Extracellular matrices (ECM) are secreted molecules that constitute the cell microenvironment, composed of a dynamic and complex array of glycoproteins, collagens, glycosaminoglycans and proteoglycans. ECM provides the bulk, shape and strength of many tissues in vivo, such as basement membrane, bone and cartilage. In vitro, most animal cells can only grow when they are attached to surfaces through ECM. ECM is also the substrate for cell migration. However, ECM provides much more than just mechanical and structural support, with implications in developmental patterning, stem cell niches and cancer. ECM imparts spatial context for signalling events by various cell surface growth factor receptors and adhesion molecules such as integrins. The external physical properties of ECM may also have a role in the signalling process. ECM molecules can be flexible and extendable, and mechanical tension can expose cryptic sites, which could further interact with growth factors or their receptors. ECM proteins and structures can determine the cell behaviour, polarity, migration, differentiation, proliferation and survival by communicating with the intracellular cytoskeleton and transmission of growth factor signals. Integrins and proteoglycans are the major ECM adhesion receptors which cooperate in signalling events, determining the signalling outcomes, and thus the cell fate. This review focuses on the emerging concept of spatial cell biology of ECM, especially the current understanding of integrins and heparan sulphate proteoglycans as the essential cellular machineries that sense, integrate and respond to the physical and chemical environmental information either by directly connecting with the local adhesion sites or by regulating global cellular processes through growth factor receptor signalling pathways, leading to the integration of both external and internal signals in space and time.

Cyclin E–Cdk2 kinase activation is an essential step in Myc‐induced proliferation. It is presumed that this requires sequestration of G1 cell cycle inhibitors p27 Kip1 and p21 Cip1 (Ckis) via a Myc‐induced protein. We provide biochemical and genetic evidence to show that this sequestration is mediated via induction of cyclin D1 and/or cyclin D2 protein synthesis rates. Consistent with this conclusion, primary cells from cyclin D1−/− and cyclin D2−/− mouse embryos, unlike wild‐type controls, do not respond to Myc with increased proliferation, although they undergo accelerated cell death in the absence of serum. Myc sensitivity of cyclin D1−/− cells can be restored by retroviruses expressing either cyclins D1, D2 or a cyclin D1 mutant forming kinase‐defective, Cki‐binding cyclin–cdk complexes. The sequestration function of D cyclins thus appears essential for Myc‐induced cell cycle progression but dispensable for apoptosis.

Defects of either anosmin-1 or fibroblast growth factor receptor 1 (FGFR1) are known to underlie hereditary Kallmann's syndrome (KS), a human disorder of olfactory and gonadotropin-releasing hormone (GnRH) neuronal ontogeny. Here, we report a functional interaction between anosmin-1 and the FGFR1-FGF2-heparan sulfate complex, leading to amplified responses in the FGFR1 signaling pathway. In human embryonic GnRH olfactory neuroblasts, wild-type anosmin-1, but not proteins with loss-of-function KS mutations, induces neurite outgrowth and cytoskeletal rearrangements through FGFR1-dependent mechanisms involving p42/44 and p38 mitogen-activated protein kinases and Cdc42/Rac1 activation. Furthermore, anosmin-1 enhances FGF2 signaling specifically through FGFR1 IIIc in heterologous BaF3 lymphoid cells in a heparan sulfate-dependent manner. Our study provides compelling evidence for anosmin-1 as an isoform-specific co-ligand modulator of FGFR signaling that amplifies and specifies FGFR1 signaling responses during human nervous system development and defines a mechanism underlying the link between autosomal and X-linked KS.

The proper development and coordination of the hypothalamic-pituitary-gonadal (HPG) axis are essential for normal reproductive competence. The key factor that regulates the function of the HPG axis is gonadotrophin-releasing hormone (GnRH). Timely release of GnRH is critical for the onset of puberty and subsequent sexual maturation. Misregulation in this system can result in delayed or absent puberty and infertility. Congenital hypogonadotropic hypogonadism (CHH) and Kallmann syndrome (KS) are genetic disorders that are rooted in a GnRH deficiency but often accompanied by a variety of non-reproductive phenotypes such as the loss of the sense of smell and defects of the skeleton, eye, ear, kidney, and heart. Recent progress in DNA sequencing technology has produced a wealth of information regarding the genetic makeup of CHH and KS patients and revealed the resilient yet complex nature of the human reproductive neuroendocrine system. Further research on the molecular basis of the disease and the diverse signal pathways involved will aid in improving the diagnosis, treatment, and management of CHH and KS patients as well as in developing more precise genetic screening and counseling regime.