Invertebrate Hematopoiesis: An Astakine-Dependent Novel Hematopoietic Factor

Abstract

A novel factor, named crustacean hematopoietic factor (CHF), was identified from a library of suppression subtractive hybridization with the aim to find downstream genes of an invertebrate cytokine, astakine 1, in the freshwater crayfish Pacifastacus leniusculus. CHF is a small cysteine-rich protein (∼9 kDa) with high similarity to the N-terminal region of vertebrate CRIM1 in containing an insulin growth factor binding protein variant motif with unknown function. CHF was found to be induced in primary cell cultures of crayfish hematopoietic tissue (Hpt) cells (precursors of crayfish blood cells) after treatment with astakine 1. Silencing of CHF did not affect the renewal of Hpt cells in vitro, but induced apoptosis of Hpt cells. CHF is exclusively expressed in the blood cell lineage of crayfish (Hpt cells and blood cells), and in vivo RNA interference experiments show that knockdown of this gene results in severe loss of blood cells and a higher apoptotic rate in Hpt. Our data further suggest that crayfish CHF is critical for the survival of hemocytes and Hpt cells by preventing their apoptosis, thus it plays an important role in hemocyte homeostasis in crayfish. Our study of CHF may also shed light on the function of this untypical insulin growth factor binding protein motif located in the N-terminal of vertebrate CRIM1.

Crustacean hematopoiesis

“…In 2002, van der Braak et al conducted a thorough study that showed evidence consistent with the proposed model suggesting at least two different hemocyte lineages (Lin and Söderhäll, 2011). There is no doubt that there are several developmental stages of cells in the HPT but also that differentiation occasionally continues in circulation (Ghiretti-Magaldi et al, 1977;Roulston and Smith, 2011).…”

“…To date, the target proteinase for the SGC-specific KPI is not known. Another protein specific for the SGC lineage is crustacean hematopoietic factor (CHF) (Lin et al, 2011). Only a few proteins specific for different hemocyte types have been identified.…”

“…We have previously shown that the cell morphology within the lobules is similar in different areas of the posterior HPT, whereas some areas have more proliferating cells, and other areas have cells which are more mature and primed for subsequent released into the hemal lacunae (Noonin et al, 2012a). Noonin et al (2012) showed that the expression of an SGC marker was abundant in certain areas where proliferation was lower, and it is clear that cells with morphologies similar to type III cells, according to Chaga et al (1995), express this transcript, whereas mature GCs do not (Lin et al, 2011;Noonin et al, 2012a). It is likely that at least two separate lineages within the HPT give rise to SGCs and GCs.…”

“…This protein, CHF (crustacean hematopoietic factor), has been characterized, cloned and sequenced (Lin et al, 2011), and shown to be specific for the SGC lineage. When CHF was silenced, an increased number of apoptotic cells was detected, indicating an important role for the survival of the SGC precursors (Lin et al, 2011;Noonin et al, 2012a). However, more functional studies are needed to fully understand the function of this protein.…”

“…Interestingly, CHF is not detected in any of the insect genomes, whereas this protein is highly required for the survival of the SGC lineage in P. leniusculus and most likely other decapods (Lin et al, 2011). This protein is a small 9-kDa peptide that shares sequence similarity with the N-terminal region of the vertebrate CRIM1 protein.…”