Critical role of the neural pathway from the intermediate medial mesopallium to the intermediate hyperpallium apicale in filial imprinting of domestic chicks (Gallus gallus domesticus).

Filial imprinting in precocial birds is a useful model for studying early learning and cognitive development, as it is characterized by a well-defined sensitive or critical period. We recently showed that the thyroid hormone 3,5,3'-triiodothyronine (T3) determines the onset of the sensitive period. Moreover, exogenous injection of T3 into the intermediate medial mesopallium (IMM) region (analogous to the associative cortex in mammals) enables imprinting even on post-hatch day 4 or 6 when the sensitive period has been terminated. However, the neural mechanisms downstream from T3 action in the IMM region remain elusive. Here, we analyzed the functional involvement of the intermediate hyperpallium apicale (IMHA) in T3 action. Bilateral excitotoxic ablation of the IMHA prevented imprinting in newly hatched chicks, and also suppressed the recovery of the sensitive period by systemic intra-venous or localized intra-IMM injection of T3 in day-4 chicks. In contrast to the effect in the IMM, direct injection of T3 into the IMHA did not enable imprinting in day-4 chicks. Moreover, bilateral ablation of IMHA after imprinting training impaired recall. These results suggest that the IMHA is critical for memory acquisition downstream following T3 action in the IMM and further, that it receives and retains information stored in the IMM for recall. Furthermore, both an avian adeno-associated viral construct containing an anterograde tracer (wheat-germ agglutinin) and a retrograde tracer (cholera toxin subunit B) revealed neural connections from the IMM to the IMHA. Taken together, our findings suggest that hierarchical processes from the primary area (IMM) to the secondary area (IMHA) are required for imprinting.

Activation of human monocyte cell line U937 via cell surface calreticulin.

U937 cells were found to be activated by an antibacterial peptide, KLKLLLLLKLK-NH2 (L5), to generate superoxide anion (O2-)-like peripheral neutrophils. However, the state of cell surface calreticulin, a possible receptor for L5, was suggested to differ between neutrophils and U937 cells. Unlike the former, the latter ones were activated by anti-C-domain peptide antibody of calreticulin even in the absence of L5 and generated O2- in a GTP-binding protein (G-protein)-dependent manner.

Adenosine deaminase activity of insect-derived growth factor is essential for its growth factor activity.

Insect-derived growth factor (IDGF) was originally isolated from conditioned medium of NIH-Sape-4 cells derived from flesh fly embryos. Here we demonstrated that IDGF has adenosine deaminase activity. The substrate specificity of IDGF was similar to that of the mammalian cytoplasmic adenosine deaminase. The adenosine deaminase activity of IDGF was shown to be indispensable for its growth factor activity toward NIH-Sape-4 cells. We found that there are specific binding sites for IDGF on the surface of NIH-Sape-4 cells and that it binds to these sites with a K(d) value of 2.4 x 10(-10) m. We propose that the cell surface binding sites for IDGF are specific receptors modified with an adenosine moiety. When IDGF binds to these receptors, it may deaminate the adenosine moiety, and this process may be prerequisite for the signal transduction via this receptor.

Activation of murine macrophage-like cells by granulocytin.

Granulocytin, a C-type lectin from Sarcophaga peregrina (flesh fly), stimulated glucose consumption and cytokine production by the mouse macrophage-like cell line J774.1. When J774.1 cells were pretreated with tunicamycin, their granulocytin-dependent TNF-alpha production was greatly reduced. These results suggest that the stimulus of granulocytin is transmitted to J774.1 cells via the carbohydrate chain of granulocytin receptors located on their surface.

Male-specific IDGF, a novel gene encoding a membrane-bound extracellular signaling molecule expressed exclusively in testis of Drosophila melanogaster.

We identified a novel gene of Drosophila melanogaster, Male-specific IDGF (MSI), encoding a transmembrane signaling molecule with exclusive expression in the testis. This molecule (MSI) contains a single transmembrane domain and has 35% amino acid identity with insect-derived growth factor (IDGF), a soluble growth factor for embryonic cells of the flesh fly, Sarcophaga peregrina. When MSI was exogenously expressed in Schneiders's line 2 cells, it was shown to be localized on the cell surface and exhibits growth factor activity, suggesting that MSI is a membrane-bound extracellular signaling molecule. Gene expression studies revealed that MSI mRNA was restricted to mature primary spermatocytes, whereas MSI was detected in the cells at the later developmental stages. Analysis using four meiotic arrest mutants, aly, can, mia, and sa suggested that MSI is involved in spermiogenesis, the final differentiation step of spermatogenesis. These results suggest that MSI is an extracellular signaling molecule participating in spermatogenesis and is a new member of the IDGF family.

Hydrolysis and synthesis of substrate proteins for cathepsin L in the brain basement membranes of Sarcophaga during metamorphosis.

Previously, we identified two proteins with molecular masses of 200 and 210 kDa in basement membranes of Sarcophaga imaginal discs as substrates for cathepsin L [Homma, K. and Natori, S. (1996) Eur. J. Biochem. 240, 443-447]. Here we demonstrated that the same proteins were also present in the basement membranes of larval brains. These proteins were suggested to be digested by cathepsin L secreted from the larval brains in response to 20-HE. From the behavior of these proteins during metamorphosis, we concluded that the basement membranes of larval brains are degraded at the early pupal stage and synthesized again at the late pupal stage, coinciding with the timing of brain remodeling that takes place during metamorphosis. Possibly, the transient disappearance of the basement membranes makes brain remodeling easier, and cathepsin L is suggested to play a crucial role in the degradation of the basement membranes.