity) and family (i.e., income, mother's education) characteristics. Ninety-one percent of participants remained stable in their subtypes over one year.
Conclusions
Characterizing the nature of homogenous sensory subtypes may facilitate assessment and intervention, as well as potentially inform biological mechanisms.
The protein tyrosine kinase p72syk (Syk) is expressed in a variety of hematopoietic cell types, including B cells, thymocytes, mast cells and others. Both the activity and phosphotyrosine content of this enzyme increase in these cells in response to engagement of the appropriate cell surface receptors. Herein, we describe the cloning of murine Syk and its expression in Sf9 cells as a catalytically active protein. Full-length Syk and a catalytically active 42.5 kDa carboxyl terminal fragment were also expressed as glutathione S-transferase fusion proteins. Comparative reverse phase HPLC and 40% alkaline gel analysis of tryptic digests of phosphorylated Syk demonstrated that all of the major sites of autophosphorylation were also present in GST-Syk and all but one were contained in the 42.5 kDa fragment. The sites of autophosphorylation were identified using a combination of Edman sequencing and mass spectrometric analysis. Ten sites were identified. One site is located in the amino terminal half of the molecule between the two tandem Src homology 2 (SH2) domains. Five sites are located in the hinge region located between the carboxyl terminal SH2 domain and the kinase domain. Two sites lie in the kinase domain within the catalytic loop and two near the extreme carboxyl terminus. Sequences of phosphorylation sites located within the hinge region predict that Syk serves as a docking site for other SH2 domain-containing proteins. Consistent with this prediction, autophosphorylated Syk efficiently binds the carboxyl terminal SH2 domain of phospholipase C-gamma 1.
Prenatal exposure to organophosphate pesticides (OPs) has been associated with adverse neurodevelopmental outcomes in childhood, including low IQ, Pervasive Developmental Disorder (PDD), attention problems and ADHD. Many of these disorders involve impairments in social functioning. Thus, we investigated the relationship between biomarkers of prenatal OP exposure and impaired reciprocal social behavior in childhood, as measured by the Social Responsiveness Scale (SRS). Using a multi-ethnic urban prospective cohort of mother-infant pairs in New York City recruited between 1998 and 2002 (n=404) we examined the relation between third trimester maternal urinary levels of dialkylphosphate (ΣDAP) OP metabolites and SRS scores among 136 children who returned for the 7–9 year visit. Overall, there was no association between OPs and SRS scores, although in multivariate adjusted models, associations were heterogeneous by race and by sex. Among blacks, each 10-fold increase in total diethylphosphates (ΣDEP) was associated with poorer social responsiveness (β = 5.1 points, 95% confidence interval (CI) 0.8, 9.4). There was no association amongst whites or Hispanics, or for total ΣDAP or total dimethylphosphate (ΣDMP) biomarker levels. Additionally, stratum-specific models supported a stronger negative association among boys for ΣDEPs (β = 3.5 points, 95% CI 0.2, 6.8), with no notable association among girls. Our results support an association of prenatal OP exposure with deficits in social functioning among blacks and among boys, although this may be in part reflective of differences in exposure patterns.
This simple sample preparation approach will be beneficial to bioanalytical laboratories engaged in the LC-MS/MS quantification of large therapeutic proteins in biological matrices.
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